LIGO M030023-00M

Project Description

Advanced LIGO: Context and Overview

Advanced LIGO

Gravitational waves offer a remarkable opportunity to see the universe from a new perspective, providing access to astrophysical insights that are available in no other way. The initial LIGO gravitational wave detectors have started observations, and are already yielding data that are being interpreted to establish new upper limits on gravitational-wave flux.

The sensitivity of the initial LIGO instruments is such that it is perfectly possible that discoveries will be made. If they succeed, there will be a strong demand from the community to improve the sensitivity allowing more astrophysical information to be recovered from the signals. If no discovery is made, there will be no lesser urgency to improve the sensitivity of the instrument to the point where there is a general consensus that gravitational waves will be detected often and with a good signal-to-noise ratio. The development of the next generation of instrument must be pursued aggressively to make the transition from the initial to the Advanced detector in a timely way – after the complete science run of the initial detector, but as quickly as possible thereafter.

The Advanced LIGO detector upgrade meets these requirements for an instrument that will establish gravitational-wave astronomy. It is more than ten times more sensitive, and over a much broader frequency band, than initial LIGO. It can see a volume of space more than a thousand times greater than initial LIGO, and extends the range of compact masses that can be observed at a fixed signal strength by a factor of four or more.

This proposal to build Advanced LIGO has grown out of the LIGO Scientific Collaboration and has broad support both nationally and internationally from that community. A closely coordinated community R&D program, exploring the instrument science and building and testing prototype subsystem elements, has brought the design to a highly refined state. The LIGO Laboratory will lead and coordinate the fabrication and construction of the instruments, with the continued strong participation of the community.

Advanced LIGO can lead the gravitational-wave field to maturity.

The LIGO Mission

From its outset, LIGO has been approved by the National Science Foundation to directly observe gravitational waves from cosmic sources, and to open the field of gravitational wave astronomy. The program and mission of the LIGO Laboratory is to:

• observe gravitational wave sources, • develop advanced detectors that approach and exploit the facility limits on interferometer performance, • operate the LIGO facilities to support the national and international scientific community, • provide data archiving for the LIGO data and contribute computational resources for the analysis of data, • develop the software infrastructure for data analysis and participate in the search and analysis, • and support scientific education and public outreach related to gravitational wave astronomy.

1 LIGO M030023-00M

LIGO is envisioned as a new capability contained in a set of facilities and not as a single experiment. The LIGO construction project has provided the facilities that support the scientific instrumentation, and the initial set of laser interferometers to be used in the first LIGO scientific observation periods.

The facilities include the buildings and vacuum systems at the two observatory sites. The two observatories are located at Hanford, Washington and Livingston, Louisiana. The performance requirements on the LIGO facilities were intended to accommodate the initial interferometers and future interferometer upgrades and replacements, and possible additional interferometers with complementary capabilities. The requirements on the LIGO facilities were intended to permit future interferometers to reach levels of sensitivity approaching the ultimate limits of ground- based interferometers, limited by reasonable practical constraints on a large facility at a specific site.

This proposal is for the second generation of instruments to be installed in the LIGO infrastructure, and is expected to bring the science of gravitational radiation from a discovery mode to a mode of astrophysical observation.

LIGO Detector Scientific Goals

The scientific program for LIGO is both to test relativistic gravitation and to open the field of gravitational wave astrophysics. More precise tests of General Relativity (and competing theories) will be made. LIGO will enable the establishment of a brand new field of astronomy, using a completely new information carrier: the gravitational field.

Initial LIGO represents an advance over all previous searches of two or three orders of magnitude in sensitivity and in bandwidth. Its reach is such that, for the first time, foreseeable signals due to neutron-star binary “inspirals” from the Virgo Cluster (15 Mpc distant) would be detectable. At this level of sensitivity, it is plausible, though not certain, that the first observations of gravitational waves will be made. If signals are not observed with initial LIGO, we will have set challenging upper limits on gravitational wave flux, far beyond the capability of any previously existing technology.

The Advanced LIGO interferometers proposed here promise an improvement over initial LIGO in the limiting sensitivity by more than a factor of 10 over the entire initial LIGO frequency band. It also increases the bandwidth of the instrument to lower frequencies (from ~40 Hz to ~10 Hz) and allows high-frequency operation due to its tunability. This translates into an enhanced physics reach that during its first several hours of operation will exceed the integrated observations of the 1 year LIGO Science Run. These improvements will enable the next generation of interferometers to study sources not accessible to initial LIGO, and to extract detailed astrophysical information. For example, the Advanced LIGO detectors will be able to see inspiraling binaries made up of two 1.4 MO• neutron stars to a distance of 300 Mpc, some 15x further than the initial LIGO, and giving an event rate some 3000x greater. Neutron star – black hole (BH) binaries will be visible to 650 Mpc; and coalescing BH+BH systems will be visible to cosmological distance, to z=0.4.

The existence of gravitational waves is a crucial prediction of the General Theory of Relativity, so far unverified by direct observation. Although the existence of gravitational radiation is not a unique property of General Relativity, that theory makes a number of unambiguous predictions about the character of gravitational radiation. These can be verified by observations with LIGO. These include probes of strong-field gravity associated with black holes, high-order post- Newotonian effects in inspiraling binaries, the spin character of the radiation field, and the wave propagation speed.

2 LIGO M030023-00M

The gravitational wave “sky” is entirely unexplored. Since many prospective gravitational wave sources have no corresponding electromagnetic signature (e.g., black hole interactions), there are good reasons to believe that the gravitational-wave sky will be substantially different from the electromagnetic one. Mapping the gravitational-wave sky will provide an understanding of the universe in a way that electromagnetic observations cannot. As a new field of astrophysics it is quite likely that gravitational wave observations will uncover new classes of sources not anticipated in our current thinking.

Detector Design Fundamentals

The effect of a propagating gravitational wave is to deform space in a quadrupolar form. The effect alternately elongates space in one direction while compressing space in an orthogonal direction and vice versa, with the frequency of the gravitational wave. A Michelson interferometer operating between freely suspended masses is ideally suited to detect these antisymmetric distortions of space induced by the gravitational waves; the strains are converted into changes in light intensity and consequently to electrical signals via photodetectors.

Limitations to the sensitivity come from two sources: extraneous forces on the test masses, and a limited ability to sense the response of the masses to the gravitational wave strain. The thermally excited motion of the test mass and the suspension is a fundamental limitation, intrinsic to the way in which the measurement is performed; this influence is managed through the selection of low-mechanical-loss materials and designs which capitalize on them. Seismic motion causes forces on the mirrors due to the direct coupling through the isolation and suspension system, a technical noise source which is minimized through design; and due to the time-varying mass distribution near the mass (the Newtonian background).

Sensing limitations arise most fundamentally due to the statistical nature of the laser light used in the interferometry, and the momentum transferred to the test masses by the photons (linking the sensing and stochastic noise limitations to sensitivity). Technical noise sources that limit the ability to sense include frequency noise and intensity fluctuations in the laser light. Scattered light, which adds random phase fluctuations to the light, can also mask gravitational signals.

In the limit, valid for LIGO, that the instrument is short compared with the gravitational wavelength, longer arms give larger signals. In contrast, most competing noise sources remain constant with length; this motivates the 4km baseline of the Observatories. More generally, the scientific capability of LIGO is defined within the limits imposed by the physical settings of the interferometers and by the facility design, by the design of the initial detectors and ultimately by future interferometers designed to progressively exploit the facility capabilities.

Although the rates for gravitational wave sources have large uncertainty, a improvement in strain sensitivity linearly improves the distance searched for detectable sources. This increases the detection rate by the cube of the sensitivity improvement.

The Observatories LIGO Facility Scientific Capability

The LIGO facility design envisaged a progression of increasingly sensitive interferometers capable of extending the physics reach of the observatories. In the design of the observatories, LIGO incorporated critical design features into its facilities in order to optimize LIGO’s ultimate performance capabilities. These features include a building foundation and infrastructure which provides a clean, quiet environment for the instruments; a 4km long “L” ultra-high vacuum beam tube system that brings scattered light and index fluctuations due to residual gas to a negligible level; and a system of large vacuum chambers and pumping subsystems capable of providing a flexible envelope for a wide range of detector designs, and delivering a vacuum quality that

3 LIGO M030023-00M complements the beam tube subsystem. Advanced LIGO requires no changes in this infrastructure to meet its scientific goals.

The LIGO Observatories

LIGO Hanford Observatory (LHO), located on the U.S. Department of Energy Hanford site in eastern Washington, comprises 5 major experimental halls for the interferometer spread over 5 miles. 1.2-m diameter ultrahigh vacuum tubing connects these halls. Three support buildings house laboratories, offices, and an amphitheater, and two additional buildings are associated with maintenance and operations. Approximately 90,000 square feet of this space is under tight environmental control to minimize contamination of sensitive equipment. The physical plant has been designed to provide a low vibration environment similar to the surrounding undeveloped shrub-steppe environment.

LHO houses two interferometers with arm lengths of 4 km and 2 km. The 4-km equipment is installed in vacuum chambers in the corner station and the two end stations on each arm. The 2- km equipment uses vacuum chambers in the corner station and the two midstations situated halfway down each arm. The two interferometers share 2 km of beam tube along each arm. The beam tube can eventually accommodate up to 5 interferometer beams and the current station buildings can accommodate up to 3 interferometers to accommodate future growth.

Figure 1 LIGO Hanford Observatory (LHO) in aerial view. The 4-km interferometer arms are shown with the 5 main buildings shown along the orthogonal arm layout.

4 LIGO M030023-00M

Figure 2 LIGO Livingston Observatory (LLO) corner region in aerial view.

The LIGO Livingston Observatory, located in pine forests between Baton Rouge and New Orleans, Louisiana, is the site of a single 4-km laser interferometer gravitational wave detector. Construction of its physical facilities, scaled to accommodate one interferometer, is complete. The beam tube dimensions are identical to those at LHO.

Initial LIGO

Status of the LIGO Construction Project

The NSF Cooperative Agreement of May 1992 initiated LIGO Construction and Construction Related Research and Development. The Project schedule and cost estimates were reviewed by the NSF during September 1994 and presented to the National Science Board in November 1994. The total funding established by the Board for Construction and Construction Related R&D were $272.1 million and $20.0 million, respectively. In addition, the NSF provided $68.7 million for Operations through September 30, 2001 covering the period of Installation and Commissioning. The LIGO construction effort is effectively complete, on cost and close to schedule.

Initial LIGO Detector Commissioning

Installation is complete for the three interferometers. The commissioning of the instruments continues, with most subsystems completely operational and in use in the first science runs. Several subsystems are coming on-line in preparation for the next science run. The instruments have shown a steady improvement in sensitivity, at all frequencies in the planned observation band, during the commissioning process. An example of progress is seen in Figure 3. All of the instruments have made very significant progress toward the requirements proposed for initial LIGO through a process of identification, tuning, and incremental changes in the detector hardware as needed. The present limits to performance are understood through a combination of

5 LIGO M030023-00M measurement and system modeling, and measures to bring the contributors to an acceptable level are underway or in preparation.

LHO 4k strain curve evolution -15 10 Dec 29, 01: E7-recombined Jun 20, 02: pre-S1 -16 10 Sep 9, 02: S1 Dec 26, 02 LIGO science requirement -17 10

-18 10 Hz) √ -19 10

Strain (1/ -20 10

-21 10

-22 10

-23 10 2 3 10 10 Frequency (Hz)

Figure 3 This figure shows the progression in the strain sensitivity as a function of frequency for the Hanford 4-km interferometer over the year from December 2001 to December 2002. The most recent noise level is a factor 20 above the final specification over a broad frequency range; many of the sources of excess noise have been identified and are being addressed.

Future improvements to reach the design sensitivity will involve some modifications to the electronics and to the mechanical infrastructure, and optimization of control systems and filters. Substitute recycling mirrors (with an optimized radius of curvature for the observed mirror optical properties) will be installed during favorable opportunities. It is anticipated that this series of improvements in performance will largely take place between the upcoming second science run, and the third science run, planned for the Fall of 2003.

The LIGO Science Runs

The observatories are now interleaving continued commissioning with science runs. The timing of the runs is designed to balance the competing demands for improvements to the performance of the machines (in sensitivity and duty cycle) with the need to observe.

The first science run, S1, took place from 23 August through 8 September 2002, and involved the three LIGO interferometers, the UK-German GEO-600 interferometer, with some overlap in observing with the Japanese TAMA detector. The LIGO instruments operated in their design configuration, and accumulated roughly 100 hours of observation in triple coincidence between the two sites during the S1 run. LIGO Scientific Collaboration (LSC, please see below) “upper limit” groups are undertaking the search for chirp signals from binary inspirals, periodic signals

6 LIGO M030023-00M from neutron stars, burst signals from e.g., supernovae and gamma ray bursts, and from a possible stochastic noise background. The data analysis pipelines utilize a variety of sophisticated filtering techniques – templates, time-frequency analysis, inter-interferometer correlations, and use of the auxiliary and environmental data channels, as examples. Data are also being correlated with relevant optical data and, in the case of supernovae, with neutrino signals. Results from the analysis of S1 data, providing new upper limits to the gravitational wave flux, are being prepared for publication.

The second science run, S2, is planned to take place from 14 February 2003 until 14 April 2003. The objective for this run is to improve the upper limits on gravitational wave flux by at least an order of magnitude compared to the S1 run. The present sensitivity of the instruments (January 2003) enables this goal. The third science run, S3, is planned for late 2003, following a significant commissioning interval, and will represent a transition to a mode where observation dominates over commissioning at the Observatories. We plan to intersperse science runs with periods dedicated to detector improvements that will be coordinated with the LSC. The overall goal is to obtain at least one year of integrated data with an RMS strain sensitivity of h ~ 10-21 (integrated noise level in a 1 kHz band) within the first three years of observation (ending in 2006). Once that goal is achieved and the physics results have been obtained, installation of improved interferometers can commence.

LIGO Scientific Collaboration

A fundamental goal of LIGO has been to become a true national facility available to the scientific community. In order to accomplish this, LIGO has broadened the participation to include the community of scientists interested in participating in the LIGO research program by creating the LIGO Scientific Collaboration (LSC)1. There are now some 470 members, from 38 institutions in both the US and internationally. The LSC consists of both LIGO Laboratory scientists and those from collaborating groups. The LSC is organized so as to provide “equal scientific opportunity” to all members whether they are from within LIGO Laboratory or the broader LSC. It is growing steadily and will remain open to new members over the coming years. It is worth noting that the LSC has significant international participation, including collaborating groups from India, Russia, Germany, U.K, Japan and Australia. The international partners are involved in all aspects of the LIGO research program.

The full LSC collaboration meets twice yearly in an extended meeting, and various working groups meet more frequently. The LSC has produced White Papers that outline the plans for technical development of LIGO and for science data analysis. A publication policy and a conference committee are active, as well as the other functions necessary to make it a ‘full service’ organization.

The Advanced LIGO design, both in basic conception and in the detailed R&D, is very much a product of the LSC (with a strong LIGO Laboratory element). The technical working groups have been and continue to be central to the advancement of the design, and this proposal is made with the strong support of the many participating institutions in the LSC.

In addition, LIGO has been organized such that the search for astrophysical signals and interpretations will be performed through the LSC. The collaboration members committed to "LIGO I", the initial LIGO detector science runs, will be responsible for the science in this beginning phase of observation. This group in LIGO is well defined and presently consists of 111 LIGO Laboratory scientists and 134 scientists from collaborating institutions.

Preparation tasks for the runs are organized within the LSC, LSC members participate in the data taking runs, and the analysis of the data is coordinated through the LSC proposal driven process.

1 http://www.ligo.org

7 LIGO M030023-00M

LIGO is available to all interested researchers through participation in the LSC, an open organization. To join, a research group defines a research program with the LIGO Laboratory through the creation of a Memorandum of Understanding (MOU) and relevant attachments2. The group then presents its program to the LSC. When the group is accepted into the LSC it becomes a full scientific partner in LIGO.

Exploiting the LIGO Capability: Advanced LIGO

As noted above, LIGO is designed to evolve and to support improvements in gravitational wave detectors. A natural time for an upgrade to the instruments can be foreseen once the initial LIGO goal of one year of integrated observation has been met. The initial LIGO infrastructure is well designed to deliver its planned performance, and small advances in sensitivity at higher frequencies may be possible with e.g., modest increases in the input laser power. However, a large improvement will require an upgrade of the entire detector in a coordinated fashion. The considerable research and development in the Laboratory and the greater community since the initial LIGO interferometer design was frozen enables this improvement. The Advanced LIGO instrument fulfills our requirements of a significant step forward in sensitivity, and can be delivered on a time scale that meshes with the end of the Initial LIGO observation plan.

Overview of Advanced LIGO

The sensitivity goals for the Advanced LIGO detector systems are chosen to enable the advance from plausible detection to likely detection and rich observational studies of sources. These sensitivity goals require an instrument limited only by fundamental noise sources over a very wide frequency range. To achieve this sensitivity, almost every aspect of the interferometer must be revised from the initial LIGO design. The system described below is the reference concept that is the basis for structuring the R&D program and the detailed studies of system tradeoffs performed as R&D results define the feasible parameters.

The basic optical configuration is a power-recycled and signal-recycled Michelson interferometer with Fabry-Perot “transducers” in the arms. Using the initial LIGO design as a point of departure, this requires the addition of a signal-recycling mirror at the output “dark” port, and changes in the RF modulation and control systems. This additional mirror allows the gravitational wave induced sidebands to be stored or extracted (depending upon the state of “resonance” of the signal recycling cavity), and leads to a tailoring of the interferometer response according to the character of a source (or specific frequency in the case of a fixed-frequency source). The planned upgrade includes the three LIGO interferometers, allowing e.g., one interferometer at Hanford and the interferometer at Livingston to be tuned to be broadband, and the second interferometer at Hanford to be used as a higher-frequency narrowband detector.

To improve the quantum-limited sensitivity, the laser power is increased from the initial LIGO value of 10 W to ~200 W. The conditioning of the laser light follows initial LIGO closely, with a ring-cavity mode cleaner and reflective mode-matching telescope.

Whereas initial LIGO uses 25-cm, 11-kg, fused-silica test masses, the test mass optics for Advanced LIGO are larger in diameter (~30 cm) to reduce thermal noise contributions and more massive (~40 kg) to keep the radiation pressure noise to a level comparable to the suspension thermal noise; sapphire is the baseline material for the test masses. Compensation of the thermal lensing in the test mass optics (due to absorption in the substrate and coatings) is added to handle the much-increased power – of the order of 1 MW in the arm cavities.

2 http://www.ligo.org/mou/mou.html

8 LIGO M030023-00M

The test mass is suspended by fused silica fibers, in contrast to the steel wire sling suspensions used in initial LIGO. The resulting suspension thermal noise is anticipated to be less than the radiation pressure noise (in broad-band observation mode) and to be comparable to the Newtonian background (“gravity gradient” noise) at 10 Hz. The complete suspension has four pendulum stages, contributing to the seismic isolation and providing multiple points for actuation.

The seismic isolation system is built on the initial LIGO piers and support tubes but otherwise is a complete replacement, required to bring the seismic cutoff frequency from 40 Hz (initial LIGO) to 10 Hz. RMS motions (frequencies less than 10 Hz) are reduced by active servo techniques. The result is to render the seismic noise negligible at all observing frequencies. Through the combination of the seismic isolation and suspension systems, the required control forces on the test masses will be reduced by many orders of magnitude in comparison with initial LIGO, reducing also the probability of non-Gaussian noise in the test mass.

The overall performance of Advanced LIGO is dominated at most frequencies by the quantum noise of sensing the position of the test masses, with a contribution at mid-frequencies from the internal thermal noise of the test masses. This design, with modest enhancements after it enters scientific use, should take this interferometer architecture to its technical endpoint; it is as sensitive as one can make an interferometer based on familiar technology: a Fabry-Perot Michelson configuration with external optical readout using room temperature transmissive optics. Further advances will come from R&D that is just beginning, such as the exploration of cryogenic optics and suspensions, purely reflective optics, and a change in the readout to one which fully exploits our nascent understanding of the quantum nature of the measurement (e.g., quantum non-demolition speed meters). These later developments will be timely for instruments to be developed in the second decade of this century.

Advanced LIGO R&D 2002-2006

During 2002 through 2006, most LIGO Laboratory detector R&D is being directed at the challenges posed by the Advanced LIGO design. This R&D program is a significant part of the larger R&D program of the LIGO Scientific Collaboration. The LSC program has been developed in a collaborative manner and is coordinated through the LSC Working Groups and by the LIGO Laboratory.

The R&D program currently underway, supported by the NSF under cooperative agreement PHY- 0107417, is designed to support this construction proposal. This proposal requests that construction funding commence at a time when the major R&D issues are satisfactorily resolved, and the subsystems are ready for fabrication.

The activities carried out prior to construction funding include small-scale fundamental research motivated by Advanced LIGO. Examples of this are studies of core optic substrate absorption, measurement of mechanical losses in suspension fibers, and studies of candidate photodetectors for the gravitational wave readout. The R&D program also includes large-scale prototypes of subsystems such as full-scale seismic isolation systems, full-scale suspensions, and full-scale core optics. In order to carry out this research, in most cases these components must be fully engineered to the realistic requirements and configuration of Advanced LIGO. In order to study the performance and control of a suspension subsystem, the prototype studied must represent the Advanced LIGO design down to details such as suspension fiber material, bonding technique, and control electronics design and component selection and physical layout. This kind of rigorous full-scale development program is needed to reduce risks prior to defining and committing to a construction project.

Advanced LIGO Schedule and Cost

9 LIGO M030023-00M

The Advanced LIGO fabrication and construction schedule grows out of the tightly coordinated R&D program currently underway. The objectives in establishing the schedule are to • Allow the initial LIGO instruments to be fully exploited, and in particular to ensure the commitment to a full integrated year of observation with initial LIGO instruments. • Allow a complete R&D cycle, with extensive testing of final designs, before committing to fabrication. • Bring the Advanced LIGO instruments on-line as quickly as possible to meet the demands of the community for the observing capability of the Advanced LIGO detector.

The schedule is based on our extensive experience with the design, fabrication, construction, and commissioning of the Initial LIGO detectors.

The highlights of the schedule are • Receipt of funding for the fabrication and construction project in early 2005, with some advance funding for critical long-lead items in early 2004. • Delivery of first interferometer hardware to the observatory staging facilities in mid-2006. • Decommissioning of initial LIGO at the LIGO Livingston Observatory in early 2007, and simultaneous start of installation of Advanced LIGO there. • Decommissioning of initial LIGO at the LIGO Hanford Observatory in late 2007, and simultaneous start of installation of Advanced LIGO there. • Both observatories in commissioning by mid-2008. • Both observatories in operation by late 2009.

The cost estimate developed for this proposal was performed at the lowest feasible level, given the present level of development in the WBS, in a bottom-up manner. Most subsystems have been costed at a level of detail comparable to initial LIGO; several have not achieved the maturity in R&D to allow this level of detail, but carry contingency appropriate to the basis. The techniques used were the same methods used to estimate initial LIGO construction costs, though our cost experience in initial LIGO substantially improved the input knowledge base for the new estimate. Contingency was estimated using the formal graded approach to assessing technical, cost and schedule risk that was used in initial LIGO.

The joint United Kingdom/German GEO Project3 has proposed to provide a capital investment in this construction project. The UK proposal is for approximately $11.5 million. They propose to apply these resources to providing the suspension subsystem, including suspension assemblies, their controls, and installation and commissioning. The German proposal is for the design and fabrication of the pre-stabilized laser subsystem, and the value of the contribution is also planned to be valued at $11.5 million. The GEO Project is a full partner in Advanced LIGO, participating at all levels in the effort.

With the GEO capital contribution, the required US Advanced LIGO costs are $ XXXXX K in FY 2002 $. Escalating this sum to the approximate mid-point of Advanced LIGO construction (2006), using the average inflation rate quoted by the US Department of Labor for the last 6 years (2.4%), yields a total request to the NSF for constructing Advanced LIGO of $ XXXXX K.

3 http://www.geo600.uni-hannover.de/

10 LIGO M030023-00M

Results and Accomplishments from Prior Support

This section describes the state of the LIGO Laboratory at the close of 2002, summarizing the status of the construction, commissioning, operations, data analysis, collaborative research and support of the involved community, advanced detector R&D and efforts on education and outreach designed to produce broader impacts of LIGO. Further details are available in the references.

The narrative description of progress follows the task organization of the LIGO Laboratory in 2002.

Observatory Operations and Detector Commissioning

The Detector and Engineering Groups and the Observatory staff are focused on commissioning and operating the interferometers. Emphasis is on reducing noise and improving duty cycle and on refining the design and implementation of interferometer subsystems based on our growing operational experience.

At the close of 2002 we had achieved strain sensitivity better than has been achieved with any previous broadband detector for all three interferometers. This was the case over the entire gravitational wave band from 100Hz to several kHz. These improvements contributed to a very successful first Science Run (S1) and position us well for the S2 run in February, 2003.

Hanford and Livingston Observatories

The sensitivity of the interferometers continued to improve in 2002. This improvement resulted from control subsystems being brought into operation, improvements in the performance of electronics and software subsystems, and tuning of the controls system.

We made steady progress improving sensitivity for both interferometers, achieving best noise equivalent strain sensitivity better than 8×10-22/√Hz in the four-kilometer interferometer (H1) and 3x10-21/√Hz in the two-kilometer interferometer (H2), and 3×10-22/√Hz I at the Livingston four- kilometer interferometer.

Engineering runs 6, 7 and 8 were conducted to test the interferometers. During E7 the interferometers were operated in coincidence between the two Observatories, with GEO-6003, and with ALLEGRO4, the cryogenic resonant bar detector at Louisiana State University (LSU).

All interferometers participated in the first Science Run (S1) from August 23 to September 9, 2002, collecting nearly 100 hours of triple-coincidence data. GEO-600 and TAMA5 also scheduled observing runs to coincide with S1.

At both Hanford and Livingston we completed the last phase of facilities construction, providing laboratory, office and meeting space. We hired additional staff required as we approach twenty- four-hour-per-day, seven-day-a-week operation.

4 http://gravity.phys.lsu.edu 5 http://tamago.mtk.nao.ac.jp/

11 LIGO M030023-00M

LLO 4k strain curve evolution

-15 May 18 01 10 Dec 20 01

-16 Jun 13 02 10 Jan 6 03

-17 LIGO science requirement 10

Hz) -18

√ 10

-19 10 Strain (1/

-20 10

-21 10

-22 10

2 3 10 10 Frequency (Hz) Figure 4 Strain sensitivity improvement for the Livingston 4-Km interferometer during 2002.

Engineering Runs

The seventh engineering run started on December 28, 2001, and data collection was completed January 15, 2002. The Livingston four-kilometer interferometer and the Hanford two-kilometer interferometer had a combined duty was about 40 percent. The overlap was primarily at night when the seismic conditions at Livingston were relatively quiet (this operational limitation is being addressed; see elsewhere). Combined observations with the bar detector at Louisiana State University (LSU) began on Wednesday, January 9. Concurrently, GEO operated a power- recycled Michelson interferometer.

We conducted an engineering run (E8) from June 8 to June 10, 2002 at the LIGO Hanford Observatory. The objective was to evaluate the Data Monitoring Tool (DMT) software developed by the LIGO Scientific Collaboration (LSC) in preparation for the first science run (S1). We tested sixteen monitoring programs under real operating conditions. Useful recommendations for needed modifications were provided to software authors. As a result, DMT programs ran reliably and usefully during S1.

DMT is an elaborate and useful suite of programs that continuously review the interferometer data streams, watch for various potential problems, and record summary information for later use concerning the three interferometers and their environments. DMT also supports interactive exploration of the data in the gravitational-wave channel and of non-linear noise processes. It supplies the non-strain-channel 'vetoes' used to improve the statistics of the processed strain data.

12 LIGO M030023-00M

Science Runs

We have planned an initial progression of three science runs, interleaving interferometer development and improvement with increased scientific reach for each run. Important data analysis, and interferometer commissioning and development work are implemented between the scientific running periods. The three consecutive runs will provide a baseline for LIGO Data Analysis System (LDAS) development, detector modeling and diagnosis, as well as interferometer commissioning, modification, and revision. All three science runs are the joint responsibility of the Laboratory and the LSC.

We completed a very successful first science run (S1), ending on September 9, 2002. Analysis of the data from this run, and further interferometer commissioning and modification is under way. S1 was a showcase for a variety of new and improved DMT monitors. The LSC conducted an important November 2002 teleconference to summarize the status of the data analysis effort and define the path towards reporting results. Release of results for publication from the S1 analysis is planned for February 2003.

The experience gained during S1, including complete upper-limit operation and orientation of the LIGO-LSC scientific and operations staff, will help us to prepare for the second science run (S2), scheduled start in February 2003.

The S1 run included coincidence operation with the GEO3 600 interferometer and TAMA5 300 detector. This coincidence effort promises additional results and early experience running a network of detectors across the globe.

Further commissioning prior to S2 is nearing completion and is a staged “freeze” to the configuration of the three interferometers will take place in late January 2003. The goal for S2 is at least an order of magnitude improvement in scientific reach, and we plan S2 to last approximately 8 weeks. With the presently realized improvements in strain sensitivity and duration, S2 will provide an opportunity to set very significant upper limits. We expect that S1 and S2 data will provide new publishable limits on the broadband gravitational wave flux, well beyond what has been previously reported.

Following S2 we plan additional commissioning including the important installation of the Livingston seismic pre-isolation system. S3, scheduled for late 2003, will mark the beginning of the first true search for gravitational waves with astrophysical significance.

Commissioning

At the close of the year we had achieved similar performance levels with all three instruments (H1 and H2 at Hanford, L1 at Livingston). We accomplished this by upgrading all hardware to the same revision and sharing commissioning experience through close collaboration and personnel exchanges between observatories.

The most significant changes were the installation of and completion of the commissioning of the digital suspension controllers. This second version of the electronics for pointing and actuating the test masses provides great flexibility in the design of (digital) filters to allow large actuation forces outside of the gravity-wave band to counter seismic motion, but very low noise operation in the target band. In addition, mechanical cross coupling in the suspensions can be 'inverted' to decouple length and angle motions.

In a related effort, the optical levers were refined and tuned. The optical levers provide an independent measure of optical alignment and are used to establish the initial alignment of the

13 LIGO M030023-00M instruments in preparation for locking (brought into the linear control regime) . They can also be used to maintain the alignment during operation for those degrees of freedom, in anticipation of the completion of the wavefront sensor commissioning. The digital filtering capabilities of the suspension controllers improved the low-frequency performance of the optical levers and thus the overall interferometer sensitivity.

In the length control system, experience indicated that a change in control topology could provide a significant reduction in the appearance of frequency noise in the strain output. Once the instrument is locked an automated script transfers actuation away from the test masses and to the mode cleaner and laser systems. This also provided improvements in the low-frequency regime.

The improvements in the controls allow us to increase the light intensity on the main sensing photodiodes, reducing the photon shot noise at high frequencies. We moved from being dominated by electronics noise to seeing the quantum noise, as anticipated by the interferometer design.

At the Livingston Observatory, seismic noise in the 1-3Hz band arising from tree harvesting, traffic, and other human activity in the area surrounding the site continues to limit the operation of the interferometer to periods of low seismic noise, generally night time and weekends. Weather noise in the 0.1-0.3 Hz band has also interfered with operation at times. In response to these disturbances, several technical approaches have been initiated. We worked together with our LSC collaborators at Louisiana State University (LSU), to incorporate the fine actuators at the end masses into a feedback loop to reduce the seismic motion of the stacks between 1 and 10 Hz. These actuators remove the differential motion due to the tides and reduce the microseism. Using four longitudinal actuators at the corners of the support beams and two geophones as inertial sensors mounted on the beams, we reduced the Q's of the stack mode at 1.2 and 2.1 Hz by a factor of seven. These are the key modes for the excess test mass excursions driven by seismic motion at Livingston. This near-term solution to reduce excess seismic noise due to logging in the vicinity of the interferometer will be supplanted by the pre-isolator after S2 (see section Seismic Isolation Upgrade below.) In the interim, we can achieve higher duty cycle and greater sensitivity.

Investigations of Radio-Frequency Interference (RFI) and Electromagnetic Interference (EMI) in the detectors indicate that we have been suffering contamination from the switching-mode power supplies used as well as cross-coupling from digital electronics to low-level analog electronics. By modifying some power supplies (to linear models) and changing cabling and cabling configuration we successfully reduced the RFI/EMI in the subsystems selected. We have developed a comprehensive plan to address the contamination, which will be executed in stages starting after the end of S2.

Seismic Isolation Upgrade

We are developing a pre-isolator to address the excess seismic noise at Livingston. The technical solution is an early implementation of the external pre-isolator for Advanced LIGO. Our LSC Stanford University collaborators transferred their basic conceptual design for the hydraulic portion of the system to the LIGO-LSC collaboration for continued development. Prototypes for both the Hydraulic External Pre-Isolation (HEPI) and Electro-Magnetic External Pre-Isolator (MEPI) prototypes are complete and testing and control law development is underway. We plan to complete the testing and to fabricate and install the pre-isolator at Livingston shortly after the S2.

We installed and tested Piezoelectric External Pre-Isolation (PEPI) in the End Test Mass (ETM) and Input Test Mass (ITM) chambers at Livingston as an interim approach to reducing the influence of seismic noise. We also finalized the design for coarse actuation/adjustment for the

14 LIGO M030023-00M

ITM chambers. This reduces the differential- and common-mode test mass actuator dynamic range requirements by a factor of 3, and allows a higher duty cycle for the instrument.

15 LIGO M030023-00M

Data and Computing Group

Simulation and Modeling

We improved the second generation LIGO simulation package based on the end-to-end (e2e) time domain simulation engine to incorporate more realistic hardware and servo system models with the latest detector designs. Notably important recent additions include the Wave Front Sensor (WFS) and the Alignment Control System using WFS signals, and the common mode servo. Our ability to simulate LIGO end-to-end is nearly complete.

Sample sensitivity curves simulated by the model and the LIGO sensitivity measured during S1 are shown in Figure 5.

Figure 5 Actual and simulated sensitivity noise for S1.

While additional adjustment of the input parameters of the simulation in Figure 5 is needed, the good agreement demonstrates the relative completeness of this model. Note that the simulated noise curve is calculated from simulated time-series data (ground noise, input photon shot noise, electronics noise, etc.), enabling simulation ‘experiments’ of changes in the isolation system, control law tuning, etc., without disturbing the actual interferometer.

We have improved the time domain simulation code to support the more demanding functionalities of the simulation code. Recent improvements include a more accurate treatment of the response of the Core Optics Component to the frequency noise and improvements of the

16 LIGO M030023-00M

Modal Model. Other improvements include an interface, which makes it possible to run the simulation under different conditions, analogous to changing the hardware or software setup during LIGO operation, without human intervention. These changes make it even easier for non- expert to use and extract more useful information.

A new object-oriented field/optics model is being developed. The new scheme makes it possible to easily implement realistic features like wedge angles or internal reflections in substrates.

Commissioning Modeling

Interferometer locking at the Livingston site is being compromised due to seismic noise induced by passing trains and on-going logging activity near by. The effects of these seismic noise sources on the interferometer performance are being modeled to support the required design modifications in the seismic isolation system.

Now that the wave front sensing is fully implemented in the simulation, we have begun a collaboration to understand the complex response of the real LIGO wave front sensing. We have modified the simulation program interface to make it easier for the non-expert to use it and analyze the response.

We investigated the effect of heating of the input test mass (ITM) after a long time in lock at a high input power using the Han2k package (the first generation LIGO simulation model used for the lock acquisition design). The study showed that the model could cover a satisfactorily wide range of ITM deformation.

Alfi5—Graphical Front-end

Alfi5, a new version of alfi completely rewritten using Java, was stable from the first day of its release. Refinements have improved stability and reliability. All features in the previous versions written in C++ are now fully implemented in the new version. We added many new features to make this “e2e editor” much more useful and convenient. Examples include copy and paste capability, and the easy arrangement of port locations. When alfi was written in C++, it was distributed together with the simulation code. Now the Java version is distributed as a separate compact package. This makes it easy to distribute new versions in a timely manner.

Near Term Plans

Now that the simulation package is almost completed, the focus will move to the application simulation to assist in the noise reduction effort for all three interferometers. We are working towards establishing an effective simulation effort at each LIGO site. Three major development areas are planned: support of mirror imperfections, implementation of a refined field/optics model in the e2e simulation engine framework, and speed improvements of the simulation code. Alfi5 development will continue. Although basic features have already been incorporated, further refinements are needed to improve productivity.

LIGO Data Analysis System (LDAS)

LDAS Software Development

LDAS software development continued through 2002. Preparations for engineering run E7, and for the first science run (S1) drove our effort. We applied lessons learned during E7 to our current LDAS release (0.5.0), which was used during S1. Intense use of LDAS during E7 and S1 enhanced our understanding of the user and usage modes. LDAS systems are now being used at all Laboratory sites as well as at several LIGO Scientific Collaboration (LSC) Institutions

17 LIGO M030023-00M

(University of Wisconsin at Milwaukee, Penn State University, University of Texas at Brownsville, and Australian National University). LDAS 0.5.0 uses the new international standard (FRAME 6) for frame data storage.

We used LDAS version 0.5.0 during S1, and subsequently for all upper limits analyses. We achieved significant improvements in the system performance, grid safety, and memory management. LDAS 0.5.0 is the first release to have a diskCacheAPI that can manage raw data on the large RAID6 storage systems now on-line at Hanford and Livingston This release performed reliably, to the 99 percent level, on S1, up from the approximately 90 percent level for the release used during E7. LDAS 0.5.0 also produces reduced frame data files, which are easier to share. Experience with the more than 10 terabytes of data collected during E7 has underscored the fact that we will need this capability for longer data runs.

We added a new frame CPP library to LDAS. We made significant improvements in the processing efficiency and enhanced the interface protocol used by the search codes to support raw sequences in data exchanges. Thorough testing and the sharing of pre-release frame files with the Virgo7 project (Italian-French laser interferometer collaboration) have allowed us to significantly improve the reliability of the code, and assure compliance with the specification.

The LIGO Scientific Collaboration (LSC) upper limits groups used LDAS online during the science run S1, and nearly 230,000 jobs were submitted to the Hanford, Livingston, and MIT systems during the run. This is roughly twice the number of jobs submitted during E7. These jobs inserted over 7,000,000 rows into the databases. This represents roughly the same number of triggers and events as were produced during E7 even though the burst group chose not to enter their event candidates into the database during this run.

LIGO data collected during E7 and S1 was successfully transferred from the remote observatories to the Caltech archive and from there, using secure mechanisms based on GriPhyN8 (see “Grid Computing and Related Research” below) tools, to the LSC Tier 2 Computational centers where members of the LSC are conducting a significant proportion of the LIGO science.

LDAS Hardware

The primary activity was upgrading the Storage Area Network (SAN) and the compute clusters at the Hanford and Livingston Observatories in preparation for the first science run (S1). The production analysis system at Caltech is fully operational with all of the servers integrated with Beowulf clusters. In addition to an initial 16-node Beowulf cluster, we installed a 17-terabyte-disk farm holding all of the S1 data. All of the LDAS servers in five of the six LIGO Laboratory run LDAS systems have been upgraded to Gigabit Ethernet networks. The Gigabit Ethernet network was also replicated at the Observatories where it connects the main buildings housing data acquisition equipment to the new facilities housing the LDAS equipment.

SunFire880 servers were integrated into the existing LDAS systems to operate as the main data servers. The large disk storage systems at the observatories were moved to the new servers. All engineering and science run data generated by the LIGO Laboratory have been archived at Caltech in the LIGO data archive running HPSS9. The current archive10 contains 54 terabytes.

6 RAID - Redundant Array of Independent Disks 7 http://www.virgo.infn.it/ 8 8 GriPhyN: Grid Physics Network, the GriPhyN Project is developing Grid technologies for scientific and engineering projects that must collect and analyze distributed, petabyte-scale datasets. GriPhyN research will enable the development of Petascale Virtual Data Grids (PVDGs) using a Virtual Data Toolkit (VDT). (http://www.griphyn.org/index.php) 9 The High Performance Storage SystemTM--IBM (HPSS); http://www4.clearlake.ibm.com/hpss/index.jsp 10 http://www.ldas-sw.ligo.caltech.edu/archive/hpss

18 LIGO M030023-00M

After a thorough review and with consultation from experts in the field, we decided to replace HPSS platform with SAM-QFS11. The SAM-QFS archiving platform offers a number of important enhancements relative to HPSS namely: simplicity, reliability, ability to move media between systems without data replication, sufficiently low licensing fees to allow use at the Observatories as well as Caltech, disaster recovery, metadata performance, and minimization of the number of vendors supporting LDAS. Initial testing and disaster recovery experiments have gone well. A demonstration run during S1 verified SAM-QFS performance as well as its capability to archive and retrieve the 17 terabytes of S1 data without corruption. We are in the process of negotiations with Sun for the licensing fees.

We are adding a grid interface currently installed at Caltech to the LIGO LDAS systems at Hanford and Livingston Observatories, and at MIT. We are expanding the existing LIGO compute clusters at Caltech, Hanford, Livingston, and MIT with additional nodes to establish sufficient processing capability for scientific analysis. A procurement of up to1000 central processing units is anticipated during the first half of the next fiscal year. A trade study is currently under way to choose between the currently used Intel hardware and newer technology that offers significant cost or performance advantages.

We are also planning to expand our data storage capability at all LIGO sites. We have been evaluating the feasibility of using Large Disc Storage IDE technology for non-critical path components. The IDE tape storage alternative is a factor of 10 less expensive than the comparable SCSI product. IDE disc technology, though less expensive, might even surpass SCSI disc storage capability. We have purchased 10 terabytes of IDE disc storage to support a technology demonstration.

Grid Computing and Related Research

LIGO is making strides towards performing scientifically significant data analysis using Grid resources. As part of the collaboration between the LIGO and the GriPhyNError! Bookmark not defined. projects, this past year we have focused on a specific LIGO problem: the gravitational-wave periodic source (“GW pulsar”) search. The data needed to conduct the search spans a significant period of time (~4 months, 2×1011 points). A source would appear on the frequency-time image as a wavering line, whose frequency might be 1 kHz, but modulated by a few parts in 106 over a day and a few parts in 104 over a year. In addition, if the source exhibits any secular variations due to slowing down of its rotational period, these will be encoded in the data as well. We successfully ran more than 50 pulsar searches, collecting useful statistics on the performance of the system for future improvements12

We have successfully integrated LIGO's existing data analysis with a Grid environment interface. The LIGO Data Analysis System (LDAS) can perform a wide range of sophisticated and computationally intensive data analysis. We are developing an infrastructure in which LDAS can be accessed as a Grid resource and to also enable LDAS to schedule its jobs on the Grid.

General Computing

We have completed and implemented the General Computing Policy. An accompanying computing and IT security plan was also developed and adopted. A baseline security audit was conducted at all four LIGO sites. A number of issues were discovered and addressed. We are developing a schedule for additional audits during FY 2003. Security and related services have a high priority. Additional network security hardware will be installed at all locations.

11 SUN Storage and Archive Management system 12 The statistics are summarized at http://smarty.isi.edu:8680/cgi-bin/final.pl

19 LIGO M030023-00M

We converted the Hanford Observatory network connection to the DOE ESnet through PNNL13 from a T1 line to 10 Megabit ethernet-over-fiber. This required purchasing and installing media converters at both ends of the connection, PNNL and Hanford. We are preparing to move from the ethernet network to an OC3 network connection through ESnet. This upgrade is scheduled to take place during the first half of FY 2003.

A new web server was added that is devoted exclusively to LIGO Scientific Collaboration (LSC) web sites. We acquired the domain name, ligo.org, for this server through a charitable gift.

Campus Research Facilities

40-Meter Laboratory

LIGO operates a 40-Meter prototype gravitational-wave interferometer on the Caltech campus. To prototype the Advanced LIGO optical configuration and controls, and study its performance, a fully instrumented suspended-mass interferometer is needed. The 40-Meter facility is dedicated to this task.

A Conceptual Design Review for the 40-Meter Dual Recycling project was held in October 2001. At that time, detailed conceptual designs were presented (with accompanying documentation) for the overall project, the tentative optical configuration and control scheme, the optical layout, all sensing table instrumentation, core suspended optics, mechanical suspensions, digital suspension controllers, and auxiliary optics (stray light control, initial alignment system, optical levers, video monitoring, etc), laboratory infrastructure and vacuum systems, environmental monitoring, data acquisition, computing and networking. Progress on key components was reviewed. The schedule of milestones was presented and discussed. The review committee was satisfied with the design and the progress, and a few specific concerns were addressed.

As of January 2003, we are on schedule. In particular, the following components and subsystems are implemented:

• The infrastructure has been brought to specifications. The laboratory building has been expanded and upgraded, all electronics racks needed for the full interferometer controls have been installed, and all optical tables and optical enclosures have been installed. Vacuum equipment (pumps, gauges, RGAs) have been upgraded. • The existing vacuum envelope has been augmented with a new output optic chamber with seismic stack, a 13-meter mode cleaner beam tube, a small chamber and seismic stack for the end mode cleaner suspended optic. • A commercial active seismic pre-isolation system (STACIS) was installed on all four test mass chambers and is now in continuous use. • An Initial-LIGO pre-stabilized laser (PSL) was installed in spring 2001. It has been fully commissioned and characterized, and is in continual use. • The optics and suspensions for the 13-meter mode cleaner were produced, and in April 2002, the three suspended optics for the mode cleaner were hung, tested, and installed into the vacuum envelope. • The characterization of the mode cleaner performance, and its interaction with the pre- stabilized laser system, occupied much of fall 2002. By the end of December 2002, the noise performance of the system met specifications. • All of the core optics and suspensions for the main dual recycled interferometer (including spares) were produced August 2002. Three core optics (the beamsplitter, ITMx, and ITMy) were suspended and damped in September 2002.

13 Pacific Northwest National Laboratory

20 LIGO M030023-00M

Thus, there has been considerable progress in the fabrication and commissioning of a full dual- recycled interferometer with LIGO-engineered controls. To complete the fabrication phase, the remaining optics and suspensions must be installed, and some additional sensing and control electronics must be designed and fabricated. These systems will be installed, and the process of commissioning them begun, by summer 2003. First experiments in dual recycled configuration response, lock acquisition, and control are planned for 3Q 2003, and are expected to take at least a year. We expect that LSC members, as well as students, will participate in this most interesting phase of the project.

MIT Facilities (LASTI)

The LIGO Advanced System Test Interferometer (LASTI) facility is designed to develop and test advanced and improved LIGO subsystems at full mechanical scale, without disrupting or delaying scientific operations at the observatory sites. Located in a purpose-built high bay laboratory on MIT's northwest campus, LASTI comprises a suite of vacuum chambers and beam tubes (on a much-reduced 16m baseline), seismic isolation supports, lasers, and electronic and computing infrastructure closely replicating those found at the Livingston and Hanford LIGO observatories.

Figure 6 The LASTI vacuum envelope. The system consists of three ‘HAM’ auxiliary optics chambers, one ‘BSC’ test mass chamber, connecting tube, and pumping system. The photo is looking along one arm; taken before the seismic isolation support piers and clean rooms were installed.

During fiscal 2002, LASTI was primarily dedicated to accelerated development of seismic pre- isolators for the Livingston Observatory, which has been impacted by excess environmental noise

21 LIGO M030023-00M due to nearby human activity. Prior to discovery of this phenomenon, LASTI had been slated to receive prototypes of the fully active seismic isolation systems planned for advanced LIGO. To accommodate testing the initial LIGO pre-isolator retrofit, we instead rapidly installed an initial LIGO isolation stack into our BSC (Basic Symmetric Chamber) early in the year. Another chamber, one of our three HAM (Horizontal Axis Modules), already carried an initial LIGO isolation stack used in prior work commissioning our laser stabilization system (see below).

We systematically characterized these initial LIGO stacks to establish similarity with the Livingston instantiations and to explore off-diagonal modes not previously measured. These measurements allowed development and confirmation of a dynamic numerical model that predicts the reactances and transmissibilities of these fairly complex "payloads" for external forces14

Two variants of an external isolator were prepared for testing, differing principally in their force actuator technology. The HEPI (Hydraulic External Pre-Isolator) system is based on laminar-flow hydraulic differential pistons, originally developed by Stanford University15. Eight prototype actuators and a regulated hydraulic supply system were engineered by a collaboration of engineers and scientists from Stanford, LIGO Livingston, Caltech and MIT and installed near the end of 2002 on the LASTI BSC chamber. This system is currently undergoing actuation trials.

A second external actuator variant, dubbed MEPI (Magnetic External Pre-Isolator), was simultaneously developed at MIT. This alternative may potentially afford lower complexity and cost than the hydraulic system, at the expense of somewhat lower stroke and force capability. A suite of eight MEPI force actuators was fitted to one of the LASTI HAM chambers in the third quarter of 2002 and is undergoing closed-loop control tests. The two-actuator variants share a common physical mounting, designed for direct compatibility with existing LIGO structural interfaces. Selection of one of the variants is expected in the first quarter of 2003, to be followed by intensive development to refine, test and replicate the design for installation at the LIGO Livingston observatory.

During 2002 the LASTI prestabilized laser also served as the development platform for an improved Pre-Stabilized Laser (PSL) frequency/phase control system. The fielded laser stabilization electronics operate reliably, but have routinely failed to achieve unity-gain bandwidths in excess of 200 kHz. This has limited the performance of successive phase and frequency loops, which depend hierarchically on this initial stabilizer to determine their own bandwidths. Using the LASTI PSL as a trial platform, modified electronics were developed and tested; a bandwidth exceeding 1 MHz was achieved along with significant improvements in robustness and reliability. These developments are now being engineered into an upgrade for the observatory laser systems, slated for installation in the second quarter of 200316

Finally, during 2002 LASTI scientists wrapped up characterization of a full quadruple-pendulum Advanced LIGO suspension mockup. This prototype, with metallic dummy masses and wires in place of the eventual sapphire and silica mirrors and fibers, was assembled by collaborating scientists from University of Glasgow, Caltech and MIT in the LASTI high bay and tested to validate dynamical and control models. Several iterations to both the mechanical system and its simulation brought them into sufficient agreement to develop a refined design for the advanced mirror suspensions. This design is now in fabrication at Caltech, and a first article is scheduled for delivery to LASTI in the first quarter of 2003.

14 “Vibrational Modes of the BSC Seismic Isolation System,” T020046; “Vibrational Modes of the HAM Seismic Isolation System;” Hytec Inc., 1998, T020045 15 S. Peirce, H. Tran, M. Wiedemann, and D. DeBra, “Quiet Hydraulics for Ultraprecision” Actuation,” in Proceedings of ASPE Spring Topical Meeting on Mechanisms and Controls for Ultraprecision Motion, Tucson Az., 1994. 16 McKenzie, Rollins, Ottaway & Zucker, T020097-00-D, LIGO-T030012-00-D (in preparation)

22 LIGO M030023-00M

Research and Development toward Advanced LIGO

This year we initiated or continued a broad range of research and development to support the Advanced LIGO concept. This effort is very strongly collaborative, and the highlights of the progress in 2002 described below are often the result of collaborations with other institutions in the LIGO Scientific Collaboration (LSC).

Seismic Isolation

The seismic isolation team focused on the pre-isolator development for initial LIGO described above. This advance implementation of the pre-isolator is, in addition to an important near-term aid for the Livingston interferometer, also a significant step forward for the Adv LIGO seismic isolation system. A photograph of the hydraulic-actuator variant is shown in Figure 7.

Figure 7 Hydraulic pre-isolator (HEPI) vertical isolator. On the left, the vertical actuator is shown; differential pressure in the bellows exerts force on the septum in the middle, which is carried to the load via the pyramidal flex joint at the top. On the right, the actuator is shown as installed at the MIT LASTI testbed.

A second-generation active isolation system prototype was designed by the LSC team and fabricated by the LIGO Laboratory. It is currently being commissioned at the Stanford Engineering Test facility. A photograph of the prototype is shown in Figure 8. This technology demonstrator will be used to (a) inform the development of the full-scale LASTI seismic systems for the HAM and BSC chambers, which will be developed this coming fiscal year and (b) serve as a controls test bed for the active isolation systems. Initial testing of the demonstrator show that a key measure of intrinsic mechanical alignment, the coupling from a requested horizontal actuation to an accidental tilt of the platform, is very low, which will ease the low-frequency controls design. Other measurements indicate that the first internal mechanical resonance, which will limit the maximum control loop bandwidth, is roughly 200 Hz, compatible with the design goal of 50 Hz for the loop bandwidth.

23 LIGO M030023-00M

Figure 8 Photograph of the prototype at the Engineering Test Facility (ETF), at Stanford, of the in-vacuum seismic isolation system. The trapezoidal springs which support the outer and inner stages can be seen; the cavity at the lower left is one of six (3 outer, 3 inner) cavities which receive a plug-in unit containing sensors and actuators

Testing and control law development will continue on this system during 2003. A request for bid for the next generation prototype is in preparation and will be issued in early 2003, enabling the delivery to LASTI in late 2003.

Suspensions

An all-metal test mass quadruple suspension prototype was developed at the University of Glasgow GEO lab and then sent to MIT for testing. All of the solid body modes were identified, and the model for the suspensions developed at Caltech, Stanford, and Glasgow was refined. Further trade studies on the lengths and masses were made based on the updated model. A challenge in the design is to damp the solid-body modes of the suspension without introducing excess noise in the gravitational-wave band (10 Hz and higher). Several approaches are being followed: using passive eddy-current damping, development of a miniaturized interferometric sensor, and an approach using a split feedback system has been developed in VIRGO17

An analysis of the thermal noise of tapered fused silica fibers at Caltech showed that this is an attractive alternative to ribbons for ease of fabrication and ultimate thermal noise performance. Some first samples have been fabricated for tests. Development of ribbons continued at Glasgow as the baseline design. Refinement of the attachment technique of the fused silica suspension fibers to the masses, using hydroxy-catalysis bonding, to sapphire (for the test mass) and high- density glasses (candidate for the penultimate mass) was made with good success.

17 VIRGO, French-Italian gravitational-wave detector and consortium, http://www.virgo.infn.it/

24 LIGO M030023-00M

We have completed the design and fabrication of the first prototype auxiliary optics suspensions; see Figure 9. This suspension design carries the mode-cleaner optics, and will first be exercised at Caltech to check the solid body modes and damping characteristics, and then transferred to the MIT LASTI facility to look at installation and control issues.

Figure 9 Photograph of the prototype of a triple suspension design for the Mode Cleaner mirrors. The dummy optics is made of aluminum with holes bored to match mass and inertia for the final silica optics. The prototype has coil actuators on all three levels, identifiable as white ceramic cylinders.

A significant step in 2002 was the installation of the complete set of triple-pendulum fused-silica fiber suspensions in the GEO-600 interferometer by the GEO project. The Advanced LIGO suspension design is directly derived from the GEO-600 design, and the test of fabrication, installation, and now ultimately performance of the working design will be invaluable for refining the Advanced LIGO design.

Optics

25 LIGO M030023-00M

We made significant progress in producing and characterizing sapphire as the preferred test mass material for Advanced LIGO. Our industrial partner fabricated full-sized boules (see Figure 10) that will now be polished to allow a more complete characterization.

Figure 10 Sapphire substrate pathfinder. This piece, fabricated by Crystal Systems, Inc., is the full size of an Advanced LIGO test mass, 32 cm dia, 40kg mass. (Courtesy Insaco)

To address absorption of the substrate of the 1-micron laser light, annealing processes were refined in collaboration with Stanford, resulting in promising reductions. Industrial partners successfully pursued approaches to compensating for inhomogeneity. The notion is to polish a surface, which has features complementing the defects in transmission, on the anti-reflection side of the optic using two different approaches. One (Goodrich) involves a small rotary abrasive tip and an x-y table; the other (CSIRO) uses an ion-milling technique. Both can bring the net optical path seen by the light to an acceptable level. In parallel, manufacturers were able to produce material with improved homogeneity.

The Thermal Noise Interferometer (TNI) research at Caltech produced its first preliminary results with fused silica test masses, and noise hunting and noise reduction is underway.

Optical Coatings

One important measure of the optical coatings is the optical absorption. Acceptable (sub-ppm) losses have been demonstrated this year with conventional coatings by several vendors.

We pursued a strong LSC/LIGO Laboratory program this year to identify the magnitude and source of coating mechanical losses, and to improve the model of the coating thermal noise. The mechanical losses lead to thermal noise; the coating is an important contributor due to the geometry of the test mass, coating, and laser beam, There is a limited choice of materials and of processes which lead to both low mechanical and low optical losses. We are executing a program to identify the source of loss and to explore alternative coating materials and processes that meet the combined optical and mechanical requirements.

Significant progress has been made: We were able to demonstrate the source of the mechanical losses in the coating. The high-index tantalum material, rather than the low-index material or

26 LIGO M030023-00M interfaces, is responsible. We are now pursuing alternative coating materials with several vendors with incremental progress in reducing losses.

Thermal Compensation

The initial prototyping of the two schemes for thermal compensation concluded this year and resulted in the PhD thesis of a LIGO student18. The lens formed in the substrates due to the absorption of the laser light in the substrate make the interferometer sensitive to the power level. Including a thermal compensation system allows the interferometer to be used with a wide range of input powers, allowing e.g., better low frequency sensitivity with a reduction in the power. It also allows a trade to be made with the material properties of the substrate; this is useful for sapphire, and necessary in the fallback case of fused silica.

The basic approach for compensation is to add a complementary additional heat source, so that the sum of the laser and compensation heating leads to a uniform optical path. In one technique, a circular heater adds heat to the edge of the optic. In this way, the scattering effect of lensing can be reduced (in experiments and models, which show excellent agreement) by more than a factor of 50; see Figure 11, upper plots. This is a very effective approach for the case of uniform absorption, which is expected to dominate.

18 R. Lawrence, “Active Wavefront Correction in Laser Interferometric Gravitational Wave Detectors,” MIT Ph.D Thesis, 2002, P030001-00-R

27 LIGO M030023-00M

S =8200 ppm 0 S=120 ppm 2 2

1 1

0 0 y (cm)

1 1

2 2 2 1 0 1 2 2 1 0 1 2 x (cm) x (cm) Ring Compensation

S =6700 ppm 0 S=790 ppm 2 2

1 1

0 0 y (cm)

1 1

2 2 2 1 0 1 2 2 1 0 1 2 x (cm) x (cm) Laser Compensation

Figure 11 Thermal compensation demonstration results. Top left: The contour map for a uniform absorption of a Gaussian beam. Top right: The residual deformation after compensation with a ring heater. Bottom left: the distortion due to a ‘point absorber’ (mimicked by a small probe laser beam); Bottom right: the map after compensation with a scanned compensation beam.

In the second approach, a scanning laser beam is played on the substrate and the dwell time and/or intensity can be modulated to deposit heat in a pattern optimized to compensate for a specific defect, for example a volume of higher thermal absorption. As shown in the lower plots in Figure 11, an additional suppression of a factor of 8 can be achieved for this example of point defect.

Pre-stabilized Laser

The program to develop 200 W laser sources continued at Adelaide, Stanford, and Hanover. During this year, each group has built up a prototype of their approach to making the high-power head: an injection-locked end-pumped rod design from Hanover, an injection-locked stable- unstable slab in Adelaide, and a slab amplifier at Stanford. The near-term goal is to make a selection based on a set of criteria developed at Hanover, one of which is to produce 100 W by February 2003. Greater than 90 W have been produced in several designs, although not in the final configurations; see Figure 12 for an example output curve for a linear resonator using the Hanover approach.

28 LIGO M030023-00M

multimode Resonator( M2 < 7 , OC = 12% )

100 non polarized 90

80

70

fiber10 Xbundle3W852%OClayoptQRics4wihBcamlrPlH 60

50 output[ power W] 40

30

20 50 100 150 200 250 pump power / Head [W] Figure 12 Laser Zentrum Hannover early prototype of a high-power laser head in a linear cavity configuration (at left). The final configuration is a ring-resonator. At right, the power output of the system as a function of the pump light input power; the system approached the initial goal of 100 W.

Input Optics

The University of Florida and their collaborators made progress on the challenges in the Input Optics subsystem. A novel Faraday Isolator design was developed which uses a pair of crystals in a compensation technique to deliver high isolation at high powers. In this design shown in Figure 13, two 22.5° Faraday rotators and a reciprocal quartz polarization rotator placed between them replace the traditional single crystal 45° Faraday rotator. In such a configuration, polarization distortions that a beam experiences while passing the first rotator will be compensated in the second. Tests to the maximum power available are encouraging.

29 LIGO M030023-00M

-20 -25 Conventional FI -30 Isolation -35 Ratio (dB optical) -40 -45 -50 Compensated Design -55 020406080100 Laser Power (W) Figure 13 Top: compensated Faraday isolator design. Bottom: isolation for a conventional and the compensated designs.

We reviewed the Input Optics Design Requirements prepared by the group at the University of Florida, and the group was given approval to proceed to the preliminary design.

Systems and Interferometer Sensing and Control

We refined the baseline design and conducted a System Design Requirements Review. A number of subsystem requirements and trade studies were concluded. We initiated a study of the data readout approach for the signal-recycled interferometer. The preliminary result is that the DC readout (in contrast to the traditional RF-modulation technique) appears to take advantage of the coupling that exists in a signal-recycled interferometer between the shot-noise fluctuations and the photon pressure on the test masses. We have also been working with industry to develop a low noise Digital-to-Analog Converter (DAC). Test results on the first prototypes should be available before the end of this year.

30 LIGO M030023-00M

LIGO Scientific Collaboration (LSC)

The LIGO Scientific Collaboration19 (LSC) is the means for organizing technical and scientific research in LIGO. Its mission is to insure equal scientific opportunity for individual participants and institutions by organizing research, publications, and all other scientific activities.

It includes scientists from the LIGO Laboratory as well as collaborating institutions. The organization is separate from the LIGO Laboratory, with its own leadership and governance, but reports to the Laboratory Directorate for final approval of its research program, technical projects, observational physics publications, and talks announcing new observations and physics results.

The March 2002 LSC meeting was held at the Livingston Observatory. In conjunction, Louisiana State University (LSU) hosted a symposium honoring Bill Hamilton. Numerical relativists with an interest in collaborating with LIGO and LISA made presentations and participated throughout the LSC meeting. LIGO-LSC and the numerical relativists initiated plans for useful activities that will support LIGO observational programs and guide theoretical research.

The eleventh meeting of the LIGO Scientific Collaboration (LSC) was held at the Hanford Observatory August 19-23, 2002. The significance of the upcoming science run and the organization of the subsequent data analysis effort were discussed. The schedule for Advanced LIGO was also presented.

The first science run (S1) included active participation from LIGO Laboratory scientists and staff but also, in numerous ways, from the broader community of scientists composing the LSC. LSC scientists contribute to real-time monitoring of the interferometer data for detector diagnostics and conduct analyses of the data.

The LSC scientists, as members of “upper limits” groups, pioneer the analysis of LIGO data in the search for gravitational waves. Several of these collaborating groups perform real-time searches using computers at the observatories. These searches are useful in providing rapid feedback to the control room on any instrumental pathology that might mimic a true gravitational-wave source.

Keeping the LIGO interferometers running smoothly and continuously requires a cadre of skilled operators at each site, working in teams on rotating shifts. The operators must bring the interferometers into lock, tune the alignment and gains to optimize sensitivity, and try to preserve those optimum conditions. Beyond operating the interferometers, the quality of the science data must be assured. This requires a parallel implementation of scientific monitoring shifts.

LSC scientists have been staffing the scientific monitoring shifts. The scientists or “scimons” focus on ensuring that the interferometer data is of the highest quality. Since scimons start with diverse specialties and backgrounds, formal training was instituted for bringing new participants up to speed. An expert scimon is paired with a “trainee,” a pattern that began back in November 2000. As a result, the pool of scimon experts has steadily increased. This will be essential to support the anticipated periods of steady state, multi-month data runs.

More than 180 eight-hour shifts were staffed by scientists from Caltech, Carleton College, the University of Florida, Hanford Observatory, Livingston Observatory, Louisiana Tech., the University of Southeastern Louisiana, Loyola University, Louisiana State University, the University of Michigan, Massachusetts Institute of Technology, the University of Oregon, Pennsylvania State University, the University of Rochester, Syracuse University, the University of Texas at Brownsville, Washington State University–Pullman, and the University of Wisconsin-Milwaukee.

19 http://www.ligo.org

31 LIGO M030023-00M

Just prior to the start of S1, several of the upper limits groups verified that an emulated gravitational-wave signal could be detected in the data. They simulated the response of the LIGO mirrors to a variety of gravitational waveforms, allowing downstream confirmation that the signal did indeed appear as expected.

We have scheduled the next LSC meeting at Livingston, March 17-20, 2003. At this meeting, results from the S1 data analysis will be discussed; the pre-stabilized laser head downselect will be presented; and a preliminary assessment of sapphire/fused silica test mass downselect data will be made.

32 LIGO M030023-00M

Astrophysics and Data Analysis

The work on astrophysical data analysis is an LSC activity with a strong Laboratory contribution. The present effort is organized into four groups, with the objective of setting interesting upper limits on the flux from short-term burst sources, stochastic sources, binary inspiral ‘chirps’, and for continuous-wave sources.

Searches for Un-Modeled (Burst) Sources

The LSC Bursts Working Group (BWG) pursues the search for gravitational wave bursts in LIGO. The group has more than 40 members from LIGO and the LIGO Scientific Collaboration (LSC). The goal of the BWG is to look for short transients (lasting less than one second) of gravitational radiation of unknown waveform. These include burst signals from supernovae and black hole mergers for which the physics and computational implications are complex enough that make any analytical calculation of the expected waveforms extremely difficult. The detailed knowledge of a signal waveform would have allowed the use of matched filtering which is the optimal detection technique; this is something that falls outside the goals of the BWG and the Inspiral Working Group rigorously pursues it. Only general considerations regarding the duration and the requirement for the signal to have significant strain amplitude in LIGO's sensitive frequency band are made and general time-only domain and time-frequency domain search techniques are employed. These aspects of search strategy make the search for bursts with LIGO open to any unanticipated source of gravitational radiation that falls under the general time-frequency considerations, an issue that should not be neglected in these early stages of gravitational wave astronomy.

An additional focus of the BWG is to look for correlations of gravitational wave bursts with γ-ray bursts (GRBs). A number of GRB progenitors are plausible gravitational wave burst emitters and a comparison of the correlation function of the LIGO detectors immediately before a GRB (“on source”) and at random times (“off source”) may statistically establish their association20.

Finally, the BWG plans to integrate the GEO and LIGO data in a single analysis making the most out of a multi-detector coincidence analysis.

The LIGO S1 run reflects an integrated ~96 hours of coincidence observation with the three LIGO detectors. The gravitational wave channel, AS_Q, was analyzed within the LDAS (LIGO Data Analysis System) environment after it was whitened. Three main astrophysical search algorithms were employed for the detection of bursts; these are referred to as Event Trigger Generators (ETGs) and, technically, they are Dynamical Shared Objects (DSOs) running within LDAS.

The “SLOPE” ETG is a time-domain algorithm (commissioned by Ed Daw and inspired by Arnaud et al.21 that fits the AS_Q time series to a least-squares line and selects candidate events based on the value of the slope. The algorithm reports the start time and significance (value of the slope) of the excursion.

The “TFCLUSTERS” ETG is a time-frequency method (developed and commissioned by Julien Sylvestre22; gr-qc/0210043, to appear in Phys. Rev. D) relying on successive spectrograms taken every 0.125 seconds, which are then thresholded to identify time-frequency tiles (“pixels”) with statistically significant excess of power. These pixels are then clustered and the total power, central frequency, bandwidth, start time and duration of the formed cluster are reported.

20 Finn et al., Phys. Rev. D 60, 12110 (1999) 21 Arnaud et al., Phys. Rev. D 59, 82002 (1999) 22 J. Sylvestre, gr-qc/0210043, to appear in Phys. Rev. D

33 LIGO M030023-00M

A third method, “POWER23” uses like “TFCLUSERS” Fast Fourier Transforms to calculate power spectra of the raw time series for any given start time and duration. The algorithm then compares the power in the data over every user-defined time-frequency tile to the statistical distribution of noise power. A burst signal is detected if the excess of power is greater than expected from the statistical fluctuations of the noise. For each search method the candidate bursts and their features were stored in the LDAS database.

At the same time, a set of interferometer and environmental channels (with insignificant or null coupling to gravitational radiation) were analyzed within the DMT (Data Monitoring Tool) for the identification of transients of non-astrophysical origin, i.e., glitches attributed to the instrument and its environment. Following some high-pass filtering (typically 30Hz cut-off), glitch-finding methods based on time-over-threshold (both in absolute -ADC counts- and relative -sigma- sense) methods were invoked in identifying the start time, duration and significance of non-astrophysical transients. These defined the so-called veto triggers and their temporal coincidence with gravitational wave event triggers resulted in excluding the latter from further consideration. The use of vetoes in the burst analysis pipeline was thus able to reject a fraction of the candidate events at the cost of loss of detector lifetime.

Requiring their temporal coincidence in the three LIGO interferometers attained further reduction of the remaining candidate events. A transient signal of astrophysical origin is expected to yield time-correlated triggers in the three LIGO detectors subject only to the propagation time between the sites and any dispersion introduced in establishing the burst time via the search algorithms. Further correlation in burst duration, frequency band and amplitude as well as that of the raw time series themselves between the sites is to be expected.

So far we have employed only the temporal coincidence of burst triggers across the three LIGO interferometers as well as the frequency band matching for the ETGs performing a time- frequency analysis. The exploitation of the full power of the multi-detector search for bursts is expected to take place in the near future.

A central element in analyzing the S1 data has been the definition of an ~10% of the S1 coincidence data as the “playground” set. In order to avoid any statistical biases in the search for bursts, we have allowed any tuning involved in setting the search algorithm and veto parameters to be performed only on this set. Once this was done, the analysis was applied to the remaining ~90% of the S1 coincidence data.

The bursts analysis pipeline we have just described was applied to the S1 triple-coincidence data and an upper bound on the rate of events observed by the three detectors was established using the unified approach on setting upper limits of Feldman and Cousins24. A full set of Monte Carlo simulations was also used to inject Gaussian and sine-Gaussian signals of variable strength, width and frequency content onto the real interferometer time series. This allowed us to establish the efficiency of the entire bursts analysis pipeline to selected ad hoc benchmark bursts. We were thus able to translate the bound on the event rate to an exclusion plot of fluxes versus strength of gravitational wave bursts originating from fixed strength sources positioned on a fixed sphere centered on earth. These plots will be released as soon as the bursts analysis is internally reviewed and approved by the entire LIGO Scientific Collaboration (LSC). A richer interpretation invoking astrophysics motivated signal waveforms as well as source depth and angular distributions are currently being worked on and will be reported in the near future.

23 Anderson et al., Phys. Rev. D 63, 042003 (2001) 24 Feldman and Cousins, Phys. Rev. D, 57(7), 3873

34 LIGO M030023-00M

Search for a stochastic gravitational wave background

Stochastic backgrounds are signals produced by many weak incoherent sources. They are non- deterministic and can only be characterized statistically. Such signals can arise from early- universe processes (analogous to the electromagnetic CBR) and from present-day phenomena. They give rise to a (probably stationary and Gaussian) signal that is correlated between the two detectors. It will have the same spectrum in each detector, and is differentiated from detector noise by its inter-detector correlation, which depends in a known way on the signal spectrum and the detector separation and orientation. The greatest risk is that similar correlations may be produced by the (electromagnetic) environment.

Stochastic signals are expected to be quite weak compared to the intrinsic noise of an individual LIGO interferometer; consequently, detecting or placing a limit on a stochastic gravitational wave signal will require long observation periods over a bandwidth a few times the inverse light travel time between the interferometers.

Activities of the Stochastic Upper Limit group have centered on the analysis of two data collection runs, the E7 and the S1 science run. During these runs, the LIGO Hanford and LIGO Livingston Observatories recorded coincident data suitable for analysis for stochastic gravitational wave sources. More detailed information is available in the group's E725 and S126 reports. However, vetted science results are not yet available from S1 analysis.

GEO600 also took coincident data with LIGO detectors during the E7 and S1 runs; however, GEO/LIGO correlations are not reported on here. Although a GEO-LIGO correlation will not improve the upper limit by much due to the small overlap between the GEO and LIGO interferometers, it will provide insight about any inter-continental cross-correlated environmental noise. The ALLEGRO27 resonant bar detector took data in three different orientations during E7. Analysis of these data will not be reported on here.

The search for a stochastic background of gravitational radiation in the E7 and S1 data employs the standard optimally filtered cross-correlation technique. We have summarized this procedure in a LIGO technical document28.

For the S1 data analysis, 7.5 hours of triple coincidence (L1-H1-H2) data were set aside for stochastic upper-limit playground analyses. These data were purposely chosen to be scattered throughout S1, and to represent "typical" instrument performance (both bad and good). All investigations that could bias our final upper-limit on the stochastic background signal strength were initially performed on the playground data.

In addition, simulated stochastic background signals were injected into two 1024-sec stretches of post-S1 data in the Hanford 2-km and Livingston-4km interferometers. The hardware injections allowed us to test the full data analysis pipeline-from mirror movement to upper-limit values-for large SNR signals where we knew (a priori) the expected results.

In an actual search for a stochastic background signal, we work with discretely sampled data broken up into segments T = 90s in length. Within the LIGO data analysis system (LDAS), we request the gravitational wave data in 15-minute chunks (each 15-minute chunk representing a single job), originally sampled at 16384 Hz. We then down-sample the data to 1024 Hz for LHO-

25 http://www.phys.utb.edu/stochastic/, "E7 report" 26 http://www.phys.utb.edu/stochastic/, "S1 report'' 27 W. O. Hamilton et al., "Resonant detectors and interferometers can work together," Proceedings of the SPIE conference, Hawaii, 2002. 28 “Detecting a Stochastic Background of Gravitational Radiation - Background Information,” LIGO Technical Document, http://www.ligo.caltech.edu/docs/T/T020166-00.pdf.

35 LIGO M030023-00M

LLO correlations (2048 Hz for H1-H2 correlations), and estimate power spectra for each detector, which are used in the calculation of the optimal filter for a stochastic background with Ωgw(f) = const := Ω0.

Within the stochastic search code, we calculate instrument response functions, which are valid for the particular job we are analyzing. We then split the data into 10 (90-second) segments, each of which is windowed in the time domain, zero-padded to twice its length, and discrete Fourier- transformed. A value of the optimally filtered cross-correlation statistic is calculated for each T = 90-sec segment, while the theoretical variance is calculated only once for the whole 15-minute job. For each 15-minute job, we calculate the sample mean, and sample standard deviation of the 10 cross-correlation statistic values. Finally, we then form a weighted average to obtain a point estimate of the stochastic background signal strength. Frequentist methods are used to convert 2 the composite cross-correlation measurements to limits on Ωgw(f)×h100 .

As an example of the expected 90% confidence level upper-limits for a pair of LIGO interferometers, we consider H2-L1. An upper-limit was calculated, solving for Ωgw(f) = const in the 40Hz - 265Hz frequency range, with SNR set to 1.28 (for 90% confidence), and typical S1 power spectra substituted for P1f) and P2(f). The observation time (corresponding to the amount of clean, coincident H2-L1 S1 locked data) was 100h, resulting in an expected upper limit of 2 Ωgw(f) x h100 < 15. This serves to set the scale of expected performance for the LIGO interferometers during the S1 run.

Simulated stochastic background signals with Ωgw(f) = const were injected into two 1024-sec stretches of post-S1 data in the LHO and LLO interferometers (so-called hardware injections). 2 Ωgw(f) x h100 = 24414 and 3906 for these two injections, corresponding to SNRs of roughly 10 and 5 in a 15-minute observation. The effect of these two hardware injections on the power spectral densities of the interferometers is evident as excess noise in the injected frequency band.

2 Averages of the point estimates of Ωgw(f) x h100 as produced by the stochastic DSO analysis software for the times of the hardware injections fall within one or two standard errors of the injected point estimate, giving us confidence that the full data analysis pipeline is working as expected.

In addition to performing the hardware injections, we are able to inject via software simulated stochastic background signals into the data. Functionality exists within LAL to simulate stochastic α signals (with power law dependence Ωgw(f) = f ) for the LHO and LLO interferometers, convolved with the appropriate instrument response functions. Results of the stochastic DSO analysis of software injections were consistent with that of the hardware injections, up to an overall sign. It is interesting to note that this comparison of hardware and software injections first discovered an overall sign difference between the interferometer transfer functions of LHO and LLO, which was subsequently measured and confirmed at the sites.

Production analyses are ready to be performed. Preliminary analyses were based on a static amplitude calibration for the gravitational wave channel, one that ignored the fluctuations in optical gain in the differential-arm control loop. These calibration data are now available for all three LIGO interferometers, so that production analyses can commence.

We are also studying a hierarchical approach in collaboration with IUCAA, Pune, India. We have defined and prototyped an improved hierarchical scheme in searching for inspiraling binaries. The earlier hierarchical scheme developed by Mohanty and Dhurandhar used the two masses of the constituent stars for implementing the hierarchy. This scheme is being currently implemented into LAL in order to make the algorithm available for the next phase of LIGO science runs. The improved scheme extends the hierarchy to yet another parameter, namely, the time-of-arrival, so that the hierarchy is now in three parameters. This procedure is expected to reduce the cost by a

36 LIGO M030023-00M factor of 4 or 5 over the Mohanty-Dhurandhar search and by a factor of about a 100 over the flat search. The algorithm and its prototyping results have been discussed in several conference proceedings29,30 and is pending publication31.

Search for Binary Inspiral signals

The Inspiral Upper Limit Working Group is focussed on the search for gravitational-wave “chirps” emitted by compact binary systems as the bodies spiral ever closer to one another and ultimately coalesce. The group’s charter is to extract astrophysically significant results (presumably upper limits rather than detections) from early LIGO data, collected while the detectors have modest sensitivity. So far, the group has focused on low-mass systems, including binary neutron star systems (in which each body is expected to have a mass of ~1.4 solar masses).

We search for gravitational wave signals from binary inspirals in the LIGO data using matched filtering. This method uses linear filters constructed from the expected waveforms that are computed using post-Newtonian methods. The waveforms used to generate the filters in this analysis are the stationary phase approximation to the Fourier transform of the second post- Newtonian order. We neglect spin effects and and use the restricted approximation described in. This gives a two parameter family of waveforms; the parameters being the masses of the objects in the binary system. We further restrict the binary systems to circular orbits. These waveforms are known as 2pN inspiral chirps.

The group began its work in earnest in early 2002, using data from the E7 engineering run to develop data analysis procedures and to explore ways of using environmental and instrumental auxiliary channels to identify transient disturbances in the detectors, in order to “veto” false gravitational-wave candidates. One of the key concepts introduced was to set aside a small fraction of the data as a “playground” in which analysis cuts and veto conditions can be studied and tuned freely; then, after freezing all details of the analysis, the final result can be extracted from the remainder of the data without fear of human bias. The main gravitational-wave inspiral search uses the standard technique of optimal Wiener filtering with a bank of inspiral templates covering the mass parameter space of interest, utilizing code from the LIGO Algorithm Library (LAL) and using the job control, data conditioning, parallel processing, and database functionality provided by the LIGO Data Analysis System (LDAS). In addition, an exploratory analysis was done using the Fast Chirp Transform (FCT) algorithm running within LDAS.

In September, the focus of the group naturally shifted to the greatly improved data from the S1 science run, in which binary-neutron-star inspiral signals are detectable to a greater distance than ever before.

Matched filtering requires a good set of template waveforms that accurately predicts the possible signals. Ideally the signal from a binary inspiral would be computed from an exact two-body solution to the Einstein equations for the general relativistic gravitational field. However, the exact two-body solution is not known and one must use some kind of approximation. We use the restricted second-post-Newtonian (2PN) Taylor-series approximation to waveforms for nonspinning compact (point) objects in quasi-circular orbits. Restricted 2PN means that the amplitude is computed only to leading order in GM/rc2 (where M is the total mass and r is the orbital separation in harmonic coordinates), while the phase evolution of the waveform is computed to two orders in GM/rc2 beyond leading order. The waveform phase can be approximated, in this case by a Taylor series, in either the time domain or the frequency domain. Since the difference between these two approximations can give us some idea of the errors due to the failure of the post-Newtonian approximation in the late stages of inspiral, we use both:

29 Amaldi Conference 2000. 30 GWDAW 2002 31 http://www.ligo.caltech.edu/docs/P/P020015-01.pdf

37 LIGO M030023-00M

The template bank and the actual templates used to filter the data are constructed using the frequency-domain approximation, and the injected waveforms used to test the efficiency of the analysis use the time-domain approximation.

As an additional pathology check, we compute the overlap of each template — put into the frequency domain with a discrete FFT — with a stationary-phase approximation of itself in the frequency domain. Since the stationary phase approximation is known to go bad only when the post-Newtonian expansion goes bad, this is an independent and tighter check that sidesteps issues of time-domain vs. frequency-domain approximations. We find that the overlap is below 90% for binaries of M > 2.5Mo with the H2 noise curve and much better for the others. The physical reason for this is that the frequency of the last circular orbit, about when the merger waveform begins, is in the interferometer’s sensitive band for such high masses.

The IUL detector characterization sub-group initially considered all control channels and all PEM channels as possible sources for vetoes. The approach adopted for S1 built upon experience developed during the E7 analysis. Numerous software tools were used to examine the data; DMT programs, home made MATLAB scripts, and examination by eye using DTT. In the E7 analysis there was much hope that a smoking gun would be found among the PEMs. Virtually all of the accelerometer, seismometer, microphone, and voltage line monitor and magnetometer channels were examined. After a careful search, however, we found that the inspiral-template-based L1: LSC-AS I veto (the interferometer antisymmetric output signal, demodulated at 90 degrees to the strain channel) does the best job with moderate dead time.

The group is now in the process of refining the analysis, especially in the areas of applying appropriate auxiliary-channel vetoes and modeling the spatial distribution of sources in the Milky Way, so that the efficiency of the search can be calculated accurately. The group expects to publish at least one result in 2003 based on the S1 data.

Search for Periodic signals

The primary astrophysical candidates for periodic emission of gravitational waves are spinning neutron stars, either isolated or in binary systems. Continuous gravitational waves are emitted from these candidates when there are asymmetries due to either rotation about a nonsymmetry axis, precession, or stellar pulsations. A subset of these objects is observed in the electromagnetic spectrum, for example as pulsars or in x-ray binary systems. A further subset of these objects spin fast enough to put their potential gravitational wave emission frequency into the LIGO and GEO band. (For the simplest case the gravitational wave frequency is emitted at twice the spin frequency). However, there should be many more neutron stars than those observed, and there is always the possibility of an unknown class of periodic sources. Thus, both targeted and untargeted searches are warranted. Targeted searches include known pulsars, for which the position, spin frequency, and spin evolution are known, and low-mass x-ray binaries, for which the position is known, but a search over a limited frequency band and orbital parameters is needed. Targeted searches could also include a targeted set of positions on the sky (such as that of a globular cluster or the galactic center) for which a search over the other signal parameters is needed. Untargeted searches involve a search over many sky positions and intrinsic source parameters. Note that in addition to intrinsic source evolution, the changing velocity and orientation of the detector relative to the source induces amplitude and phase modulations into the data. And since periodic signals are expected to be weak, long observation times are required for detection. An untargeted search is very interesting, but doing so using coherent techniques (i.e., tracking the phase of the signal, such as in matched filtering) is computationally expensive in terms of the required CPU cycles. Incoherent and hierarchical methods must be used to make the untargeted searches feasible. Note that all incoherent and hierarchical searches invoke coherent methods as part of their strategies. Targeted searches using coherent techniques are computationally affordable and relatively easy to implement compared with untargeted searches. Targeted searches are of interests in their own right, but

38 LIGO M030023-00M also much of the code developed for a targeted search can be used in an untargeted search as well, making this an important first step in that direction. The groups’ proposal for the initial analysis of LIGO and GEO data was crystallized by August of 2001.

Much of the coding, testing, and the first analysis of science data took place during the period covered by this report. In the last year PULG has consider four types of searches. Each search is described briefly below.

Time Domain Searches for Signals from Known Isolated Pulsars

The time domain analysis is based around the idea of heterodyning—unwinding the expected phase of the pulsar signal by multiplying (mixing) the data with a complex function of the form exp(-2π ift), where f is the expected frequency of the gravitational wave signal. The procedure is done in several steps of heterodyning, filtering, and down sampling of the data. This reduces the volume of data by factors of about 106, which is of great practical importance in data management. If carried out with the right pulsar timing parameters, the only time-varying quantity remaining in the signal left in the data is the antenna pattern of the interferometer, which varies on timescales of a day. The procedure should, by the central limit theorem, give the noise a near- Gaussian probability density. This is checked very carefully, and if satisfied, the probability of the data for sets of signal parameters is found using chi-squared. Standard Baysian statistical techniques are used to assign posterior probabilities to the parameters. Using fake data and injections of fake signals into real data has validated this code. This code has been used in the preliminary analysis of LIGO and GEO S1 data.

Frequency Domain Searches For Signals from Known Isolated Pulsars

The frequency domain analysis is being implemented both as a stand-alone code and as a DSO under LDAS. Both the stand-alone code and a stand-alone version of the DSO have also been used as a test-bed for distributed grid computing under the GriPhyN project the DSO in conjunction with LDAS. Both realizations use match filtering to coherently sum the data to extract the signal, correcting for phase and amplitude modulation. The output of the matched filtering code is the optimal statistic, defined as the F-statistic; F is derived using the principle of maximum likelihood. The scheme involves two steps. Step 1 is to split the observation time into shorter segments and generate a Short-time Fourier Transform (SFTs) for each segment using ordinary FFT routines. Step 2 is to input the SFT data for a narrow frequency band of interest from all the SFTs that cover the observation time and to send this data into the LAL functions that calculate the F-statistic. A Monte Carlo simulation that injects signals into the real data finds the distribution of F, and classical statistical analysis is used to find confidence intervals or upper limits on the signal amplitude. (The estimated parameters that maximize F can also be computed; this has not yet been implemented.) Some Monte Carlo simulations have been completed. This code has been used in the preliminary analysis of LIGO and GEO S1 data.

Blind Unbiased Incoherent Searches

An “unbiased” all-sky search for sources of periodic gravitational radiation is under way. It is unbiased in the sense that few assumptions are made about the nature of the sources. In particular, no attempt is made to track the phase of such a source over extended time intervals. The technique used is based on incoherent averaging of one-sided power spectral density estimates, that is, on averaged periodograms. Incoherent averaging is generally less sensitive to weak sources than is coherent integration, but its reduced computational load permits a search over the entire sky, and the phase-insensitivity of power averaging makes the technique robust against uncertainties in source parameters. A statistically independent determination of background noise level is found using nearby (but not quite neighboring) bands to a given narrow frequency search range. Regions of the spectrum with sharp features, e.g., near a 60 Hz

39 LIGO M030023-00M harmonic will be excluded from consideration or handled (in the long term) with a more sophisticated algorithm. The effects of the modulations will be determined empirically and parameterized, as detection efficiency corrections, using Monte Carlo software signal injections. This search makes use of the SFTs generated for search 2 above. This search method has been used in the preliminary analysis of LIGO and GEO S1 data.

Targeted Search for a Signal from the Pulsar in the Binary System ScoX1

The accretion of hot material onto the surface of a neutron star was suggested over 20 years ago as a possible mechanism to generate quasi-monochromatic gravitational waves. In this scenario the induced quadrupole moment is directly related to the accretion rate (which can be copious) allowing the gravitational energy reservoir to be continuously replenished: gravitational radiation balances the torque due to accretion.

Such scenario has attracted considerable new interest in the past few years and has been fully revitalized by the launch of the Rossi X-ray Timing Explorer, designed for precision timing of accreting NS’s. The observational evidence that Low Mass X-ray Binaries (LMXBs) - binary systems where a compact object accretes material from a low mass companion — in our Galaxy are clustered around a rotation frequency ~ 300 Hz, led Bildsten to propose a mechanism to explain this behavior. The fundamental idea is that continuous emission of GW’s radiates away the angular momentum that is transferred to the NS by the infalling material. The fact that the rate of angular momentum loss through GW’s scales as f^5, provides a very natural explanation for the clustering of rotation frequency of several sources. The physical process responsible for producing a net quadrupole moment is the change of composition in the NS crust, which in turn is produced by the temperature gradient caused by the in-falling hot material.

Recently, Ushomirsky et al 32. have posed this initial idea on more solid theoretical grounds. More recently Wagoner has argued that LMXBs could reach a stable equilibrium state by emitting GW through r-modes, allowing GWs from Sco X-1 and other LMXBs to be potentially detectable by advanced LIGO. If one of these mechanisms does operate, LMXBs are extremely interesting candidate sources for Earth-based detectors. Several systems would be detectable by advanced LIGO, if the detector sensitivity is tuned, through narrow-banding, around the emission frequency. In particular, Sco X-1, the most luminous X-ray source in the sky, might be marginally detectable by “initial” LIGO, and GEO600 (the latter in narrow-band configuration), where an integration time of approximately 2 years would be required.

The implementation of the data analysis scheme follows the frequency domain search for known pulsars. Code has been developed which generalizes LALDemod in order to take into account the orbital motion of the source. This code represents the core of the search together with a function designed to place filters in the space defined by the orbital parameters. At present the code implementation allows us to search only for binary systems in circular orbits. Some effort is on-going to generalize the codes to handle the more general case of binaries with nonzero eccentricity.

32 http://www.arxiv.org/abs/astro-ph/0210175 and references therein

40 LIGO M030023-00M

Outreach

During 2002, the LIGO Laboratory has worked with Jill Andrews (Caltech Assistant to the Provost for Educational Outreach) and NSF program director Beverly Berger to plan an enhancement of existing LIGO Laboratory outreach efforts. LIGO has already conducted an impressive range of local educational outreach activities at both its Observatories33.

To leverage previous successful NSF-funded education and outreach (E&O) program experience, each Observatory Head is recruiting local educators and community leaders who form a “Local Educators’ Network” (LEN). Focus groups and, as necessary, a more permanent advisory group will be recruited from the larger group of LEN participants. All existing or planned activities will undergo assessment in the context of relevance and feasibility by Observatory Heads with their LEN focus groups. The goal is to develop and maintain long-term, interactive partnerships to inspire, excite, and motivate a broad spectrum of learners through inquiry, exploration and experience in science and engineering research. With collective input from our LEN focus groups (which we expect to underscore outcomes from similar efforts based at Caltech and other universities) LIGO Observatory Heads will implement a plan that features a balanced set of LIGO- related educational activities, programs and products with broad impact in formal education, informal education, and public learning venues.

In November 2002, LIGO presented updated plans NSF. We are submitting a proposal to the MPS Internships in Public Science Education (NSF 01-39) for continued and supplemental support of existing and/or new programs in three main areas. These are:

1. Formal Education: Internships in Public Science Education. We plan to seek funds in order to continue hosting science educators at each Observatory. These educator interns work with LIGO researchers in developing resource materials and products that both capitalize on LIGO science and satisfy the needs of local educators. 2. Informal Education: To reach broader audiences, we will seek supplemental resources and form partnerships in the local communities to create museum-quality exhibits in each Observatory. We will work to reach teachers and students who are unable to visit the Observatories by pursuing the resources necessary to create a “Mobile Science Unit,” and will seek out community youth programs already in place to enhance their programs with our people and products. 3. Public Outreach: We are planning products such as educational videos for Television, radio public service announcements or “spots,” and a more interactive website.

Educational Outreach – Hanford

LIGO Hanford Observatory has contributed to the expansion of high-school science education by directly involving students in LIGO research. This year approximately 70 students from Gladstone High School (in northwest Oregon) worked on LIGO-related projects throughout the academic year. On May 28, 2002, students from grades 9-12 described their contributions to LIGO research to a packed audience of community members at Gladstone High School. (See story at http://www.ligo.caltech.edu/LIGO_web/0205news/0205han.html for additional details.)

In the summer, a high-school teacher and a middle-school teacher held visiting appointments at the observatory, helping us to develop in-classroom and informal educational resources. This work has been disseminated using the "teachers corner" web pages (http://www.ligo- wa.caltech.edu/teachers_corner/teachers.html at LIGO Hanford Observatory.

33 LIGO NSF Proposal for Continuing Operations 2002-2006 (Dec 2000), pgs 24, 84, 165, http://www.ligo.caltech.edu/docs/M/M000352-00.pdf

41 LIGO M030023-00M

A special emphasis was put on science and math lesson plans in both high-school and middle- school versions, that not only include plans, activities and worksheets, but also the web pages (http://www.ligo-wa.caltech.edu/teachers_corner/lessons.html) highlight lesson-plan alignment to the state education standards for Oregon and Washington.

The observatory hosted five undergraduate research students through the REU/SURF program this summer. Eric Adelberger (University of Washington) gave the LIGO Public Lecture this summer, entitled "How Many Dimensions Are There to the Universe?” to an enthusiastic audience of approximately 225 people, ranging in age from pre-teens to retirees.

Approximately 600 visitors toured the observatory this year.

We have formed a Local Educators Network to advise us on future outreach effort. This group consists of teachers and education professionals, members associated with museums and other informal education activities, and people actively working with Native American and Hispanic groups. Educational Outreach -- Livingston

We continue to be involved in a wide range of educational outreach activities aimed at communicating to the public what we do in LIGO. Approximately 2000 students and teachers visit the LIGO site each year as part of school sponsored field trips, and about 1000 adult visitors also tour the site as part of community and professional groups and as informal participants in weekly tours for the general public.

We have implemented a summer Research Experiences for Teachers (RET) program that provides opportunities for teachers to participate in the research activities at Livingston and simultaneously to develop materials and plans that they can take back to their home schools.

Our Research Experiences for Undergraduates (REU) program continues to grow. This year we hosted seventeen students participating in Caltech’s “SURF” program or similar REU or summer programs at LSC member institutions.

We have also hosted several regional workshops for teachers in order to enhance our interactions with K-12 educators in the region.

LIGO Laboratory and Southern Louisiana University (SLU) exchanged a Memorandum of Understanding (MOU). LIGO effort at SLU includes improvements of the LIGO end-to-end model (e2e), and the use of e2e simulation in the education outreach. Prof. Yoshida and his students have been measuring seismic spectra at the LIGO Livingston Observatory, vital information for the LIGO simulation. They are analyzing the measured data using the e2e simulation package to extract more fundamental data for e2e use and to understand the noise due to the beam jitter caused by mirror motions before the recycling mirror.

42 LIGO M030023-00M

Advanced LIGO Project Book

1. Overview

Insert costs and schedule

Following the initial LIGO scientific observation period, planned for 2003 through 2006, LIGO detector systems will require an upgrade to significantly improve the detection sensitivity. Such staged improvements were a central part of the original LIGO design and program plan34.

LIGO consists of conventional facilities and the interferometric detectors. The LIGO facilities (sites, buildings and building systems, masonry slabs, beam tubes and vacuum equipment) have been specified, designed and constructed to accommodate future advanced LIGO detectors. The initial LIGO detectors were designed with technologies available at the initiation of the construction project. This was done with the expectation that they would be replaced with improved systems capable of ultimately performing to the limits defined by the facilities.

In parallel with its support of the initial LIGO construction, the National Science Foundation (NSF) initiated support of a program of research and development focused on identifying the technical foundations of future LIGO detectors. At the same time, the LIGO Laboratory35 worked with the interested scientific community to create the LIGO Scientific Collaboration (LSC) that advocates and executes the scientific program with LIGO36.

The LSC, which includes the scientific staff of the LIGO Laboratory, has worked to define the scientific objectives of upgrades to LIGO. It has developed a reference design and an enhanced R&D program plan. This development has led to this proposal for construction of the Advanced LIGO upgrade following the initial LIGO scientific observing period.

In this Advanced LIGO Project Book, the definition and conceptual program plan for construction of Advanced LIGO are described. It is intended that this Project Book will be developed further and formally maintained as a working baseline definition document for Advanced LIGO.

34 LIGO Project Management Plan, LIGO M950001-C-M (http://www.ligo.caltech.edu/LIGO_web/ligolab/m950001-c.pdf); LIGO Lab documents can be accessed through the LIGO Document Control Center (http://admdbsrv.ligo.caltech.edu/dcc/) 35 LIGO Laboratory Charter, LIGO http://www.ligo.caltech.edu/docs/M/M010213-01/ (http://www.ligo.caltech.edu/LIGO_web/ligolab/charter.html) 36 http://www.ligo.org/charter.pdf

43 LIGO M030023-00M

2. Reference Design Baseline Definition

The LIGO Scientific Collaboration, through its Working Groups, has worked with the LIGO Laboratory to identify a reference design for the Advanced LIGO detector upgrade. The reference design represents a dramatic improvement over the initial complement of LIGO instruments. The reference design is planned to lead to a quantum noise limited interferometer array with considerably increased bandwidth and sensitivity.

The basic optical configuration is a power-recycled and signal-recycled Michelson interferometer with Fabry-Perot “transducers” in the arms; see Figure 14. Using the initial LIGO design as a point of departure, the Advanced LIGO requires the addition of a signal-recycling mirror at the output “dark” port, and changes in the RF modulation and control systems. This additional mirror allows the gravitational wave induced sidebands to be stored in the arm cavities or extracted (depending upon the state of “resonance” of the signal recycling cavity), and allows one to tailor the interferometer response according to the character of a source (or specific frequency in the case of a fixed-frequency source). For wideband tuning, “quantum noise” dominates the instrument noise sensitivity at most frequencies (see FIGURE NOISE ANATOMY OF ADV LIGO). REFERENCE JUST BEFORE THIS IS BROKEN Additional details may be found in Section 12. Interferometer Sensing and Controls Subsystem (ISC)37.

37 Please see http://www.ligo.caltech.edu/LIGO_web/docs/acronyms.html for a dictionary of acronyms

44 LIGO M030023-00M

SA PP HIRE, 31.4 CMφ, 40 KG

SILICA, HE RA EU S SV 35 CMφ 4 KM

SILICA, INITIAL LIGO GRADE INPUT MODE 28.5CM φ CLEANER

ACTIVE T=0.5% THERMAL ARM CAVITY CORRECTION

125 W LASER MOD. BS 830KW PRM ITM ETM T~6%

SRM T=5% POWER &

SIG NA L RECYCLING OUT PUT MODE CAVITIES CLEANER

PD

GW READOUT

Figure 14 Schematic of an Advanced LIGO interferometer, with representative mirror reflectivities optimized for neutron star binary inspiral detection. Several new features compared to initial LIGO are shown: more massive, sapphire test masses; 20× higher input laser power; signal recycling; active correction of thermal lensing; an output mode cleaner. (ETM = end test mass; ITM = input test mass; PRM = power recycling mirror; SRM = signal recycling mirror; BS = 50/50 beam splitter; PD = photodetector; MOD = phase modulation). Mode-matching and beam-coupling telescopes not shown.

The laser power is increased from 10 W to 100-200 W, chosen to be optimal for the desired interferometer response, given the quantum limits and limits due to available optical materials. The resulting circulating power in the arms is roughly 0.5 MW, in comparison with the initial LIGO value of ~10 kW. The Nd:YAG pre-stabilized laser design resembles that of initial LIGO, but with the addition of a more powerful output stage; see Section 8. Prestabilized Laser Subsystem (PSL)). The conditioning of the laser light also follows initial LIGO closely, with a ring-cavity mode cleaner and reflective mode-matching telescope, although changes to the modulators and isolators must be made to accommodate the increase in power; see Section 9. Input Optics Subsystem (IO)).

Whereas initial LIGO uses 25-cm diameter, 11-kg, fused-silica test masses, the test mass optics for Advanced LIGO are larger in diameter (~32 cm) to reduce thermal noise contributions and more massive (~-40 kg) to keep the radiation pressure noise to a level comparable to the suspension thermal noise. Two materials are under study: sapphire and fused silica, and both can be configured to lead to a satisfactory LIGO upgrade. The baseline choice for the core optics substrate material is sapphire. Sapphire promises superior sensitivity for the measured material parameters, and full-size samples are now under characterization. The beamsplitter and other suspended optics, where thermal noise is less important, are made of fused silica. Polishing and coating are not required to be significantly better than the best results seen for initial LIGO; see Section 10. Core Optics Components (COC). Compensation of the thermal lensing in the test mass optics (due to absorption in the substrate and coatings) is added to handle the much-

45 LIGO M030023-00M increased circulating power – of the order of 1 MW in the arm cavities; see Section 11. Auxiliary Optics Subsystem (AOS)

The test mass is suspended by fused silica ribbons or tapered fibers attached with hydroxy- catalysis bonds, in contrast to the steel wire sling suspensions used in initial LIGO. Fused silica has much lower loss (higher Q) than steel, and the fiber geometry allows more of the energy of the pendulum to be stored in the earth’s gravitational field while maintaining the required strength, thereby reducing suspension thermal noise. The resulting suspension thermal noise is anticipated to be less than the radiation pressure noise and comparable to the Newtonian background (“gravity gradient noise“) at 10 Hz. The complete suspension has four pendulum stages, and is based on the suspension developed for the UK-German GEO-600 detector. The mechanical control system relies on a hierarchy of actuators distributed between the seismic and suspension systems to minimize required control authority on the test masses. The test mass magnetic actuators used in the initial LIGO suspensions are eliminated (to reduce thermal noise and direct magnetic field coupling from the permanent magnet attachments) in favor of electrostatic forces for locking the interferometer and photon pressure for the operational mode. The much smaller forces on the test masses reduce the likelihood of compromises in the thermal noise performance and the risk of non-Gaussian noise. Local sensors (electrostatic and occultation) and magnets/coils are used on the top suspension stage for damping, orientation, and control; see Section 7. Suspension Subsystem (SUS).

The isolation system is built on the initial LIGO piers and support tubes but otherwise is a complete replacement, required to bring the seismic cutoff frequency from ~40 Hz (initial LIGO) to ~10 Hz. RMS motions (dominated by frequencies less than 10 Hz) are reduced by active servo techniques, and control inputs complement those in the suspensions in the gravitational-wave band. The attenuation offered by the combination of the suspension and seismic isolation system eliminates the seismic noise contribution to the performance of the instrument, and for the low- frequency operation of the interferometer, the Newtonian background noise dominates. See Section 6. Seismic Isolation Subsystem (SEI).

46 LIGO M030023-00M

Reference Design Parameters

The Advanced LIGO reference design is summarized in Table 1.

Table 1 Principal parameters of the Advanced LIGO reference design with initial LIGO parameters provided for comparison

Subsystem and Parameters Advanced LIGO Initial LIGO Reference Implementation Design Comparison With initial LIGO Top Level Parameters Observatory instrument lengths; LHO: 4km, 4km; LHO: 4km, 2km; LHO = Hanford, LLO = Livingston LLO: 4km LLO; 2km Strain Sensitivity [rms, 100 Hz band] 8×10-23 10-21 Displacement Sensitivity [rms, 100 Hz band] 8×10-20 m 4×10-18 m Fabry-Perot Arm Length 4000 m 4000 m Vacuum Level in Beam Tube, Vacuum <10-7 torr <10-7 torr Chambers Laser Wavelength 1064 nm 1064 nm Optical Power at Laser Output 180 W 10 W Optical Power at Interferometer Input 125 W 6 W Optical power on Test Masses 800 kW 30 kW Input Mirror Transmission 0.5% 3% End Mirror Transmission 15 ppm 15 ppm Arm Cavity Power Beam size 6 cm 4 cm Light Storage Time in Arms 5.0 ms 0.84 ms Test Masses Sapphire, 40 kg Fused Silica, 11 kg Mirror Diameter 32 cm 25 cm Test Mass Pendulum Period 1 sec 1 sec Seismic/Suspension Isolation System 3 stage active, Passive, 5 stage 4 stage passive Seismic/Suspension System Horizontal ≥10-12 (10 Hz) ≥10-9 (100 Hz) Attenuation

Reference Design Sensitivity Goal

The anticipated improvement in the performance of the reference design detector for wideband tuning is indicated in Figure 14 (equivalent strain noise as a function of frequency). This instrument is designed to deliver an improvement over initial LIGO in the rms noise and limiting sensitivity by a factor of more than 10 over a very broad frequency band. This translates into an increase of event rate by more than 1000 for extragalactic sources, so that several hours of operation will exceed, in physics reach, the integrated observations of the 1-year initial-LIGO

47 LIGO M030023-00M

Science Run. These Advanced LIGO interferometers will also have a greater frequency range with both a reduced lower cutoff (10 Hz vs. 40 Hz) and a better high frequency performance (~8 times greater in frequency for comparable sensitivity). Finally, they will have the capability for a reshaping of the noise curve. This allows e.g., narrowbanding with much enhanced sensitivity near some chosen frequency as shown in Figure 15.

1/2 10-22 h(f)/Hz O IG l L tia ini

10-23

gr

av

i t y

gr

ad Equivalent strain noise, Equivalent strain noise,

i ent Susp. thermal

s -24 Internal thermal 10 Quantum noise Total noise

101 102 103 104 Frequency (Hz)

Figure 15 Noise Anatomy of Advanced LIGO. This model of the noise performance is based on our current requirements set, and represents the principal contributors of the noise and the least-squares sum of those components expressed as an equivalent gravitational wave strain.

At the initial LIGO sensitivity, it is plausible but not probable that gravitational waves will be detected. With Advanced LIGO it is probable to detect waves from a variety of sources and extract rich information from them. Specifically (cf., Figure 16), Advanced LIGO is capable of the following science:38

• Inspiraling neutron star (NS) and black hole (BH) binaries: 1.4 MO• NS+NS binaries will be detectable to a distance of 300 Mpc (estimated event rate ~2/yr to 3/day); 1.4 MO• NS+10 MO• BH, detectable to 650 Mpc (estimated ~1/yr to 4/day); 10 MO• BH+BH, detectable to redshift z=0.4 (estimated ~1/mo to 30/day – if black holes form in completely symmetric events, then none will be seen, but this possibility is actually not supported by current astronomical observations). The inspiral waves will reveal the bodies’ masses and spins and will enable precision tests of general relativity at far higher

38 For details see, e.g., C. Cutler and K. Thorne, “An Overview of Gravitational-Wave Sources”, http://xxx.lanl.gov/abs/gr-qc/0204090 and the many references cited therein.

48 LIGO M030023-00M

post-Newtonian order than is possible today [6 orders higher in (orbital speed) /(speed of light).] New relativistic effects will be seen, e.g., radiation reaction due to tails of waves and perhaps even tails of tails. • Tidal disruption of a NS by a BH: When the NS in a NS+BH binary nears its black-hole companion, it can be torn apart by the hole’s spacetime curvature. The disruption waves should carry information about the NS structure and equation of state. Extracting this information will require three interferometers: two operating in wideband mode to measure the inspiral waves and deduce from them the BH and NS masses and spins, and one with noise curve optimized for the high-frequency (~300 to ~1000 Hz) disruption waves. This 3-interferometer configuration can also seek NS equation-of-state information by measuring the influence of tidal coupling on the wave spectrum from inspiraling NS+NS binaries. • BH+BH mergers and ringdowns: When rapidly spinning BH’s collide, they should trigger large-amplitude, nonlinear oscillations of curved spacetime around their merging horizons. Little is known about the dynamics of spacetime under these extreme circumstances; we can learn about it by comparing LIGO’s observations of the emitted waves with supercomputer simulations. Advanced LIGO can detect the merger waves from BH binaries with total mass as great as 2000 MO• , to cosmological redshifts as large as z=2. • Supernovae: Empirical evidence suggests that neutron stars in type II supernovae receive kicks of magnitude as large as ~1000 km/s. These violent recoils imply the supernova’s collapsing-core trigger may be strongly asymmetric, emitting waves that might be detectable out to the Virgo cluster of galaxies (event rate a few/yr) and perhaps beyond. Even when the collapse is spherical and emits no waves, the collapsed core (proto-neutron star) is predicted to be unstable to convective overturn. The gravitational waves from this convection may be detectable throughout our Galaxy and its orbiting companions, the Magellanic Clouds. By cross correlating the gravitational waves with neutrinos from just one such (very rare) event, we could learn much about the proto- neutron star’s convecting core. • Gamma-ray bursts: The triggers of gamma ray bursts are thought to be the collapse of massive stellar cores (hypernovae) and/or the merger of NS+NS or NS+BH binaries, all of which emit strong gravitational waves. The next generation of orbiting gamma-ray telescopes will be operational in the time frame of Advanced LIGO, providing astrophysical triggers for LIGO’s searches. With the aid of these triggers, and with predicted enhancements of the gravitational waves along the burst’s beaming direction (toward earth), estimates suggest coincident detections of a few per year. Any such detection would reveal the nature of the gamma-burst trigger. The third interferometer, with noise curve reshaped for better sensitivity at high frequencies, may enable observations of the trigger’s dynamics. • Spinning neutron stars: The narrowband tunability of the third interferometer will be exploited to search with high sensitivity at high frequencies for gravitational radiation arising from spinning NS’s: known pulsars and Low-Mass X-Ray Binaries (LMXB’s), and unknown pulsars. If (as is plausible) a NS’s accretion torque, in an LMXB, is counterbalanced by its gravitational radiation-reaction torque, then its wave strength is predictable from the observed X-ray flux, and about 10 known LMXB’s would be detectable by Advanced LIGO with narrow-banding (the dots near the minimum of the narrow-band curve) but only one (Sco X-1, the star in Figure 16) without narrow-banding. These LMXB’s may serve as “calibration sources” for LIGO. A NS’s crustal shear or internal magnetic field is predicted to be able to support non-axisymmetric ellipticities as large as ε~10-6 or even 10-5. A narrowbanded interferometer could detect a known millisecond pulsar with ε as small as 2x10-8(1000Hz/f)2(r/10kpc), where f is the wave frequency (most likely twice the spin frequency) and r is the distance. In an all-sky, all- frequency search the sensitivity would be degraded by a factor of a few to ~15. • Stochastic Waves: The sensitivity improvement of Advanced LIGO, coupled with the decrease in lower frequency cutoff, means that an observational measurement of the

49 LIGO M030023-00M

stochastic gravitational wave background can be performed with a sensitivity after 1 year -9 of observation of ΩGW~5x10 (ΩGW is the ratio of the stochastic gravity-wave energy density contained in a bandwidth ∆f = f to the total energy density required to close the universe; a flat spectrum is assumed).The sources of such background in the LIGO band are all highly speculative and could be weaker than 5x10-9 if they exist at all, but also might be stronger and detectable. Some examples can be given: cosmic strings and other topological defects in the structure of spacetime, first-order phase transitions in the states of quantum fields at temperature ~109 K in the very early universe, Goldstone modes of scalar fields that arise in supersymmetric and string theories, coherent excitations of our 3+1 dimensional universe, regarded as a brane in a higher dimensional universe, and the birth of the universe as described by string-motivated “pre-big-bang” cosmology. • The Unexpected: We are very ignorant of the gravitational universe, and it seems quite probable that Advanced LIGO’s observations will bring some significant surprises.

Vela Spindown Upper Limit Crab Spindown Upper Limit Ω = 1 0 -7

1 -22 0 M

1/2 O 10 o/1 G 0M LI o BH l Ω /BH tia = in i 1 sp In 0 - ir

(f) / Hz a 9 l 1 r c s 0 0M lsa kp pc u 0 1 Me P rge n r= r w , 50M o -6 / B 0 B o 50 H Kn 1 H/ M /B = BH o H I NB Adv LIGO ε

h(f) andh -23 Mer nsp 10 NS ger, ira /N z= l 40 Sco X-1 BH/ S 2 0M B Ins p Me H pir c rge Ins al 3 r pir 00 al, M W z= pc B -7 c 0 ; NS A 0 Ω .4 d 1 kp /B v = 0 = H L ε 1 1 Ins IG 0 -1 pi O r= 1 ra l 65 0M LMXBs pc -24 10 20Mo/20Mo BH/BH Merger, z=1 10 20 50 100 200 500 1000 frequency, Hz

Figure 16 The estimated signal strengths hs(f) from various sources (thin lines, filled circles and star) compared with the noise h(f) (heavy lines) of three interferometers: initial LIGO, Advanced LIGO in a wideband (WB) mode, and Advanced LIGO narrowbanded (NB) at 600 Hz. See text for explanations of sources. The signal strength hs(f) is defined in such a way that, wherever a signal point or curve lies above the interferometer's noise curve, the signal, coming from a random direction on the sky and with a random orientation, is detectable with a false alarm probability of less than one per cent using currently understood data analysis algorithms.

Reference Design Options and Selection

The Advanced LIGO reference design has as its baseline that all three LIGO interferometers will be upgraded as described. It assumes, furthermore, that the upgrades will produce identical interferometers, though they may be run with different detailed parameters such as output laser

50 LIGO M030023-00M power and different signal tuning and signal-recycling mirror transmission. The principal options for the reference design are described below.

Number of Upgraded Interferometers

The upgrade could be restricted to a single interferometer at each LIGO site. The Hanford 2- kilometer interferometer could be retained in its present configuration or decommissioned. However, in the discovery phase of LIGO observations, prior to confirmed observation of gravitational waves, the third interferometer may provide additional confidence and an increase of the volume of the universe that LIGO can see by as much as 50%; in the phase after initial detections, an additional interferometer could be tuned and used in combination with the other LIGO instruments and with other networked detectors to significant astrophysical advantage If the upgrade of the third interferometer is dropped from the scope of the Advanced LIGO project, it will reduce the costs and resources required.

2-Kilometer Interferometer Upgraded but Not Converted to 4 Kilometer Length

This option could be employed if it is felt that a half-size gravitational wave signal is useful in separating genuine signals and that retaining this feature outweighs the advantages of increasing sensitivity that accompanies an increase in arm length. At this time, the improved sensitivity of the longer interferometer is compelling, and we choose to increase the arm cavity length in the reference design. If extending the arm cavity is dropped from the scope of this upgrade, the costs and resources required will be modestly reduced from those required in the baseline design.

Simultaneous Implementation of the Upgrade

Our baseline plan calls for a staged implementation of the upgrade, in which the Livingston instrument installation is started first, with the installation at Hanford to follow by 8 months. This distributes both fabrication and installation demands over a reasonable period. An alternative would be to engage in a simultaneous installation at the two observatories. This would stress the manpower and the facilities, and would require some duplication of installation equipment. It would potentially reduce the duration during which the pair of LIGO observatories are “off-line.” Simultaneous implementation may increase the costs, resources and schedule required to complete the Advanced LIGO upgrade.

Test Mass Substrate Material

Sapphire is selected as the substrate material in this reference design. It offers significant advantages in reducing thermal noise and in control of thermal distortions on the optics. It requires greater development and carries greater risk than fused silica in crystal growth, cost, optical performance, polishing and coating. Our program will carry fused silica as a fallback option, with some impact on the detector sensitivity, with a well-defined date for confirmation of sapphire or adoption of fused silica for the baseline. If sapphire is dropped from the baseline reference design, the costs, schedule and resources required for Advanced LIGO will likely be unchanged.

Future Incremental Upgrades to Advanced LIGO

The Reference Design balances technical challenges and improved performance. The stability of the design through the intensive R&D effort to date has demonstrated its robustness. The design is, however, flexible and can accommodate all foreseeable improvements to this type of detector;

51 LIGO M030023-00M a room-temperature, transmissive-optic, Fabry-Perot Michelson. Some examples that have been explored are as follows:

• Quantum non-demolition techniques: The baseline sensing system experiences the stored light as an “optical spring” which helps to reduce the quantum noise below the naïve limit. Modifications to the interferometer’s input and/or output port fields may allow further reduction of quantum noise. • Newtonian background cancellation: The changes in mass distribution near the test masses (primarily due to seismic noise) appear as a low-frequency noise limit. Monitoring this motion with an array of seismometers may allow a regression or cancellation to observe at lower frequencies. • Non-Gaussian laser light profiles: The thermal motion of the mirror surface, especially for the thermoelastic noise which dominates in the case of sapphire, has a smaller net effect for larger light beams. Introduction of slightly non-spherical end test masses would lead to non Hermite-Gaussian modes with a larger waist that could reduce this noise source, giving better sensitivity at intermediate frequencies. • Variable reflectivity signal recycling mirror: The tunability of the interferometer response is limited with a fixed transmission signal-recycling mirror. Forming a low-finesse output- coupling cavity from a substrate coated on both sides could allow a thermally tuned output coupler, giving a broader range of instrument response functions.

These options may be proposed after observation with the present baseline design for Advanced LIGO. Some may be able to be incorporated into the design shortly after, or coincident with, the commissioning of the baseline. For example, the variable reflectivity signal-recycling mirror has been proposed as an Advanced LIGO contribution from the Australian consortium ACIGA (see next section).

52 LIGO M030023-00M

3. Program Plan

LIGO Laboratory Role and Responsibilities

Scientists, engineers, and staff at the California Institute of Technology (Caltech) and the Massachusetts Institute of Technology (MIT) carry out the design, construction, and operation of the LIGO Observatories. Caltech has prime responsibility for the project under the terms of a Cooperative Agreement39 with the National Science Foundation (NSF). LIGO is a national facility for gravitational-wave research, providing opportunities for the broader scientific community to participate in detector development, observations and data analysis. Under the Cooperative Agreement, the LIGO Laboratory assumes responsibility for implementation of the Advanced LIGO upgrade project.

Figure 17 illustrates the reporting relationship between the LIGO Laboratory and the managing institutions, NSF, Caltech and MIT.

NSF

National Science Board

Director of NSF

Mathematical and Budget and Finances Physical Sciences

Division of Grants Physics and Agreements Cooperative Agreement LIGO Program Management

MIT CALTECH

President President Legal Counsel Memorandum of Understanding Provost

LIGO Dean of Science Oversight Committee Provost VP Business CIT/MIT and Finance Center for Space Physics Mathematics Office of Sponsored Physics Research and Astronomy Research

LIGO Laboratory

MIT LIGO CIT LIGO

Figure 17 LIGO Laboratory Reporting and Oversight

The LIGO Laboratory will manage Advanced LIGO construction in the same manner as the original LIGO construction was executed. A project organization will be established within the LIGO Laboratory with a Work Breakdown Structure (WBS) defining the tasks leading to project deliverables. The project organization will parallel the deliverables in the WBS. Task Leaders for

39 Cooperative Agreement PHY-0107417 between the National Science Foundation, Washington, D.C. 20550 and the California Institute of Technology, Pasadena, CA 91125; LIGO Construction was performed under Cooperative Agreement PHY-9210038.

53 LIGO M030023-00M each organizational element will be charged with delivering the elements of Advanced LIGO. Prior to initiating the Advanced LIGO project, a Advanced LIGO Project Management Plan will define the details of this organization. Advanced LIGO construction will be a broad effort of the LIGO Scientific Collaboration (LSC), and the WBS and organization chart will reflect the collaborative distribution of the responsibilities.

LIGO Scientific Collaboration Role and Responsibilities

Collaborating groups have established the LSC to carry out the LIGO research and development program, to develop priorities, and to enable participation. It is organized as a separate entity distinct from the LIGO Laboratory. Through its Spokesperson, the LSC communicates with the Laboratory through the Laboratory Directorate.

Collaborative work between the LIGO Laboratory and the LIGO Scientific Collaboration is defined in Memoranda of Understanding (MOU)40 between the Laboratory and responsible institutions. Specific tasks are included in Attachments to these MOUs with defined deliverables and periods of performance. A specific MOU and Attachment define membership by an institution in the LSC. Fulfillment of the commitments made by both parties to Attachments is reviewed by periodic progress reports and by revision of the Attachments to define future commitments.

Member institutions in the LSC participate in the research and development program leading to enhanced LIGO detectors. These activities are defined in MOUs and Attachments, and, where applicable, through awards from the NSF.

Participation by member LSC institutions in the execution of the Advanced LIGO construction project is possible and encouraged. Such participation will be governed by specific Attachments defining each institution’s roles and contributions to the Advanced LIGO project. This management technique has been used successfully in the execution of initial LIGO construction. Participant institutions may receive needed funding through subcontracts with the LIGO Laboratory or through funding from other agencies or foreign sources depending upon the particular role and situation of each institution. The NSF is fully involved in reviewing and approving participation by non-NSF supported institutions.

This Project Book represents the definition of the Advanced LIGO project as jointly defined by the LIGO Laboratory and the LSC.

International Collaboration in Advanced LIGO

A major role in Advanced LIGO R&D, construction and implementation is proposed for the GEO Project41, a collaboration of United Kingdom and German institutions. The GEO Project has carried out extensive research and development of technologies fundamental to the Advanced LIGO design. They have designed and are commissioning a 600-meter interferometer that will serve, in addition to its intrinsic goals as a gravitational wave detector, as a test bed for Advanced LIGO techniques. They are carrying out important research in suspension of core optics, in reduction of thermal noise, in relevant materials processing, in modeling of instrument performance and sensitivity, in data acquisition and analysis, and in advanced interferometer configurations. Much of this work is directly relevant to defining the Advanced LIGO detector system.

The GEO institutions will lead the definition, design and construction of the suspensions for the Advanced LIGO test mass optics. Based upon the GEO-600 multiple pendulum suspensions, the Advanced LIGO version makes a pivotal contribution to the performance enhancement of LIGO.

40 http://www.ligo.org/mou/mou.html 41 http://www.geo600.uni-hannover.de/

54 LIGO M030023-00M

Similarly, the GEO work in signal tuned interferometer configurations underpins the Advanced LIGO design and performance goal and GEO is undertaking a continuing role in this area. GEO is assuming responsibility to develop and construct the Advanced LIGO Prestabilized Laser systems. GEO has proposed direct support of the Advanced LIGO project to the United Kingdom funding agencies, and plans a request to the German funding agencies42. The GEO role in executing and participating in the management of the project will be defined through the bilateral MOU and Attachment process described here.

A significant role in Advanced LIGO R&D, construction and implementation is also proposed for the Australian Consortium for Interferometric Gravitational Astronomy43 (ACIGA). ACIGA has an active R&D program on Advanced LIGO techniques including research on the design and development of a 100 W class laser and optical systems compatible with those power levels, control systems for advanced interferometer configurations, and data analysis. ACIGA is constructing a facility at its Gingin site to test the performance of optical systems subjected to high power, a crucial experimental analysis of one of the key Advanced LIGO concepts. Furthermore, ACIGA proposes to expand the capability of Advanced LIGO by leading the development of a variable reflectivity signal recycling mirror, which will allow in-situ manipulation of the instrument’s bandwidth. If this technique is incorporated into the Advanced LIGO baseline, ACIGA will assume responsibility to develop and construct such mirrors for use on at least one of the Advanced LIGO interferometers. ACIGA is proposing direct support of the Advanced LIGO project to the Australian Research Council. It has already been funded for the test facility construction.

Method of Accomplishment

Advanced LIGO is an effort of the entire LIGO Scientific Collaboration. The LIGO Laboratory will manage the project with oversight of all participating institutions. This management will be defined in the MOUs and Attachments for participating institutions outside the LIGO Laboratory. Within the Laboratory, tasks will be assigned to designated Task Leaders and assigned staff reporting to these Task Leaders. Task leaders may come from the greater LIGO Scientific Collaboration, working with a liaison within the Laboratory.

For each component, supply or service required for Advanced LIGO, the Laboratory will employ either an in-house fabrication or provision of the item or service, or will procure the item or service through a subcontract. It is expected that a substantial fraction of the Advanced LIGO system components will be procured through subcontracts based upon the Advanced LIGO project specifications. The Laboratory and scientific partners will primarily carry out design, contractor supervision, receipt, testing, acceptance, final assembly, installation, integration and commissioning. Formal management of subcontracts will in general be the responsibility of the LIGO Laboratory under the terms of the Cooperative Agreement, though international partners will carry out some subcontracting directly.

42 Exploring the Dark Side of the Universe: Proposal for UK Involvement in Advanced LIGO, available at http://www.physics.gla.ac.uk/gwg/AdvLIGO%20Proposal%20Web%20Version.pdf 43 http://www.anu.edu.au/Physics/ACIGA/

55 LIGO M030023-00M

4. Work Breakdown Structure (WBS)

The LIGO Work Breakdown Structure prior to Advanced LIGO construction is:

1.0 Initial LIGO Construction 2.0 LIGO Laboratory Operations 3.0 LIGO Laboratory Advanced R&D

For Advanced LIGO construction, we establish a new top-level WBS designation:

4.0 Advanced LIGO Project

The definitions of the Advanced LIGO first and second level WBS elements are:

4.0. Advanced LIGO Project (Advanced LIGO)

This element includes all costs for removal and securing initial LIGO systems, R&D and design, prototype testing, fabrication of items for the upgrade, and all materials and labor necessary to bring the system to completion of the installation phase. It does not include the labor for the final commissioning or for the operational phase.

4.1. Facility Modifications (FAC)

This element includes modifications and additions to buildings, vacuum systems, and permanent fixed infrastructure that are needed to support the Advanced LIGO detectors. It does not include other facility additions or modifications carried out as normal operations or maintenance tasks.

4.2. Seismic Isolation Subsystem (SEI)

This element includes all R&D, design, prototype testing, and hardware for the seismic isolation system upgrade. It includes all components of active elements including programmable controls items, and software specific to local control of this subsystem. It does not include general controls for the interferometer, nor shared controls infrastructure.

4.3. Suspension Subsystem (SUS)

This element includes all R&D, design, prototype testing, and hardware for the suspension subsystem upgrade, including suspension fibers and attachment to the core optics. It includes the intermediate masses. This element provides small suspensions mechanical hardware for other subsystems. It includes all physical hardware for sensing and control (including the electrostatic actuator, but not the photon actuator) of suspended masses. It includes all components of active elements including programmable controls items, and software specific to local control of this subsystem. It does not include general controls for the interferometer, nor shared controls infrastructure. It does not include controls hardware and software specific to other subsystems for which the mechanical suspensions are supplied by this element.

56 LIGO M030023-00M

4.4 Prestabilized Laser Subsystem (PSL)

This element includes all R&D, design, prototype testing, and hardware for the prestabilized laser subsystem upgrade (one operational and one spare per interferometer, and two prototypes). It includes all components of active elements including programmable controls items, and software specific to local control of this subsystem. It includes the final intensity stabilization system. It does not include general controls for the interferometer, nor shared controls infrastructure.

4.5. Input Optics Subsystem (IO)

This element includes all R&D, design, prototype testing, and hardware for the input optics subsystem upgrade. Suspension mechanical hardware is provided by the suspension subsystem, and controls are provided by the interferometer sensing and controls subsystem. It includes all other components of active elements including programmable controls items, and software specific to local control of this subsystem. It does not include the shared controls infrastructure.

4.6. Core Optics Components (COC)

This element includes all R&D, design, prototype testing, design, purchase of materials, polishing, coating, metrology, cleaning and preparation and transport of the core optics and spares. It includes preparations of the optic for installation in the suspension, but it does not include physical elements attached to the optics required for suspension fiber attachment.

4.7. Auxiliary Optics Subsystem (AOS)

This element includes all R&D, design, prototype testing, and hardware of the output optics subsystem (OO) (all telescopes, output mode cleaner, and miscellaneous steering optics), the stray light control (SLC) subsystem (beam dumps and baffles), the photon actuator for the test mass suspensions (PHO), and the active optics thermal compensation subsystem (AOC). Controls are designed by the interferometer sensing and controls subsystem.

4.8. Interferometer Sensing and Controls Subsystem (ISC)

This element includes all R&D, design, prototype testing, and hardware for the sensing, signal conditioning and digital conversion electronics, programmable items, computers, and software for the servocontrol of the Advanced LIGO interferometer systems. These include control and coordination of all degrees of freedom of the interferometer up to the interface points with the PSL, AOS, SUS, and SEI subsystems, and sensing and readout of lengths and angles of optical elements.

4.9. Data Acquisition, Diagnostics, Network & Supervisory Control (DAQ)

This element includes all R&D, design, prototype testing, and hardware for the analog and digital signal conditioning electronics, computers, programmable items, networking, software, sensors, actuators and excitation devices for reading Advanced LIGO data and diagnostic data and operating diagnostic systems. Common elements of the supervisory control and human interface for subsystems, and the infrastructure (cable plant, servers, etc.) are also in this subsystem. The element includes all additions and modifications to the LIGO Global Diagnostics System (GDS) and the Physics Environmental Monitor (PEM) system.

4.10. Support Equipment (SUP)

This element includes support equipment additions and upgrades needed to install, operate and maintain the Advanced LIGO systems. This element represents equipment, interface systems and support infrastructure that is not subsystem specific.

57 LIGO M030023-00M

4.11. Advanced LIGO Construction Project Research and Development (R&D)

This element includes those R&D activities required to specifically address Advanced LIGO implementation in addition to that planned per subsystem. It is reserved for R&D tasks identified during the fabrication phase and early installation and commissioning. It does not include any tasks included within the LIGO Advanced R&D program currently supported by the NSF and related to Advanced LIGO nor any R&D activities normally carried out within the LIGO Laboratory operations program (WBS 2.0). There are currently no activities in this WBS.

58 LIGO M030023-00M

4.12. Data Analysis and Computing Subsystem (COMP)

This element includes all incremental upgrades to data analysis systems and computational infrastructure needed to support the analysis of data from Advanced LIGO. It includes neither software nor computing nor network hardware supported normally by the LIGO Laboratory operations program (WBS 2.0). It does include the LIGO Data Analysis System (LDAS) and the End-to-End Model (E2E) infrastructure development.

4.13. Installation and Commissioning Task (INS)

This element includes all support for the installation and subsystem commissioning of Advanced LIGO. It also includes all effort to remove and preserve all components of the initial LIGO subsystems not employed in Advanced LIGO.

4.14. Project Management (PM)

This element includes all costs of management of the Advanced LIGO construction incremental to the support provided by the LIGO Operations budget (WBS 2.0). These costs will support cost estimating, scheduling, performance definition and measurement, acquisition, quality assurance, ES&H, document control, review and consultation, and system engineering.

59 LIGO M030023-00M

5. Facility Modifications (FAC)

Overview

Advanced LIGO technical requirements will necessitate modifications and upgrades to the LIGO buildings, and vacuum equipment. In addition, the strategy for executing the Advanced LIGO construction will require some facility accommodations.

The principal impact on this WBS element is as follows:

• It is a program goal to minimize the period during which LIGO is not operating interferometers for science. For this reason, major subsystems such as the seismic isolation and suspension subsystems should be fully assembled and staged in locations on the LIGO sites ready for installation into the vacuum system as fully assembled and vacuum compatible units. This will require prepared assembly and staging space, materials handling equipment, and softwall clean rooms. • Increasing the arm cavity length for the Hanford 2-kilometer interferometer to 4 kilometers will require removing and reinstalling the existing mid-station chambers and replacing them with spool pieces in the original locations. An alternate strategy would be to fabricate additional vacuum tanks for the end stations, and associated spool pieces and preparation. Moving the existing chambers is the choice for the baseline design. • Following the exposure to initial LIGO components and in response to Advanced LIGO requirements it may be necessary to re-bake the vacuum chambers. The reference design does not include a rebake of the major isolatable volumes of the vacuum equipment, but this possibility has been accommodated in our risk analysis and contingency planning No re-baking of the beam tube is needed.

Functional Requirements

Vacuum Equipment

All vacuum equipment functional requirements are the same as those in the initial LIGO design except that the vacuum level must be one order of magnitude lower (<10-7 torr). Additional equipment (chambers, spool pieces, softwall clean rooms) is needed to accommodate additional arm cavity length for one interferometer and the desire for parallel assembly and installation in more chambers and staging areas. A larger diameter spool piece for the IO Mode Cleaner beam path (and possibly for a similar output mode cleaner) is required. The seismic isolation system requirements44 call for the Advanced LIGO subsystems to be compatible with the original LIGO vacuum envelope.

Beam Tube

The original end-pumped beam tube system requires no modifications or additions for Advanced LIGO. There is sufficient margin in the present vacuum performance to permit the operation of the more sensitive Advanced LIGO instrument with no changes.

Conventional Facilities

Preassembly of all large Advanced LIGO seismic isolation units prior to installation in the vacuum tanks requires clean onsite staging and assembly space. At both the Hanford and Livingston

44 LIGO-II Seismic Isolation Design Requirements Document, LIGO-E990303-03-D

60 LIGO M030023-00M

Observatories there exist suitable staging buildings with appropriate height and basic configuration; portable clean rooms and benches are required. Transporters for delivering fragile systems from the central buildings to the end stations are required.

Concept/Options

Vacuum Equipment

Two softwall cleanrooms of the BSC type will be acquired for seismic assembly in the Hanford staging building. Two will be required for Livingston. For each of the interferometers, additional clean rooms will be acquired to support parallel installation in additional chambers to facilitate reducing the duration of Advanced LIGO installation.

Four additional spool pieces will be acquired to replace the Hanford mid-station BSC chambers. The chambers will be removed and reinstalled at the end stations. An alternative approach involves acquiring new BSC chambers and leaving the original chambers in place. Vacuum controls will be added at the end stations to accommodate the BSC chambers in their new location.

The IO (and potentially the output) Mode Cleaner requires a larger diameter spool piece, ~15m in length, to accommodate the larger mirrors used.

The requirement of base pressure for Adv LIGO (<10-7 torr) is already met by the present system (which is operating at <10-8 torr). In the event of long-term contamination or identification of a problematic component, the vacuum equipment isolatable volumes may require baking. We include resources to bake out all isolatable volumes Some schedule impact if this complete bakeout is required.

Beam Tube

No action needed. The original installation meets requirements for Advanced LIGO.

Conventional Facilities

The existing staging buildings at both observatories will require additions of flow benches, hoods, and other minor equipment to support clean processing operations. In addition, at LHO some retrofit of the HVAC system will be necessary in the Staging Building to meet the cleanliness requirements. HEPA filters and a more powerful motor are needed.

R&D Status/Development Issues

There are no development issues or R&D associated with this WBS element.

Work Plan

Long lead procurements dominate this schedule sensitive WBS element. With funding assumed to commence in FY2005, contracts can be placed promptly for the softwall clean rooms and flow benches. These must be in place prior to commencement of seismic assembly by mid 2006. Similarly, procurement of vacuum equipment for conversion of the Hanford 2-kilometer interferometer should commence in 2005.

61 LIGO M030023-00M

6. Seismic Isolation Subsystem (SEI)

Overview

The seismic isolation subsystem serves to attenuate ground motion in the observation band (above 10 Hz) and also to reduce the motion in the “control band” (frequencies less than 10 Hz). It also provides the capability to align and position the load. Significantly improved seismic isolation will be required for Advanced LIGO to realize the benefit from the reduction in thermal noise due to improvements in the suspension system. The isolation system will be completely replaced, and this offers the opportunity to make a coordinated design including both the controls and the isolation aspects of the interferometer.

Functional Requirements

The top-level constraints on the design of the isolation system can be summarized:

• Seismic attenuation - The amplitude of the seismic noise at the test mass must be equal to or less than the thermal noise of the system (10-19 m/√Hz at 10 Hz) for the lowest frequencies where observation is planned. We have chosen 10 Hz as, at this frequency, the competing noise sources (suspension thermal noise, radiation pressure, Newtonian background) all conspire to establish a presently irreducible sensitivity level roughly a factor of 30 above the limits imposed by the LIGO facilities, and because technical difficulties in suspension design make a lower goal unrealistic. • The RMS differential motion of the test masses while the interferometer is locked must be held to a small value (less than 10-14 m) for many reasons: to limit light fluctuations at the antisymmetric port and to limit cross coupling from laser noise sources, as examples. Similarly, the RMS velocity of the test mass must be small enough and the test mass control robust enough that the interferometer can acquire lock This establishes the requirement on the design of the seismic isolation system in the frequency band from 0.1 to 10 Hz. • The isolation positioning system must have a large enough control range to allow the interferometer to remain locked for extended periods; our working value is 1 week. • The system must interface with the rest of the LIGO system, including LIGO vacuum equipment, the adopted suspension design, and system demands on optical layout and control.

A more complete reference on Advanced LIGO seismic isolation requirements is available45.

Concept

The initial LIGO seismic isolation stack will be replaced with an external (to the vacuum) low- frequency pre-isolator stage, and an in-vacuum two-stage active seismic isolation platform (Figure 18 is taken from the design model). The in-vacuum stages are mechanically connected with stiff springs, yielding typical passive resonances in the 2-8 Hz range. Sensing its motion in 6 degrees of freedom and applying forces in feedback loops to reduce the sensed motion attenuates vibration in each of the two-cascaded stages. The outer stage derives its feedback signal by blending three real sensors for each degree of freedom: a long-period broadband seismometer, a short-period geophone, and a relative position sensor. The inertial sensors (seismometers and geophones) measure the platform's motion with respect to their internal suspended test masses. The position sensor measures displacement with respect to the adjacent stage. The resulting “super-sensor” has adequate signal-to-noise and a simple, resonance-free

45 LIGO-II Seismic Isolation Design Requirements Document, LIGO-E990303-03-D

62 LIGO M030023-00M response from DC to several hundred Hz. The inner stage uses the position sensor and high- sensitivity geophone, and some feed-forward from the outer stage seismometer.

Figure 18 Computer rendering of the conceptual design of the two-stage active isolation system for the test-mass (BSC) vacuum chambers. The outside frame supports the first stage from three trapezoidal blade springs. Three plug-in units carry the sensors and actuators for the unit. The inner second stage is likewise suspended from trapezoidal springs, with the sensor/actuators protruding above the upper surface. The optics are suspended below the inner stage (which forms the interface to the suspension and other isolated parts), and hang below the support structure (HPD).

The outer frame of the isolation system is designed to interface to the existing in-vacuum seismic isolation support system, simplifying the effort required to exchange the present system for the new system. The outer stage is hung from the outer frame using trapezoidal leaf springs to obtain the 2-6 Hz resonances. The inner platform stage is built around a 1.5-m diameter optics table (BSC) or a larger polygonal table (HAM). The mechanical structures are carefully studied to bring the first flexible-body modes well above the ~50 Hz unity gain frequencies of the servo systems. For each suspended optic, the suspension and auxiliary optics (baffles, relay mirrors, etc.) are mounted on an optical table with a regular bolthole pattern for flexibility.

We will use commercial, off-the-shelf seismometers that are encapsulated in a removable pod. This allows the sensors to be used as delivered, without concerns for vacuum contamination, and allows a simple exchange if difficulties arise. The actuators consist of permanent magnets and coils in a configuration that encloses the flux to reduce stray fields. These components must meet the stringent LIGO contamination requirements. The multiple-input multiple-output servo control system is realized using digital techniques; 16-bit accuracy with ~2 kHz digitization is sufficient.

63 LIGO M030023-00M

The external pre-isolator is used to position the in-vacuum assembly, with a dynamic range of 1 mm, and with a bandwidth of 2 Hz or greater in all six degrees of freedom. This allows feedforward correction of low-frequency ground noise and sufficient dynamic range for Earth tides and thermal or seasonal drifts. We target approximately a factor of 10 reduction of the ~0.16 Hz microseismic motion from feedforward correction in this stage. For corrections up to the 1-cm clearance at each vacuum feedthrough bellows, large screw adjustments are included in series with each external actuator.

The performance of the system, and its initial design, is calculated with a model that includes all solid-body degrees of freedom, and measured or published sensitivity curves (noise and bandwidth) for sensors. It meets the Advanced LIGO requirements with some margin, for both the test-mass (BSC) and auxiliary (HAM) chambers.

The passive isolation of the suspension system provides the final filtering. A sketch of the system as applied to the test-mass vacuum chambers (BSC) is shown in Figure 19; a similar system is designed for the auxiliary optics chambers (HAM). Further details can be found in the subsystem Design Requirements and Conceptual Design documents46.

Figure 19 Rendering of isolation system installed in the BSC (Test Mass Chambers), with suspension system attached below .The external preisolator provides the interface between the vertical blue piers and the green horizontal support structure (C. Hardham, Stanford).

46 Advanced LIGO Seismic Isolation System Conceptual Design, E010016-00

64 LIGO M030023-00M

R&D Status/Development Issues

A first-generation prototype47 of the in-vacuum isolation system has shown performance at low- and high-frequencies comparable to the requirements. Testing of a preliminary version of the external pre-isolator48 is nearing completion and will be installed in Livingston in 2003 as a remedial effort addressing excess local seismic noise. Testing started in December 2002 on a second-generation prototype of the in-vacuum isolation at the Stanford Engineering Test Facility49.

Several issues must be addressed. The most significant is identifying the character of the internal mechanical resonances of as-built designs and crafting control laws that meet requirements in this environment. Other issues include minimizing the confusion of tilt with horizontal motion for low-frequency control, the distribution of control authority through the hierarchy, and stability of parameters (for feed-forward and loop gain design). In addition, processors, analog interfaces, and software systems that are compatible with the LIGO standard will be integrated into the subsystem.

Materials issues requiring study include the development of contamination-compatible in-vacuum electromagnetic actuators, and creep and yield behavior of structural materials under stress.

Work Plan

The present LIGO Cooperative Agreement and existing NSF grants to LSC member institutions will support research, development, and design on this subsystem through full-scale tests carried out in the MIT LASTI testbed. These involve control and noise-performance tests of complete systems for both the test-mass and the auxiliary optics vacuum chambers, as well as their integration with the suspensions (SUS).

Advanced LIGO construction will commence with a final design review and with placement of production subcontracts for all seismic subsystem components. Fabricated components must begin arriving at the staging buildings at the two sites in early 2006.

Assembly of complete seismic system units in the staging buildings will take place during 2006. Sufficient systems must be completed at both sites to support installation in the interferometer vacuum chambers in mid-2006.

47 R. Abbott, R. Adhikari, G. Allen, S. Cowley, E. Daw, D. DeBra, J. Giaime, G. Hammond, M. Hammond, C. Hardham, J. How, W. Hua, W. Johnson, B. Lantz, K. Mason, R. Mittleman, J. Nichol, S. Richman, J. Rollins, D. Shoemaker, G. Stapfer, and R. Stebbins. Seismic isolation for advanced LIGO. Classical and Quantum Gravity 19(7):1591, 2002. P010027-01-R 48 Initial LIGO Seismic Isolation Upgrade Design Requirements Document, T020033-02-D 49 http://www.ligo.caltech.edu/docs/G/G010193-00.pdf

65 LIGO M030023-00M

7. Suspension Subsystem (SUS)

Overview

The test-mass suspension subsystem must preserve the low intrinsic mechanical losses (and thus the low thermal noise) in the fused silica suspension fibers and sapphire test mass material. It must provide actuators for length and angular alignment, and attenuate seismic noise. The Advanced LIGO reference design suspension is similar in design to the GEO 600 multiple pendulum suspensions, with requirements to achieve a seismic wall of ~10 Hz. A variety of suspension designs are needed for the main interferometer and input conditioning optics.

Functional Requirements

The suspension forms the interface between the seismic isolation and the suspended optics. It provides seismic isolation and the means to control the orientation and position of the optic. These functions are served while minimally compromising the thermal noise contribution from the test mass mirrors and only introducing a negligible amount of thermal noise from the suspension elements.

The optic (which in the case of the main arm cavity mirror serves also as the test mass) is attached to the suspension fiber during the suspension assembly process and becomes part of the suspension assembly. Features on the test mass will be required for attachment and potentially for actuation. The test mass suspension system is mounted (via bolts and/or clamps) to the seismic isolation system by attachment to the SEI optics table.

Local signals are generated and fed to actuators to damp solid body motions of the suspension components; in addition, control signals generated by the interferometer sensing/control (ISC) are received and turned into forces on the test mass to obtain and maintain the operational lengths and angular orientation. There are two variants of the test mass suspension: one for the End Test Mass (ETM) which carries potentially non-transmissive actuators behind the optic, and one for the Input Test Mass (ITM) which must leave the input beam free to couple into the Fabry-Perot arm cavity. There are also variants for the beamsplitter, folding mirror, and recycling mirrors; and for the mode cleaner, input matching telescope, and suspended steering mirrors.

A multiple-pendulum is the basis. This has two benefits:

• it provides a mechanical filter to reduce noise injected by the controllers and the thermal noise of the lower Q isolation stages above, • it enables a considerable reduction of control forces exerted on the test mass itself.

The latter feature will allow the elimination of the magnets attached to the test mass in initial LIGO (which are the largest source of excess dissipation on the test mass), and should allow the test mass to reach a mechanical loss (and thus thermal noise) limited principally by the substrate material. Furthermore, eliminating the magnets reduces a potential source of correlation between the interferometers due to correlated environmental magnetic fields. Thus both technical noise and fundamental thermal noise should be substantially reduced in such a suspension.

Multiple simple pendulum stages also improve the seismic isolation of the test mass for horizontal excitation of the pendulum support point; this is a valuable feature, but requires augmentation with vertical isolation to be effective. Vertical seismic noise can enter into the noise budget through a variety of cross-coupling mechanisms, most directly due to the curvature of the earth over the baseline of the interferometer. Simple pendulums have high natural frequencies for vertical motion. Thus, another key feature of the suspension is the presence of additional vertical

66 LIGO M030023-00M compliance in the upper stages of the suspension to provide lower natural frequencies and consequently better isolation.

Further detail can be found in the Design Requirements Document.50

Key parameters of the test-mass suspension design are listed in Table 2; other suspensions have requirements relaxed from these values.

Table 2 Test-mass suspension parameters

Suspension Parameter Value Test mass 40 kg, sapphire Penultimate masses fused silica, high-density glass, or low-grade sapphire Upper masses 36 kg, stainless steel Test mass suspension fiber Fused silica ribbon or tapered fiber Upper mass suspension fibers Steel Approximate suspension lengths 0.5 m test mass, 0.3, 0.3 m intermediate, 0.6 m top Vertical compliance Trapezoidal cantilever springs Optic-axis transmission at 10 Hz 10-6 Test mass actuation Electrostatic (acquisition), photon pressure (operation) Upper stage actuation; sensing Magnets/coils; incoherent occultation sensors

50 Test Mass Suspension Subsystem Design Requirements Document, T010007-00-R

67 LIGO M030023-00M

Concept/Options

The testmass mirror is suspended as the lowest mass of a quadruple pendulum as shown in Figure 20; the four stages are in series. Sapphire is the reference design mirror substrate material. However, the basic suspension design is compatible with fused silica masses and a “fall-back” to this alternate may be made shortly before final design. Both materials are amenable to low-loss bonding of the fiber to the test mass. The mass above the mirror -- the intermediate mass -- is made of a moderately low-mechanical-loss glassy or crystalline material such as fused silica, high-density glass, or low-grade sapphire.

The masses at the top are suspended from two cantilever-mounted, approximately trapezoidal, pre-curved, blade springs (inspired by and similar to the VIRGO blade springs), and two steel wires. The blade springs are stressed to about half of the elastic limit.

The penultimate mass is suspended from 4 cantilever springs and 2 steel wire loops. Fused silica pieces form the break-off points at the intermediate mass. These are attached to the penultimate and final mass using hydroxy catalysis bonding, which is demonstrated to contribute negligible mechanical loss to the system. The upper support stages suspension wires are not vertical and this gives some control over mode frequencies and coupling factors.

Tolerable noise levels at the intermediate mass are within the range of experience on prototype interferometers (10-17 m/√Hz) and many aspects of the technology have been tested. There are, however, no meaningful test results at less than ~ 150 Hz. At the top-mass, the main concern is to avoid acoustic emission or creep (vibration due to slipping or deforming parts).

Sensing (for damping) of the solid-body modes of the suspension requires an improved local sensor (required performance ~10-12 m/√Hz at 10 Hz) or an alternative servo configuration to meet the subsystem noise performance requirements.

Actuation is applied to all masses in a hierarchy of lower force and higher frequency as the test mass is approached. Coils and magnets are used on upper stages, with electrostatics (for locking) and photon pressure (for operation) used on the test mass itself.

Other suspended optics will have noise requirements that are less demanding than those for the test masses, but still stricter than the initial LIGO requirements, especially in the 10-50 Hz range. Their suspensions will employ simpler suspensions than those for the test masses, such as the triple suspension design for the mode cleaner mirrors shown in Figure 20.

More design detail can be found in additional subsystem documentation51.

51 Advanced LIGO Suspension System Conceptual Design, T010103-01; N. A. Robertson, G. Cagnoli, D. R. M. Crooks, E. Elliffe, J. Faller, P. Fritschel, S. Gossler, A. Grant, A. Heptonstall, J. Hough, H. L\"uck, R. Mittleman, M. Perreur-Lloyd, M. V. Plissi, S. Rowan, D. H. Shoemaker, P. Sneddon, K. A. Strain, C. I. Torrie, H. Ward, P. Willems: Quadruple Suspension Design for Advanced LIGO, Class. Quantum Grav. Vol. 19 (2002) 4043-4058; P020001-A-R

68 LIGO M030023-00M

Figure 20 Test mass suspension design elevation view sketches.

Figure 21 Test mass suspension rendering

69 LIGO M030023-00M

R&D Status/Development Issues

The primary role of the suspension is to realize the potential for low thermal noise, and much of the research into suspension development explores the understanding of the materials and defines processes to realize this mission. In addition, design efforts ensure that the seismic attenuation and the control properties of the suspension are optimized, and prototyping efforts ensure that the real performance is understood.

The GEO-600 suspensions utilizing the basic multiple-pendulum construction, fused-silica fibers, and hydroxy-catalysis attachments, have been in service since 2001. The systems have been reliable and the controls function as modeled. The noise performance will be demonstrated in 2003.

Significant design and modeling of the mode-cleaner triple suspensions has taken place, and successful careful comparison of the quadruple test-mass model with the MIT/GEO prototype has been made.

Test mass thermal noise is one of the basic noise limits to performance of the Advanced LIGO design. To realize the reference design performance, the following lines of research are being pursued:

• Measurement of the dissipation levels (that determine the levels of thermal noise, according to the Fluctuation-Dissipation Theorem) of the various fused silica and sapphire components and assembled systems, to guarantee that we can reach the levels limited by the best material properties. • Qualification of production techniques to ensure that assembled suspensions meet all of the specifications, including those related to thermal noise. A separate measurement of the Q of components does not guarantee that the complete system will realize its potential. • Verification that we do indeed achieve the expected thermal noise levels, without significant amounts of excess noise; both stationary (best characterized in the frequency domain) and non-stationary (studied in the time domain) performance are issues.

Development of the Advanced LIGO version of the suspension starts with the multiple pendulum scheme based on the GEO 600 suspension, and GEO is leading the trade studies. Within that framework, there are a number of specific questions to address, including:

• choice of masses and dimensions for the masses for each stage, • choice of wires or ribbons, dimensions, means of fabrication, and attachment, • necessity of reaction masses, and designs of this system where required, • sensing and actuation systems for the damping control • establishment of the actuator hierarchy, including whether we can construct a system without any direct actuation on the test mass, and development of electrostatic actuators

Tests for attenuation, parasitic resonances, and other defects in isolation properties (along with consequent modifications of these pendulums) are a focus of the development effort. GEO will characterize their system with Advanced LIGO requirements in mind. Full-scale controls and noise test prototypes are in development and will be used to test performance against requirements in laboratory-scale experiments.

70 LIGO M030023-00M

Work Plan

The R&D program will include work on this subsystem through full-scale tests of all principal variants of the suspensions in the MIT LASTI testbed. By the completion of that test, the design will have been carried through the design requirements, preliminary design, and substantially through the final design review. A final LASTI test will serve to verify form, fit and conformance to functional requirements. Advanced LIGO construction will commence with the final design review and with placement of production subcontracts for all suspension subsystem components. Fabricated components must begin arriving at the optics/vacuum preparation facilities at the two sites in early 2007.

A consortium of the University of Glasgow, University of Birmingham, and Rutherford Appleton Laboratory has proposed to UK funding sources (PPARC) to supply the test-mass suspensions for Advanced LIGO42. The GEO group at the University of Glasgow is the originator of the design, and is very well positioned to carry through with this effort.

Assembly of complete suspension subsystem units in the site facilities will start in 2006. Suspension of the optics in the completed suspension units will be done at the time of final installation. This will require readiness of optics processing and suspension fiber processing systems at each site. Sufficient systems must be completed at both sites to support installation in the interferometer vacuum chambers early in 2007.

71 LIGO M030023-00M

8. Prestabilized Laser Subsystem (PSL)

Overview

The Advanced LIGO PSL will be a conceptual extension of the initial LIGO subsystem, operating at the higher power level necessary to meet the required Advanced LIGO shot noise limited sensitivity. It will incorporate a frequency and amplitude stabilized 180 W laser. The Advanced R&D program related to this subsystem will develop diode laser pumped slab or rod optical gain stages that can be used either in injection locked power oscillators or as a multipass power amplifier.

Functional Requirements

The main requirements of the PSL subsystem are output power, and amplitude and frequency stability. Table 3 lists the reference values of these requirements. Changes in the readout system allow some requirements to be less stringent with respect to initial LIGO; the extension to lower frequency provides the principal challenge.

Table 3 PSL Requirements

Requirement Value

TEM00 Power 180 W

Non-TEM00 Power <5 W Frequency Noise 10 Hz/Hz1/2 (10 Hz) Amplitude Noise 2×10-9 /Hz1/2 (10 Hz) Beam Jitter 2×10-6 rad/Hz1/2 (100 Hz) RF Intensity Noise 0.5 dB Above Shot Noise at 25 MHz for 150 mW

TEM00 Power: Assuming an optical throughput of 0.67 for the input optics subsystem, the requirement of 120 W at the interferometer input gives a requirement of 180 W PSL output. Non-TEM00 Power: Modal contamination of the PSL output light will mimic shot noise at the mode cleaner cavity, producing excess frequency noise. A level of 5 W non-TEM00 power is consistent with the input optics frequency-noise requirements. Frequency Noise: Frequency noise couples to an arm cavity reflectivity mismatch to produce strain noise at the interferometer signal port. The requirement is obtained based on a model with an additional factor of 105 frequency noise suppression from mode cleaner and interferometer feedback, a 0.5% match in amplitude reflectivity between the arm cavities (a conservative estimate for the initial LIGO optics), and a signal recycling mirror of 10% transmissivity. Amplitude Noise: Laser amplitude noise will cause strain noise in two main ways. The first is through coupling to a differential cavity length offset. The second and larger coupling is through unequal radiation pressure noise in the arm cavities. Assuming a beamsplitter of reflectivity 50±1%, the requirement is established. Beam Jitter Noise: The coupling of beam jitter noise to the strain output is through the interferometer optics misalignment. Based on a model of a jitter attenuation factor of 1000 from the mode cleaner, a nominal optic alignment error of 10-9 rad rms imposes the requirement on higher order mode amplitude. RF Intensity Noise: The presence of intensity noise at the RF modulation frequency directly produces strain noise. The noise is limited with the requirement above.

72 LIGO M030023-00M

Concept/Options

The conceptual design of the Advanced LIGO PSL is similar to that developed for initial LIGO. It will involve the frequency stabilization of a commercially engineered laser with respect to a reference cavity. It will include actuation paths for coupling to interferometer control signals to further stabilize the beam in frequency and in intensity. Three options for the laser design are under study: a slab injection-locked stable-unstable resonator, a rod injection-locked stable resonator, and a multipass power amplifier. The technology will be selected in early 2003. The control system of the Advanced LIGO PSL, including amplitude and frequency servos, will be largely adapted and extended from the initial LIGO design.

R&D Status/Development Issues

Three approaches to the development of the laser are being pursued. The target for the power from the laser head is 180 W to accommodate some losses to spatial mismatch from the source laser to the desired TEM00 mode. Sketches of the proposed solutions are shown in Figure 22.

QR output f f pump BP f f

QR HR@1064 YAG / Nd:YAG / YAG HT@808 3x 7x40x7

Figure 22 Three approaches to the high-power laser head. At left, an injection-locked stable-unstable resonator (Adelaide); middle, and end-pumped zig-zag amplifier (Stanford); at right, an injection-locked end-pumped rod system (LZH).

In one approach, the Adelaide University group is prototyping a system in which a low-noise, low power master oscillator injection locks a high power stage, formed with a diode-pumped slab crystal situated in a stable-unstable resonator.

An approach, undertaken by Stanford University, uses the master oscillator-power amplifier (MOPA) configuration. In this approach, the output of a master oscillator is passed one or more times through a series of gain elements. This is the laser configuration in use for the initial LIGO, developed by Lightwave Electronics Corporation based upon earlier Stanford work, which provides 10 W output power. The Stanford group is extending the MOPA design to 180W-output power by using the 10-W laser as a master oscillator and employing additional amplifier stages.

The third approach, pursued at the Max Planck Institute for Gravitational Wave Research/University of Hannover and the Laser Zentrum Hannover, is an end-pumped rod resonator that is injection locked to a master oscillator. It is based on experience with the GEO- 600 laser, but taking the approach from ~25 W to ~200 W.

The overall goal of this advanced R&D effort is to develop the power laser technology to the point where industrial participation in engineering a reliable unit can begin. The Max Planck group will propose to German funding agencies to supply the laser system for Advanced LIGO, and is leading the downselect and conceptual design effort.

73 LIGO M030023-00M

Work Plan

The parallel approach to the development of high power lasers is proceeding, with all three groups approaching the intermediate goal of a 100 W laser. Comparative tests of the three laser designs, with participation from LIGO, are planned for early 2003. After the selection is made, an effort with industry, similar to our practice in initial LIGO, will be undertaken to engineer a reliable unit that will meet the LIGO availability goal. Tests of a complete full-power PSL will be made in the LASTI installation in late 2005. The PSL subsystem design work will proceed in parallel with the laser fabrication, so that the complete subsystem will be ready for installation in early 2007.

74 LIGO M030023-00M

9. Input Optics Subsystem (IO)

Overview

The Advanced initial LIGO subsystem will be an extension of the initial LIGO Input Optics design to the higher specified power and lower noise level of Advanced LIGO. The IO will consist primarily of beam conditioning optics including Faraday Isolators and phase modulators, a triangular input mode cleaner, and an interferometer mode-matching telescope.

Functional Requirements

The functions of the IO subsystem are to provide the necessary phase modulation of the input light, to spatially and temporally filter the light on transmission through the mode cleaner, to provide optical isolation as well as distribution of interferometer diagnostic signals, and to mode match the light to the interferometer with a beam-expanding telescope. Table 4 lists the requirements on the output light of the IO II subsystem.

Table 4 Advanced initial LIGO requirements

Requirement Value

Optical Throughput 0.67 (net input to TEM00 out)

Non-TEM00 Power <5% Frequency Noise 3×10-3 Hz/ Hz1/2 (10 Hz) Beam Jitter 1×10-9 rad RMS

The Input Optics has to deliver 120 W of conditioned power to the advanced LIGO interferometer. The optical throughput requirement ensures that the required TEM00 power will be delivered. The cavities of the main interferometer will accept only TEM00 light, so the IO must remove the higher- order modes and its beam-expanding telescope must couple 95% of the light into the interferometer.

The IO reduces the frequency, and beam-jitter noise of the laser. The suspended mode cleaner serves as an intermediate frequency reference between the PSL and interferometer. Beam jitter (pointing fluctuation) appears as noise at the interferometer output signal through optical misalignments and imperfections. The nominal optic alignment error of 1×10-9 rad imposes the requirement in Table 4. Further details can be found in the IO Design Requirements document52.

Concept/Options

The schematic layout of the IO is displayed in Figure 23, showing the major functional components. The development of the IO for Advanced LIGO will require a number of incremental improvements and modifications to the initial LIGO design. Among these are the needs for larger mode cleaner optics and suspensions to meet the Advanced LIGO frequency noise requirement, and increased power handling capability of the Faraday Isolator and phase modulators.

52 Advanced LIGO Input Optics Design Requirements Document, T020020-00

75 LIGO M030023-00M

Figure 23 Schematic diagram of the Advanced LIGO Input Optics (IO) subsystem.

Phase modulation for use in the length and angle sensing systems is applied using electro-optic crystals. Faraday isolators are used to prevent parasitic optical interference paths to the laser and to obtain information for the sensing system.

The mode cleaner is an in-vacuum suspended triangular optical cavity. It filters the laser beam by suppressing directional and geometric fluctuations in the light entering the interferometer, and it provides frequency stabilization both passively above its pole frequency and actively through feedback to the PSL. Noise sources considered in design studies include sensor/actuator and electronic noise, thermal, photothermal and Brownian motion in the mode cleaner mirrors, and radiation pressure noise. The mode cleaner will use 15-cm diameter, 7.5-cm thick fused silica mirrors. The cavity will be 17 m in length, with a finesse of 2000, maintaining a stored power of ~100 kW. A triple pendulum (part of the suspensions subsystem) will suspend the mode cleaner mirrors so that seismic and sensor/actuator noise does not compromise the required frequency stability.

Finally, the mode-matching telescope, which brings the beam to the final Gaussian beam parameters necessary for interferometer resonance, will be similar to the initial LIGO design, but will use two (rather than three) reflective spherical mirrors. The third element will consist of an adaptive optical lens that will allow for in situ adjustment of mode matching without the need for vacuum excursions. This design allows for optimization of mode-matched power by having independent adjustment of two degrees of freedom, waist size and position, over a wide range of modal space.

Further documentation of the design can be found in the Input Optics Conceptual Design Document53.

53 Advanced LIGO Input Optics Subsystem Conceptual Design Document, T020027-00

76 LIGO M030023-00M

R&D Status/Development Issues

The IO subsystem has completed its Design Requirements and Concept Review and is now in preliminary design. Development of the IO focuses on the need for power handling at the 180 W level and the corresponding development of the Faraday Isolators and phase modulators. For the Faraday Isolator, both wavefront distortion and depolarization effects need to be addressed. A new design54 providing compensation for polarization distortion has shown good isolation up to the maximum test power of 85W. For modulators, we are studying 5 different materials: potassium titanyl phosphate (KTP), potassium titanyl arsenate (KTA), rubidium titanyl arsenate (RTA), rubidium titanyl phosphate (RTP), and lithium niobate (LiNb03). Initial testing suggests that several of these are good candidates, potentially using a compensation approach similar to that for the Faraday Isolator.

Work Plan

Development of high power Faraday Isolators and phase modulators is proceeding under the University of Florida Advanced R&D program, and the subsystem lead role will remain with the University of Florida as for initial LIGO. A complete end-to-end test of the IO will be performed at the LASTI facility in conjunction with the mode cleaner suspension testing and the pre-stabilized laser testing in 2005. Installation will commence in 2007.

54 E. Khazanov, N. Andreev, A. Babin, A. Kiselev, O. Palashov, and D. H. Reitze, “Suppression of Self-Induced Depolarization of High-Power Laser Radiation in Glass-Based Faraday Isolators”, J. Opt. Soc. Am B. 17, 99-102 (2000)

77 LIGO M030023-00M

10. Core Optics Components (COC)

Overview

The Advanced LIGO COC will involve a significant change from the initial LIGO COC to meet the higher power levels and improved shot-noise and thermal-noise limited sensitivity required of the Advanced LIGO interferometer. Many of the fabrication techniques developed for the fused silica initial LIGO COC will be directly applicable to the optics production. However, sapphire is adopted as the baseline substrate material for the test masses in Advanced LIGO. Sapphire is chosen because of its higher mechanical Q, speed of sound, and density, all of which contribute to a significant reduction in the internal thermal noise leading to an improvement of the detector sensitivity by a factor of 2 over fursed silica at 100 Hz, and more at higher frequencies. The larger mass is needed to keep the radiation reaction noise to a level comparable to the suspension thermal noise. Its higher thermal conductivity reduces the thermal lensing due to absorbed laser power. Sapphire does have a greater thermal expansivity, leading to a thermoelastic noise contribution. An R&D effort is underway to develop sapphire in a quality and size appropriate to serve as test mass material. The optical coatings must also undergo development to achieve the combination of low mechanical loss (for thermal noise) while maintaining low optical loss.

Functional Requirements

The COC subsystem consists of the following optics: power recycling mirror, signal recycling mirror, beam splitter, folding mirror, input test mass, and end test mass (see Figure 14). The following general requirements are placed on the optics:

• the radius of curvature and surface figure must maintain the TEM00 spatial mode of the input light; • the optics microroughness must be low enough to limit scatter to acceptable levels; • the substrate and coating optical absorption must be low enough to limit the effects of thermal distortion on the interferometer performance; • the optical homogeneity of the transmitting optics must be high enough to preserve the shape of the wavefront incident on the optic; • the intrinsic mechanical losses, and the optical coating mechanical losses, must be low enough to deliver the required thermal noise performance

Table 5 lists the COC test mass requirements for both fused silica and sapphire materials under consideration for the different types of optics.

Table 5 COC test mass requirements

Sapphire Silica Surface figure 1 nm RMS (deviation from sphere over central 12 cm) Micro-roughness 0.1 nm RMS Optical homogeneity 20 nm pk-pk, double pass (in transmission through 15 cm thick substrate, over central 8 cm) Optical absorption <20 ppm/cm <0.5 ppm/cm Substrate mechanical Q 2×108 3×107 Optical coating optical loss 0.5 ppm/bounce

78 LIGO M030023-00M

Optical coating mechanical loss 2×10-5 (goal)

As the table shows, the figure, roughness and homogeneity requirements are the same for both materials. The absorption requirement is reduced for sapphire because its relatively higher thermal conductivity reduces thermal distortion for a given heat input.

Concept/Options

Sapphire is the reference design for the input and end test mass material because of its promise of reduced internal thermal noise and due to better thermal distortion properties. Internal thermal noise is a limit to interferometer sensitivity at the noise minimum near 100 Hz. As insurance against the risks involved in the sapphire development effort, the option of using ultralow optical absorption fused silica for the test masses is being preserved. The final decision to retain sapphire as the critical test mass material is scheduled before production fabrication must begin. Fabrication of fused silica to meet most of the requirements in the above table has already been demonstrated and is not expected to involve research and development; work would be required to ensure acceptable mechanical losses of fused silica in large substrates, although very low losses have been seen in smaller samples. The material properties of fused silica would require significantly more reliance on the thermal compensation system (see 11. Auxiliary Optics Subsystem (AOS)).

The beam splitter requirements are met by the best presently available low absorption fused silica and the power and signal recycling mirrors of LIGO-I class fused silica. These mirrors do not have the same noise or power handling requirements as the test masses, so fused silica, being more readily available, is chosen.

The very long lead time for production of substrates, for polishing, and for coating (for either substrate choice) makes this the critical path item in the Advanced LIGO schedule. Early funding for purchase of the substrates is needed to maintaining the present planned schedule. R&D Status/Development Issues

Sapphire research and development is well underway. In partnership with industry we are developing the techniques to grow, polish and coat sapphire to the Advanced LIGO requirements; full size boules (which can be tailored to the 32cm diameter testmass size) of sapphire have been produced and are now undergoing an initial polishing phase to allow characterization of the absorption, birefringence and optical homogeneity, demonstrating suitability for the Advanced LIGO test masses. This R&D resembles that employed in initial LIGO, in which a pathfinder process demonstrated that fused silica optics could be brought to the initial LIGO specifications.

Sapphire is a very hard material that requires special polishing. It must be polished to give a smooth surface both on small scales (microroughness), and large scales (surface figure). Samples have been polished to our requirements. In addition, compensation may be needed for the optical inhomogeneities experienced by the wavefront as it is transmitted through the non- uniform optic. Four approaches to optical compensation have been explored; at CSIRO there has been work on ion milling, fluid jet polishing and corrective coating, at Goodrich (see Figure 24) compensation has already been demonstrated on a 250 mm optic using computer controlled corrective polishing. Though ion milling is attractive we have chosen corrective polishing as our baseline since the infrastructure for handling large pieces already exists.

79 LIGO M030023-00M

Figure 24 Sapphire piece used in the spot-polishing compensation demonstration; 25cm diameter sample (photo courtesy Goodrich).

Sapphire substrate optical absorption also is receiving attention. Present measurements of a large set of sapphire test pieces indicate baseline absorption of 50-80 ppm/cm. The R&D effort is aimed at reducing this absorption to 20 ppm/cm. Investigations are underway examining the effect of the purity and preparation of raw material, segregation of impurities during growth, and effects of annealing temperature, duration and atmosphere. These studies have suggested that a simple selection of the best material will not be sufficient and that it will be necessary to do post growth processing, possibly including sample harvesting, regrowth and high temperature purification. Preliminary results, at the time of writing this proposal, indicate that such processing can yield absorption of 50 ppm/cm with regions of 20 ppm/cm. With the use of thermal compensation (see next section), 50 ppm/cm would be acceptable, but 20 ppm/cm gives desirable margin in the design. We will continue to pursue this through the development stage (through early 2004).

A very active program to characterize and reduce the mechanical loss in the coatings has made progress. The principal source of loss in conventional optical coatings has been determined by our research to be associated with the tantalum pentoxide, either due to material losses or due to stresses induced during the coating process. Several alternative materials and processes are being explored with multiple vendors. We have a goal of an approximate factor of ten reduction in the loss, as a coating mechanical loss at this level ensures the coating thermal noise does not significantly reduce the sensitivity of the instrument. We have seen reductions of 2.5 in selected samples of exploratory coatings.

80 LIGO M030023-00M

Work Plan

The sapphire R&D effort will culminate in early 2003, when a decision will be made on whether to proceed with production of sapphire test masses, or instead rely on the fallback plan of ultralow absorption fused silica. Following this selection, fabrication will proceed with the plan for first articles to be available in 2006.

The time scale for developing a satisfactory coating, with appropriate optical and mechanical losses, is associated with the commencement of coatings on the production optics at the end of 2005.

81 LIGO M030023-00M

11. Auxiliary Optics Subsystem (AOS)

Overview

The AOS for Advanced LIGO is an extension of this subsystem for initial LIGO, and will accommodate the planned higher laser power and additional signal-recycling mirror. The AOS is responsible for transport of interferometer output beams and for stray light control. It includes beam reducing telescopes, and beam dumps and baffles. An additional element of this subsystem is active optics thermal compensation, where compensatory heating of an optic is used to cancel thermal distortion induced by absorbed laser power. It also includes the photon actuator, which uses light pressure to adjust the length of the interferometer arms. AOS also covers the addition of an output mode cleaner.

Functional Requirements

The conventional subsystem requirements relate to control of interferometer ghost beams and scattered light, delivery of interferometer pickoff beams to the ISC subsystem, and maintenance of the surface figure of the core optics through active thermal compensation. While the requirements on these elements are somewhat more stringent than for the initial LIGO design, no significant research and development program is required to meet those requirements. Working values for these aspects of the AOS system are shown in

Table 6.

There are elements which are new to the Advanced LIGO design for which the requirements will be numerically determined as part of the systems flowdown:

• Active Thermal Distortion Compensation: The axisymmetric thermal lens must be corrected sufficiently to allow the interferometer to “cold start”; the compensation may also be required to correct for small (cm-) scale spatial variations in the substrate absorption. • Photon Actuator: Forces must be applied to the test mass during the operation of the interferometer to maintain the operating length without compromising the mechanical losses of the system. The photon actuator must have sufficient authority to perform the actuation, without adding noise above a negligible level. • Output Mode Cleaner: The length sensing system requires that non-TEM00 light power at the antisymmetric output port be reduced substantially to allow a small local-oscillator level to be optimal and thus to maintain the efficiency of the overall shot-noise-limited sensing.

Table 6 Auxiliary Optics Subsystem Requirements

Maximum power of undumped ghost Maximum allowed distortion of beams pickoff beams 50 µwatt 1/8 wave

Concept/Options

The AOS conventional elements consist of low-aberration reflective telescopes that are placed in the vacuum system to reduce and relay the output interferometer beams out to the detectors, and baffles of absorptive black glass placed to catch stray and “ghost” beams in the vacuum system. The elements must be contamination free and not introduce problematic mechanical resonances. Because of the increased interferometer stored power, the AOS for Advanced LIGO will involve

82 LIGO M030023-00M careful attention to control of scattered light, and will require greater baffling and more beam dumps than for initial LIGO.

The thermal compensation approach involves adding heat, which is complementary to that deposited by the laser beam, using two complementary techniques: a ring heater that deals with circularly symmetric distortions, and a directed laser that allows uneven absorption to be corrected.

The frequency-dependent transmission and filtering properties required of the output mode cleaner depend on the ISC readout scheme chosen (DC or RF) and will be determined in an integrated manner with the choice of the readout scheme.

The photon actuator employs an auxiliary laser beam that is reflected from the optic to be actuated upon; the laser amplitude is modulated to control the radiation force. Lasers of several watts can deliver the very small forces required.

R&D Status/Development Issues

Development of active optic thermal compensation is proceeding under the LIGO advanced R&D program. A model of the thermal response of the interferometer in a modal basis has been developed55 and used extensively to make predictions for the deformations and of the possible compensation. A prototype has successfully demonstrated thermal compensation, in excellent agreement with the model, using both the ring heater and directed laser techniques56. A detailed characterization of the spatial distribution of absorption in Sapphire is needed to quantify the correct approach for Advanced LIGO; this will be available from the Core Optics Components test articles in early 2003. This will be complemented with a physical optics model using FFT beam propagation techniques, using these phase maps as input.

The photon actuator will require a more complete systems model for the dynamic range and frequency response to be precisely defined. The intensity stabilization of the source laser is likely to present the only challenge, but present models do not indicate difficulty with the design.

There are two potential designs for the output mode cleaner, dependent on the chosen gravitational wave readout technique. If RF sidebands are used, then the output mode cleaner will be effectively a copy of the input mode cleaner, as it must pass efficiently both the carrier and sidebands. If DC readout were used, the output mode cleaner would be a short, rigid cavity, mounted in one of the output HAM chambers. Both the VIRGO Project and GEO-600 use output mode cleaners in their initial design. We plan to start with a study of their approach and the experience with those systems. The principal design challenges lie in the interface to the Interferometer Sensing and Control. The cavity must be aligned with the nominal TEM00 axis of the interferometer, but the bulk (by several orders of magnitude) of the output power will be in higher-order modes; determining the correct alignment is thus non-trivial. The length control, in particular the lock acquisition sequence, also adds complexity.

Work Plan

Work on the active optics thermal compensation is proceeding under the advanced R&D program. A complete prototype thermal compensation system will be tested in the ACIGA Gingin facility in 2003. A prototype photon actuator is being developed with a test on the Caltech 40

55 R.G.Beausoleil, E. D'Ambrosio, W. Kells, J. Camp, E K.Gustafson, M.M.Fejer: Model of Thermal Wavefront Distortion in Interferometric Gravitational-Wave Detectors I: Thermal Focusing, to appear in JOSA B; http://arxiv.org/abs/gr-qc/0205124 56 Adaptive thermal compensation of test masses in Advanced LIGO, R. Lawrence, M. Zucker, P. Fritschel, P. Marfuta, D. Shoemaker, Class. Quant. Gravity 19 (2002)

83 LIGO M030023-00M

Meter Interferometer prototype planned for 2004. The output mode cleaner will be studied using the modeling tools developed for the Mode Cleaner cavity (to which this may bear a strong resemblance) and overall interferometer controls models; a small-scale tabletop prototype will be developed if indicated to ensure that the models are complete to support the ISC design schedule (with a Preliminary Design Review in mid-2004), with the design and fabrication profiting from the suspension and core optics groups. The design process for the beam dumps, baffles, reducing telescopes will resemble that for the initial LIGO design with a planned installation starting in 2007.

84 LIGO M030023-00M

12. Interferometer Sensing and Controls Subsystem (ISC)

Overview

This subsystem comprises the length sensing and control, the alignment sensing and control, and the overall controls infrastructure modifications for the Advanced LIGO interferometer design. The infrastructure elements will be modified to accommodate the additional control loops in the reference design. The single most significant difference in the Advanced LIGO subsystem is the addition of the signal recycling mirror and the resulting requirements on the controls.

Functional Requirements

Table 7 lists significant reference design parameters for the interferometer length controls.

Table 7 Significant Controls Parameters

Configuration Signal and power recycled Fabry-Perot Michelson interferometer Controlled lengths • differential arm length (GW signal) • near-mirror Michelson differential length • common-mode arm length (frequency control) • power recycling cavity resonance • signal recycling mirror control Controlled angles 2 per DOF above, 12 in total Main differential control requirement 10-14 m rms Shot noise limited displacement sensitivity 4×10-21 m/√Hz

Angular alignment requirement 10-9 rad rms

The requirements for the readout system are in general more stringent than those for initial LIGO. The differential control requirement is a factor of 10 smaller, as is the angle requirement, and the additional degrees of freedom add complexity. Integration with the thermal compensation system and the gradual transition from a “cold” to a “hot” system will be needed.

In spite of the increased performance requirements for Advanced LIGO, significant simplification in the controls system is foreseen because of the large reduction in optic residual motion afforded by the active seismic isolation and suspension systems. Reduced core optic seismic motion can be leveraged in two ways. First, the control servo loop gain and bandwidth required to maintain a given RMS residual error can be much smaller. Second, the reduced control bandwidths permit aggressive filtering to block leakage of noisy control signals from imperfect sensor channels into the measurement band above 10 Hz. While control modeling is just getting started, this latter benefit is expected to significantly relieve the signal-to-noise constraints on sensing of auxiliary length and alignment degrees of freedom.

Concept/Options

85 LIGO M030023-00M

The signal-recycled configuration is chosen to allow tunability in the response of the interferometer. This is useful for the broadband tuning to control the balance of excitation of the mirrors by the photon pressure, and the improvement in the readout resolution at 100-200 Hz. A narrow-band instrument (to search for a narrow-band source, or to complement a broad-band instrument) can also be created via a change in the signal recycling mirror transmission. An example of possible response curves for a single signal recycling mirror transmission is shown in Figure 25.

Another important advantage of the signal recycled configuration is that the power at the beamsplitter for a given peak sensitivity can be much lower; this helps to manage the thermal distortion of the beam in the beamsplitter, which is more difficult to compensate due to the elliptical form of the beam and the significant angles in the substrate.

-21 10

-22 10 1/2 -23 10

h(f) /Hz s app hir e th erm oe las -24 tic 10 no ise

-25 10 1 2 3 10 10 10 Frequency (Hz) Figure 25 Strain sensitivity curves for a narrowband interferometer. With a single signal recycling mirror chosen to give optimum performance around 700 Hz, good performance between ~500–1000 Hz can be achieved by tuning the signal mirror position microscopi- cally; the set of curves shown span a mirror motion of about 0.01 wavelength. At the lower end of the octave, sapphire’s thermoelastic noise limits the performance; at higher frequencies, above ~500 Hz, sapphire has a clear advantage over fused silica for narrowband performance (modeled using Bench57)

Most length sensing degrees-of-freedom will be sensed using RF sidebands in a manner similar to that in initial LIGO. There are two options for the main gravitational readout. One is to use an RF system similar to initial LIGO, in which variants of the Pound-Drever-Hall scheme are used to derive zero-crossing error signals. The other is to shift the output of the interferometer slightly away from the dark fringe and to use deviations from the setpoint as a measure of the strain. This approach considerably relaxes the requirements on the laser frequency; the nominally more stringent requirement on the baseband intensity fluctuations appears tractable. Two

57 L. S. Finn, http://gravity.psu.edu/~lsf/Benchmarks/main.html

86 LIGO M030023-00M considerations will inform the choice of approach: (i) A complete quantum-mechanical analysis of the two readout schemes to determine which delivers the best sensitivity; and (ii) Requirements imposed on the laser and modulation sources due to coupling of technical noise.

Alignment sensing and control will be accomplished by wavefront sensing techniques similar to those employed in initial LIGO.

The much lower seismic noise in Advanced LIGO will allow smaller control bandwidths for the test-mass actuators; on the other hand, forces to keep the system stable against photon pressure will need to be exerted. In general, the active isolation system and the multiple actuation points for the suspension provide an opportunity to optimize actuator authority in a way not possible with initial LIGO, but will also lead to a more complex system for initial acquisition of operation (“locking”) as well as during operation.

R&D Status/Development Issues

The signal-recycled optical configuration chosen for Advanced LIGO (see Figure 14) challenges us to design a sensing and control system that includes the additional positional and angular degrees of freedom introduced by the signal-recycling mirror. Several straightforward extensions of the sensing system for initial LIGO have been considered. Mason58, Delker59 and Shaddock60 have demonstrated locking of signal-recycled tabletop interferometers using variants of the initial LIGO asymmetry method, adapted in more or less radical ways to accommodate the additional signal recycling cavity degrees of freedom.

These tabletop experiments and their associated simulations have shown that it is not difficult to arrive at non-singular sensing schemes by adding an additional RF modulation which, through selection of resonant internal lengths, preferentially probes the new cavity coordinates. However there is a great deal of subtlety in choosing parameters to decouple the coordinate readouts adequately to establish a simple, robust control design while realizing the high strain signal-to- noise required.

A detailed prototype test of the control system is underway in GEO (Glasgow), with results expected in early 2003. An engineering control demonstration is in preparation in the LIGO 40 Meter Interferometer (Caltech); it will be fed with information from the GEO effort, and will strive to make a complete emulation of the control system using the target control hardware and software. Locking and operation of the system will be studied.

The selection of the readout scheme involves a trade-off between optimal signal detection and sensing noise (of both fundamental quantum origin and technical noise). The signal-recycling mirror, detuned from perfect resonance, generates a coupling between the shot noise and the mirror motion induced by radiation pressure noise. This causes the GW signal to appear simultaneously in both the phase and amplitude quadratures of the output field (a significant departure from initial LIGO and other first-generation detectors). The DC and RF readout

58 J. Mason, “Length Sensing and Noise Issues for a Advanced LIGO RSE Interferometer,” PAC Meeting, 1 May 2000 (http://www.ligo.caltech.edu/docs/G/G000119-00.pdf) 59 T. Delker, G. Mueller, D. Tanner, and D. Reitze, “Status of Prototype Dual Recycled-Cavity Enhanced Michelson Interferometer,” LSC Meeting, 15 Aug 2000 (http://www.ligo.caltech.edu/docs/G/G000275-00.pdf) 60 M. Gray, D. Shaddock, C. Mow-Lowry, and D. McClelland, “Tunable Power-Recycled RSE Michelson Interferometer for Advanced LIGO.” LSC Meeting, 15 Aug 2000 (http://www.ligo.caltech.edu/docs/G/G000227-00.pdf)

87 LIGO M030023-00M schemes respond to the frequency-dependent optimal signal quadrature differently and the goal is to find a best compromise61.

To accommodate the needs for wideband multi-frequency auxiliary length readouts, the DC strain readout, and high-frequency wavefront sensing, characterization of photodiodes will be undertaken. As for initial LIGO detectors, the first steps will be surveys of commercial devices and those developed by colleagues in other projects. This phase will likely be followed in one or more cases by development work to customize or to improve performance and to optimize the electronic amplifiers that mate to these detectors.

Though not necessarily required, lower noise analog-to-digital and digital-to-analog converters would be of great benefit in the design of the sensing and control signal chain. We will prototype board circuitry and software to integrate these converters into our VME-based digital control environment. We also will experiment with new topologies and circuits for the critical analog signal conditioning filters that match the dynamic range of the converters to that of the physical signals they deal with.

Work Plan

The controls configuration will be developed based upon the experience gained from the use of signal recycling in the GEO 600 interferometer, experiments conducted at several institutions in the LSC including pivotal work at the GEO 10 meter prototype from which results are due in early 2003. The final test takes place in the Caltech 40 Meter Interferometer for which the construction will be complete in late 2003; it will inform the design in mid-05, and fabrication can start shortly thereafter. The LIGO Laboratory will manage the design and fabrication of the controls subsystem as it did during initial LIGO construction.

61 A. Buonanno, and Y. Chen, “Quantum noise in second-generation signal-recycled laser interferometric gravitational wave detectors,” Phys. Rev. D 64, 042006 (2001); A. Buonanno, Y. Chen, and N. Mavalvala, “Quantum noise in laser interferometer gravitational wave detectors with a heterodyne readout scheme," to be submitted to Phys. Rev. D (2003), P020034-00-R

88 LIGO M030023-00M

13. Data Acquisition, Diagnostics, Network & Supervisory Control (DAQ)

Overview

The differences between the initial LIGO and Advanced LIGO Data Acquisition, Network & Supervisory Control (DAQ) requirements derive from the improved sensitivity and performance of the Advanced LIGO interferometers. We specify an increased ADC dynamic range to more easily accommodate the great disparity between narrowband features and lower broadband noise, and a greater number of channels to monitor a greater number of active control systems

Functional Requirements

The principal Advanced LIGO reference design parameters that will drive the data acquisition subsystem requirements are summarized in Table 8.

Table 8 Principal impacts of the Advanced LIGO Reference Design on Data Acquisition and Data Analysis Systems. The number of Degrees of Freedom (DOF) is indicated for the main interferometer to give a sense of the scaling.

Parameterization Advanced LIGO Initial LIGO Comment Reference Implementation Design Whitened h[t] > 121 dB 96 dB Range of h[t] is determined by dynamic range (20 bits) (16 bit ADC) narrowband feature amplitude and broadband noise floor. Acquisition System 16384 16384 Effective shot noise frequency Maximum Sample cutoff is well below fNyquistt Rate, s/s (8192 Hz) Active cavity 7 6 Signal Recycling Mirror will be mirrors, per added. interferometer Active seismic 11 chambers per 2 end chambers Iinitial LIGO uses passive isolation system interferometer; 18 per isolation with an external 6 DOF servos DOF per interferometer, pre-isolator on end test masses; chamber; total, total, 12 DOF Advanced LIGO uses active 198 DOF multistage 6 DOF stabilization of each seismic isolation platform. Axial and angular SUS DOF : 42 SUS DOF: 36 Advanced LIGO has two alignment & L DOF: 5 L DOF: 4 additional cavities. Each control, per (θ, φ ) DOF:12 (θ, φ ) DOF: 10 actively controlled mirror interferometer requires 6 DOF control of (4 km / 2 km) suspension point plus (θ, φ, L ) control of the bottom mirror. Total Controlled 257 62 Relative comparison of servo DOFs loop number for maintaining resonance in the main cavities (PSL and IO not included)

The reference Advanced LIGO design will have a broadband noise floor between narrowband features that is limited by radiation pressure noise at a level h[f]~2-3 10-24 1/√Hz (see Figure 15), ~ 10x lower than the initial LIGO design. Our present best estimate is that the Advanced LIGO

89 LIGO M030023-00M dynamic range requirement for whitened signals at the interferometer output port will be ~ 10x greater than the initial LIGO baseline, leading to a working requirement for ADC resolution of 20 bits.

Advanced LIGO will require monitoring and control of many more degrees of freedom (DOF) than exist in the initial LIGO design. The additional DOFs arise primarily from the active seismic isolation, with a smaller contribution from the move to multiple pendulum suspensions and the additional suspended mirror. Table 8 summarizes these modifications. Both the suspension and the seismic isolation systems will be realized digitally (except for the sensors and actuators) and the DAQ will need to capture a suitable number of the internal test points for diagnostics and state control (as is presently done for the initial LIGO digital suspension controllers).

Referring to Table 8, the number of loops per interferometer that are required for Advanced LIGO is seen to be ~ 250. This is to be compared to ~ 60 for initial LIGO. The number of channels that the DAQ will accommodate from the interferometer channels for Advanced LIGO will reflect this 4X increase in channel number.

Table 9 presents approximate channel counts classified by sample bandwidth for Advanced LIGO and compares these to initial LIGO values. These represent the total volume of data that is generated by the DAQS + GDS; a significant fraction of these data are not permanently acquired. Nonetheless, the ability to acquire all available channels must be provided.

Table 9 DAQ Acquisition Data Channel Count and Rates62

System Advanced Initial LIGO63 Comments LIGO Reference Design Channels, LHO + LLO 5464 + 3092 1224 + 714 LIGOII will have ~4.5X Total 8556 1938 greater number of (Total: 3 x IFO + 2 x PEM) channels. DAQS II has ~3X total data Acquisition Rates, MB/s 29.7 + 16.3 11.3 + 6.1 acquisition. LHO + LLO 46 17.4 Total

Recorded Framed Data DAQS II has ~2X total Rates, MB/s framed data recording rate. LHO + LLO 12.9 + 7.7 6.3 + 3.5 Total 20.6 9.8

Concept/Options

The driving features of the Advanced LIGO hardware design are the increase in channel count and increase in data word length for the main sensing channels. The initial LIGO 16 bit ADCs will be exchanged for newer 32 bit ADCs (note: 20 bits are actually specified). Not all DAQS channels require the greater dynamic range. Moreover, the increase in acquisition bandwidth with double data-word size dictates that only those channels requiring the increased dynamic range should be upgraded.

62 These rates include are derived from LIGO I rates with scaling as indicated in the table. Data rates quoted include a number of diagnostics channels and this rate is greater than the framed data rate which eventually is recorded for long term storage. 63 LIGO I channel counts differ by site and interferometer; representative values are indicated.

90 LIGO M030023-00M

The additional data channels required for the newer seismic isolation and compound suspension systems will require additional ADCs distributed throughout the LVEA and VEA CDS racks. Additional racks will be required and can be placed alongside the present CDS racks within the LVEA and VEAs. In those cases where there is interference with existing hardware, racks will need to be located further away, at places previously set aside for LIGO expansion. Additional cable harnesses for new channels will be accommodated within the existing cable trays.

The initial LIGO DCUs do not have excess capacity sufficient to accommodate the increase in acquisition rate and will need to be upgraded. The upgrade will be a combination of updating the hardware technology and using a greater number of DCUs. The existing fiber optic infrastructure will accommodate the Advanced LIGO DAQS changes without requiring an upgrade. The DAQ framebuilder and on-line mass storage systems will be upgraded to accommodate the greater data and frame size. The Global Diagnostic System (GDS) will be upgraded to handle ~3X as much real time data as the initial LIGO GDS.

R&D Status/Development Issues

At present, ADC technology is not capable of providing full 20-bit ADC precision at output rates of 16384 samples per second. Our experience indicates that the principal limitation is likely the ADC board design that uses the 24-bit ADC chip, and we may need to develop in-house or collaborative solutions with industry to meet our stringent requirements. Additional performance limitations may also come from the VME format of the boards that initial LIGO uses. The VME bus is a very noisy environment that may limit ADC performance, and we will study alternatives such as VXI for sensitive parts of the design.

This will require new solutions to be identified and prototyped to determine performance of candidate hardware solutions. Much of this type of work will be performed by using the 40 Meter Interferometer at Caltech, which is designed to exercise the hardware and software environment for Advanced LIGO.

Similarly, the GDS hardware will need to be scaled for the greater processing and throughput requirements. Parallelization techniques that are being used in the LDAS I design (e.g., passing messages across Beowulf clusters) can be introduced to solve compute-bound (but not I/O bound) data processing problems.

It is plausible that hardware technology trends will continue over the next 5 years. Thus, it is likely that the solutions required to support the ~3X increased acquisition rates and data volumes would become commercially available by the time they are needed. We have taken as the point of departure that “Moore’s law” will be a reasonable predictor of the growth in available performance.

Work Plan

The first phase will develop a detailed set of requirements for the DAQ upgrade. These will proceed with the development of a Design Requirements Document and a Conceptual Design. Activities that begin in this phase include the development and refinement of an Advanced LIGO model. This will produce a curve of strain sensitivity goal with sufficient details so that issues of dynamic range, etc. can be addressed with simulation to guide the hardware design. As refined design information for new SEI, SUS, and ISC subsystems becomes available, the channel count estimate and their sampling rates will be improved.

The second phase will incorporate results from prototyping. Preliminary board layouts for custom components will be developed as part of this stage. The procedures by which the existing plant

91 LIGO M030023-00M will be de-integrated and the newer components introduced will be identified. Software development associated with DAQ II modifications of the DAQ I plant and infrastructure will begin.

The third phase will culminate in a detailed set of drawings, specifications, and procurement or fabrication plans for the DAQ II equipment. Fabrication will follow, and it is anticipated that this phase will be carried out primarily by the LIGO Laboratory staff as it was during initial LIGO construction.

92 LIGO M030023-00M

14. Support Equipment (SUP)

Overview

Installation of seismic isolation and suspension subsystems in multiple vacuum chambers at both sites will require an increase in basic materials handling equipment. These include additional forklifts, general purpose rigging hardware, personnel lifting devices (of the “Genie-lift” type), and general-purpose hand tools suitable for use in an ultra-clean environment. Some of this equipment is also required for assembly of the seismic and suspension units prior to installation.

Functional Requirements

All requirements match those used to select similar equipment for initial LIGO construction.

Concept/Options

There are no significant options in this element.

R&D Status/Development Issues

There are no significant issues in this element.

Work Plan

Procurement of the required support equipment must be completed prior to assembly operations in 2006, and installation activities in 2007.

93 LIGO M030023-00M

15. Advanced LIGO Construction Project Research and Development (R&D)

Overview

All identified R&D issues are included in the Advanced R&D program supported by NSF, current LSC activities, or planned development activities supported within the LIGO Laboratory Operations budget (WBS 2.0). In general, the separately funded Advanced R&D program brings all subsystems to the point of the completion of the Design Requirements, the Conceptual Design, and through significant prototyping. The few exceptions are where no R&D is needed, and the requirements and conceptual design are very similar to initial LIGO. At present, there are no activities planned for R&D in the Construction Project phase.

Functional Requirements

TBD

Concept/Options

TBD

R&D Status/Development Issues

TBD

Work Plan

TBD

94 LIGO M030023-00M

16. Data Analysis and Computing Subsystem (COMP)

Overview

The Advanced LIGO data analysis computational load is increased over that for initial LIGO due to the broader range of detector sensitivity. The features of initial LIGO and Advanced LIGO sensitivities that impact astrophysical data analysis are summarized in Table 10. The frequency at optimum sensitivity is fmin= 130 Hz in initial LIGO and roughly at this same frequency (dependent upon the signal tuning) for Advanced LIGO. However, the Advanced LIGO optimum sensitivity will be roughly a factor 10 better, leading to an increased range for detection of 10. The enhanced frequency range for Advanced LIGO means that sources whose characteristic frequency of emission varies with time will be observable in the detection band for longer periods. Combined, these enhancements – greater range and in-band dwell time – imply that the rate of detectable events with Advanced LIGO will be orders of magnitude greater than initial LIGO. Projected event rate increases, estimated through scaling laws and anticipated signal signatures38, are discussed in the section “Reference Design Sensitivity Goal” on page 47

Table 10 Key Parameters of the Advanced LIGO Reference Design That Affect the Data Analysis System

Parameterization Advanced LIGO Initial LIGO Comment Reference Design Implementation

Effective Seismic fsei ~ 20 Hz fsei ~ 40 Hz Point at which Cutoff Frequency h[fsei] = 10 h[fmin]

Frequency at Fmin ~ 130 Hz fmin ~ 130 Hz Minimum of h[f] does not Optimum Sensitivity change between initial LIGO and Advanced LIGO -1/2 -24 -23 h[fmin], Hz 2-3x10 3x10 - (tuning dependent) Data sample word 4 2 Determined by increased length [bytes] for dynamic range key channels

Maximum Sample Upper cutoff, fshot, is well Rate, s/s 16384 16384 below fNyquistt for both fNyquistt, Hz 8192 8192 initial LIGO and II

95 LIGO M030023-00M

The impact of exploiting the increased source detection ability on data analysis strategies and the initial LIGO Data Analysis System depends on the source type being considered and will be discussed by source type below. Most presently envisioned search and analysis strategies involve spectral-domain analysis and optimal filtering using template filter banks calculated either from physics principles or parametric representations of phenomenological models. The primary channel that is useful for astrophysics is the instrumental output that is proportional to strain. All the other thousands of channels in initial LIGO and Advanced LIGO are used to validate instrumental behavior. It is also expected that relatively few channels (< 10) will prove useful in producing improved estimates of GW strain. This would be done by removing instrumental cross- channel couplings, etc. either with linear regression techniques in the time domain (Kalman filtering) or in the spectral domain (cross-spectrum correlation). We assume here that signal conditioning will not be a driver for LDAS II upgrades. This is certainly the case for LDAS I and there is no reason to expect this to change.

Anticipated sources of gravitational waves may be classified by the frequency vs. time (t-f) behavior of the gravitational radiation waveforms they produce. Transient or burst phenomena have short duration (0.1 s – 2s) and have relatively broad frequency content during this short time. The t-f signature of a burst is a vertical “stripe” spanning many frequencies over a narrow time slice. Starting from 10 Hz and continuing through coalescence, compact object binary inspirals have durations that will be ~1 s for the most massive systems, ~1000 s for 1.4 solar- mass neutron-star, and ~ 26000 s systems composed of objects at the theoretical limits of NS masses. Their waveform comprises a periodic signal with a time dependent frequency that produces a “chirp” which starts at the low end of the detection band and which crosses the band during the time quoted. Their t-f signature corresponds to a curved (“banana-like”) trajectory such that at each instant in time the waveform has a well defined and monotonically increasing frequency. Continuous wave periodic sources (i.e., pulsars emitting GW) have very precisely defined frequencies that have secular variations over hours or days. The secular variation contains a deterministic component coming from motion of the earth about the Solar System barycenter and possibly other, a priori unknown, components arising from motion of the source in its own orbit. The t-f signature of a CW source is a horizontal “stripe” spanning a narrow frequency range for all times, with the frequency modulated by the Earth’s complicated motion with respect to the source. Finally the stochastic background GW radiation spans many frequencies for all times, and is detected via an excess of the correlation of 2 or more detectors for zero time lag. Corresponding to each of these t-f behaviors there is an optimal search strategy, and each of these has significantly different computational costs.

Functional Requirements Computational Upgrades

For the classes of sources considered (transient “bursts”, compact object inspirals, stochastic backgrounds, and continuous-wave sources), the binary inspirals place the greatest demands on the computational infrastructure. Advanced LIGO will search for compact object binary inspiral events using the same technique that will be employed in initial LIGO: a massive filter bank processing in parallel the same data stream using optimal filtering techniques in the frequency domain. The extension to lower frequencies of observation allowed by Advanced LIGO means that the duration of observation of the inspiral is significantly longer, leading to a concomitant increase in the computing power required.

Referring to Table 11, one sees that the baseline initial LIGO can search to 0.7MO• systems, and this involves chirps lasting ~72 s. This increases to ~888 s in Advanced LIGO for 0.5MO• systems. The length of the chirp sets the scale of FFTs that are required for optimal filtering. FFT computational cost scales as ~N log2N. On the other hand, the greater duration of the chirp

96 LIGO M030023-00M provides more time to perform the longer calculation. Together a ~12X increase in signal duration corresponds to a ~3X increase in computational cost.

Each observatory (Hanford, Livingston) has an on-site Beowulf system. The Hanford component of LDAS handles two interferometers and is designed to be 2X as capable in terms of CPU FLOPS as the one at Livingston (some components do not scale and are essentially identical at both sites). The quantities appearing in Table 11 correspond to the Hanford site operating with two interferometers. Table 12 lists the main features of the parallel cluster at Hanford.

Anticipating Moore’s Law for computer hardware development to continue over the next 5 years, the ~ 3X – 4X improvement which will enable Advanced LIGO to search down to 0.5 MO• can be accomplished within the expected technology envelope. Advanced LIGO will upgrade the on-site computational facilities at both observatories to provide capacity to search for low-mass binaries.

97 LIGO M030023-00M

Table 11 Initial LIGO and Advanced LIGO Analysis System Requirements for Compact Object Binary Inspiral Detection Using Wiener Filtering Techniques. M=1MO• provides a reference to indicate how quantities change with Mmin. Quantities were calculated using a spreadsheet model of the data flow for the inspiral detection analysis pipeline, and assume a 20 Hz start frequency for observation.

Parameter Advanced LIGO Initial LIGO (LHO) Comment (LHO) 1MO• /1MO• 0.7MO• 1MO• /1MO• 0.5MO• /0.7MO• /0.5MO• Maximum template 280 s 888 s 44 s 72 s Initial LIGO length, seconds can search to 0.7 M Maximum template 4.6 MB 15 MB 720 kB 1.3 MB O•

length, Bytes Advanced Number of templates 9×103 6×104 9×103 2.4×104 LIGO can search to Calculation of ~0.1 ~0.7 ~0.1 ~0.3 0.5 M templates, FLOPS GFLOPS GFLOPS GFLOPS GFLOPS O• Storage of templates, 84 GB 2 TB 13 GB 63 GB Bytes Wiener filtering 9 35 5 13 analysis, FLOPS GFLOPS GFLOPS GFLOPS GFLOPS

Table 12 Initial LIGO and Advanced LIGO Analysis System Specification for Compact Object Binary Inspiral Detection Using Wiener Filtering Techniques.

Parameter Advanced Initial LIGO Comment LIGO Beowulf Cluster Size 256 96 Initial LIGO can search (# nodes @ LHO) on-site to Memory per CPU, MB 1280 256 0.7 MO• with ~ 80% Disk per node, GB 18 4 excess capacity. Advanced LIGO can MFLOPS per node 500 230 search on-site to Total Computational 36 13 0.5 MO• with ~ 250% Power, GFLOPS excess capacity

The off-site computing facilities at Caltech support analysis and data storage and retrieval functions. The parallel Beowulf cluster at Caltech will also be upgraded to provide expanded search and analysis capacity. For example, binary inspiral searches below 0.5 MO• become very expensive and will be performed at a single site, using data from all interferometers. The Caltech Beowulf cluster will be increased from the planned initial LIGO size of 144 nodes to 512 nodes.

Data Archival/Storage Upgrades

By far the biggest impact on LDAS II will be in the area of data handling and storage. This is because, as discussed above, the dramatic enhancements in Advanced LIGO have only modest impacts on the data analysis. Yet, the shear volume of additional data which are associated with monitoring the much more complex interferometers must be accommodated, at least until data QA can be performed to discard unneeded channels.

98 LIGO M030023-00M

Below, we assume the initial LIGO data use and storage model will continue. It will be validated and revised as actual experience accrues during the initial LIGO data analysis run. In this model, all data are acquired and stored for some ~72 hours on-line in a disk cache. Then the data are staged to tape media. Two copies of tapes are produced. One copy is held on-site for ~30 days. The other copy is sent to Caltech where data reduction takes place in the form of removing channels that pass certain QA tests and replacing large volumes of data from many channels with data QA indicators. The target in initial LIGO will be a 10X reduction in raw data volume. We expect ~3X to come from loss-less compression (both in hardware within the tape drives and algorithmically in filters). Another ~3X will come from re-sampling and reduction in the number of channels which are permanently archived.

We have scaled from initial LIGO values using the nominal ~3X increase in data acquisition rate that was identified in 13. Data Acquisition, Diagnostics, Network & Supervisory Control (DAQ).

Handling Greater DAQ II Data Rates – Frame Data Archive Growth

There will be a ~ 3X increase in the rate with which DAQS II generates framed data from the interferometer and PEM subsystems. These data will be accommodated for periods of ~16 hours on spinning media. The corresponding volume of data that must be accommodated is ~1 TB. The on-site disk cache for Advanced LIGO will require expansion to 2 TB. This volume represents ~100% margin for additional growth, which is comparable to the initial LIGO design.

In addition, the on-line data will need to be backed up continuously onto tape media. The full frame data are recorded and sent off-site (where compression and reduction takes place). Hanford LDAS II will be upgraded allow transfer to tape at rates of 21 MB/s, and 11 MB/s at Livingston.

The Caltech permanent archive will also need to be upgraded; Advanced LIGO will require a ~ 600 TB archive at Caltech.

Handling Greater Event Rates – Metadatabase Growth

The LIGO metadatabase serves to provide logging of diagnostics triggers that come from real- time monitoring of the interferometer and PEM channel, and to provide for logging of frame data and candidate astrophysical events. Depending on the levels of compression that are ultimately achieved on the raw framed data, metadata generated from frames (trends, histories, etc.) will grow directly as the volume of frames. If this is assumed to grow by ~3X, then Advanced LIGO will require an increase of 3X in storage and serving capacity for frame summary metadata at the Caltech server.

Wide Area and Local Area Network Upgrades

The increased volume of data generated can be reasonably expected to generate a concomitant need to provide increased internet connectivity between the observatories and Caltech and in general to the larger LSC community. By the time of the initial LIGO science run, it is expected that the observatories will be connected to Caltech at OC3 bandwidth, although it is likely that LIGO will not have access to the full bandwidth (Hanford shares ESnet resources; Livingston shares LSU resources). Therefore Advanced LIGO will require an upgrade to the connectivity to provide to LIGO Laboratory full ATM access between observatories and Caltech.

Software Upgrades

99 LIGO M030023-00M

The LDAS I infrastructure is designed to be expanded and upgraded by use of object-oriented programming (OOP) and of a distributed computing paradigm in its design. The data analysis software will need to be ported to newer and greater numbers of hardware platforms. In some cases, certain interfaces may need to be expanded to accommodate the greater level of distributed computing being foreseen.

The biggest impact to LDAS software design will be in the area of database management systems to handle the greater quantity of data and a growing community of users. Advanced LIGO will require a greater database size, more powerful and more numerous servers, and a federated implementation of the database system. It is likely that the currently used IBM DB2 may need to be replaced with a more powerful DBMS (e.g., Oracle, OBJECTIVITY or one of its newer derivatives, or an upgrade of DB2) that is fully object-oriented. Therefore, the LDAS I DBMS infrastructure and paradigm will need to be upgraded for Advanced LIGO.

Concept/Options

The implementation of LDAS II is a more or less straightforward expansion of LDAS I. This is largely possible because of the highly modular, API-specific, object-oriented paradigm that initial LIGO is implementing.

Additional PC clusters will be added to or replace existing clusters. LAN network infrastructure in place for initial LIGO will be capable of expansion to accommodate 4X bandwidths by combinations of multiple connections (e.g., an increased number of ATM fabrics) and higher bandwidth (OC12 or OC48). Network-based RAID disk systems are planned for initial LIGO and will be expanded or replaced with improved versions of similar systems (later generation, larger disk volumes, etc.). These disk systems will support growth of both metadatabases and framed databases. Data servers will be upgraded to Enterprise class servers available at the time. Multiple servers may be clustered to provide greater throughput where this is required.

Tape archive robotic systems will be upgraded or replaced. The 4X growth of the local short-term archives at the observatories will require installation of SAM-QFS or a similar software environment on the archive server at the sites. The Caltech archive shall be expanded to accommodate the greater volume of Advanced LIGO data. Tape drives capable of writing data at the acquisition rate of ~ 21 MB/s (Hanford) do not exist today, but their development or a workaround can be anticipated.

WAN access to LIGO data will be provided from each observatory and Caltech at then current ATM (OC3/OC12/OC48) or Ethernet (1000BT) bandwidths.

R&D Status/Development Issues

Most of the improvements in hardware performance that are discussed and identified above should become naturally available through the advance in technology that comes from market forces. LIGO will continue to meet its needs using commercial or commodity components.

100 LIGO M030023-00M

Work Plan

A Design Requirements and Conceptual Design Review (DRR) will take place once the key functional requirements have been identified. The conceptual implementation is designed to develop a credible basis on which the upgrades can be planned and built. It also serves to firm up projected budgets and to identify any design changes that were unforeseen at the time of the proposal. This review should take place within the first year of inception of LDAS II work.

Based upon initial LIGO experience, a Preliminary Design Review (PDR) will take place approximately one year after the DRR. The concept described in the DRR is “fleshed out” to the point where it is reasonably certain that there are no “show stoppers” in the proposed implementation approach. Hardware solutions are identified; software implementations are prototyped; prototyping results for computational costs, data access times, storage volumes, etc. will generally become available during and immediately after this review stage.

A Final Design Review will take place approximately one year after the PDR. At this point, the detailed procurements list and design for how each of the upgrades takes place will be completed. Plans will be developed for how LDAS I components will be decommissioned and replaced with Advanced LIGO components from initial prototypes through to the operational systems. After this juncture, complete implementation will begin and continue for 1 – 2 years.

101 LIGO M030023-00M

17. Installation and Commissioning Task (INS)

Overview

The installation and commissioning of the Advanced LIGO detector systems is planned to be as rapid as possible in order to minimize the observatory downtime. It requires the installation of all detector elements in all three LIGO interferometers in a phased approach to best utilize the infrastructure and manpower in the Laboratory and LSC. The subsystem teams are expected to have pre-assembled and pre-tested components available for installation when needed (some assembly and test can take place at the observatory sites in advance).

Functional Requirements

At the end of the installation and commissioning period Advanced LIGO should be running reliably near design sensitivity. The installation and commissioning effort must be done simultaneously with continued observatory site and LIGO Laboratory operations, though much of the staff will be diverted to installation and commissioning tasks.

Concept/Options

The basic conceptual plan for the installation is as follows:

• The installation and commissioning phase is under the direction and responsibility of the LIGO Laboratory. LSC members may contribute and assist. We assume that developers of technology in the LSC will participate in installation and commissioning of their respective components, though our planning assumes much of the labor required will come from the Laboratory staff or contractors. • Full-scale subsystem testing is performed to prove out the design and fabrication of components, assemblies and subsystems and their interfaces wherever possible. • System level testing of the full configuration (power and signal recycled Michelson with Fabry-Perot arm cavities) with as much of the full-scale hardware as possible (active seismic system, suspension system, etc.) is performed on the Caltech 40 Meter Interferometer and MIT LASTI testbeds. • Installation exercises will be carried out for the major mechanical subsystems at the MIT LASTI testbed, training the subsystem and observatory staff who will then carry our the installation at the observatories. • Pre-assembly, pre-alignment and pre-testing (to the extent possible) is carried out for all subsystems prior to installation into the system. For example, the seismic systems will be fully preassembled and sealed for transport from onsite staging buildings into the vacuum equipment areas. Suspensions will be preassembled onsite up to attachment of the final silica fibers and test masses. These will be installed at the time the vacuum system is ready to receive the subsystems. • In order to minimize observatory downtime, installation will not begin until all required fabrication is complete and all required assembly and unit level testing is complete. • Two shifts of installation are planned only for labor-intensive activities on the critical path and held in reserve for contingency for non-critical tasks. • The commissioning teams, as in initial LIGO, require expertise from multiple disciplines and subsystems. Staffing for the design and development phases of the Advanced LIGO effort are planned with the intent of providing this expertise.

One possible option in the overall program, which has significant impact on the installation and commissioning phase, is whether the initial LIGO 2 km interferometer is converted to a 4-km

102 LIGO M030023-00M interferometer or operated in the initial LIGO configuration. The baseline for this proposal is that the 2km interferometer will be upgraded and the arm length will be extended to 4 km.

R&D Status/Development Issues

A rapid and predictable installation schedule requires well thought out and tested installation procedures and fixtures. LASTI will provide an opportunity to test these installation procedures in full-scale chambers and to train team leaders. This development is essential for successful installation of the interferometers.

System R&D and testing of the signal and power recycled configuration on the 40 Meter testbed is essential for the commissioning team to gain the experience and expertise that will be required.

Work Plan

In early 2007, the three initial LIGO interferometers will complete their coincident observation run and the Livingston instrument will be turned off. This event will trigger the start of installation activities. For many months prior to this point, the subsystem components will have been pre- positioned at the sites, assembled and tested, and the limiting pace should be set by the available skilled manpower. Near the end of 2007, the initial LIGO Hanford instruments will be turned off. The seismic isolation installation will be completed at Livingston by that time, and that installation team will migrate to Hanford for the commencement of installation there. This staggered pattern will continue with the suspensions, optics, and the other subsystems.

This is the baseline plan. The status of the global observing networks, agreements between projects, and scientific and technical developments may motivate altering the order of upgraded interferometers or the interval between installations of the successive interferometers.

The plan is to perform the physical installation as rapidly as possible to maximize the time for debugging, characterization and commissioning. This is enabled by the pre-deployment of all materials to the sites and by the full-scale testing which minimizes the risk of rework.

A re-bake of major elements of the vacuum system (not including the beam tube) with the entire detector components installed is included in the risk and contingency plan for Advanced LIGO. Initial LIGO experience will guide our decision to execute or omit this bake.

The schedule (top level) is shown in Figure 26.

103 LIGO M030023-00M

Figure 26 Top Level Advanced LIGO installation Schedule64

64 Based on the Advanced LIGO project schedule, LIGO M020121-D

104 LIGO M030023-00M

18. Project Management (PM)

Overview

The Advanced LIGO Project Office will be organized in the same way as for initial LIGO construction65. The principal difference is that some functions will be supported by the LIGO Laboratory operations budget (WBS 2.0). Only the incremental and specific Advanced LIGO tasks will be supported from this element of the Advanced LIGO WBS.

Functional Requirements

Advanced LIGO Project Management must provide a means of managing project performance with an earned value system, and maintaining control of the Advanced LIGO configuration and baseline. It must provide project reporting, manage project procurements, safety, quality assurance, provide definition and support of the technical system configuration and interfaces, and support general computing, document control and information systems.

Concept/Options

The management concept is the same as the initial LIGO technique and this will be described in an Advanced LIGO Project Management Plan. The Advanced LIGO Project Management Plan will be substantially similar to the Plan used during initial LIGO construction.

R&D Status/Development Issues

There are no development issues or R&D for this WBS element.

Work Plan

An Advanced LIGO Project Office will be organized and will manage the presently ongoing pre- construction R&D as well as the fabrication and construction phase proposed here. It will be part of the LIGO Laboratory. It will rely on some services provided by the LIGO Laboratory Directorate and Business Group and will contain the incremental tasks required by Advanced LIGO construction.

65 LIGO Project Management Plan, LIGO M950001-C-M.

105 LIGO M030023-00M

19. Schedule

Advanced R&D Summary Schedule

The Advanced R&D Summary Schedule is maintained by the Laboratory66. The Advanced LIGO construction project Summary Schedule below has been coordinated with that schedule.

Advanced LIGO Summary Schedule

Milestones for potentially critical path Advanced LIGO activities are listed in Table 13. These milestones are coordinated with the development schedule.

66 Advanced R&D Schedule, LIGO M020121

106 LIGO M030023-00M

Table 13 Advanced LIGO Construction/Installation Summary Milestones

Milestone Date at End of Quarter Per Calendar Year NSF Early Funding for Core Optics Available 1 Apr 2004 NSF Funding for Advanced LIGO Construction Available 1 Apr 2005 Vacuum Equipment Contract Placed 26 May 2005 Vacuum Equipment Ready to Install 10 Nov 2006 Clean Rooms Contract Placed 1 Apr 2005 Clean Rooms Available for Staging Areas 2 Feb 2006 Clean Rooms Available for Vacuum Equipment Areas 8 Mar 2007 Seismic Isolation Final Design Review 17 Nov 2004 Seismic Isolation Assembly Started 11 Nov 2005 Seismic Isolation Ready for Installation 17 Aug 2006 Suspension Subsystem Final Design Review 8 Mar 2006 Suspension Subsystem Assembly Started 24 Aug 2006 Suspension Subsystem ready for Installation 2 May 2007 Pre-stabilized Laser Final Design Review 17 Aug 2005 Pre-stabilized Laser ready for Installation 2 Nov 2006 Core Optics Components Final Design Review 27 Apr 2004 Core Optics Components First Articles Available for Suspension 2 Mar 2006 Interferometer Sensing and Control Final Design Review 16 July 2005 Installation begins at Livingston 8 Mar 2007 Installation begins at Hanford 15 Nov 2007 Commissioning begins at Livingston 21 Sep 2007 Commissioning begins at Hanford 29 May 2008 Livingston Operational 4 Mar 2009 Hanford Operational 6 Jan 2010 Milestone Date at End of Quarter Per Calendar Year NSF Early Funding for Core Optics Available 1 Apr 2004 NSF Funding for Advanced LIGO Construction Available 1 Apr 2005 Vacuum Equipment Contract Placed 26 May 2005 Vacuum Equipment Ready to Install 10 Nov 2006 Clean Rooms Contract Placed 1 Apr 2005 Clean Rooms Available for Staging Areas 2 Feb 2006 Clean Rooms Available for Vacuum Equipment Areas 8 Mar 2007 Seismic Isolation Final Design Review 17 Nov 2004 Seismic Isolation Assembly Started 11 Nov 2005 Seismic Isolation Ready for Installation 17 Aug 2006 Suspension Subsystem Final Design Review 8 Mar 2006 Suspension Subsystem Assembly Started 24 Aug 2006 Suspension Subsystem ready for Installation 2 May 2007 Pre-stabilized Laser Final Design Review 17 Aug 2005 Pre-stabilized Laser ready for Installation 2 Nov 2006 Core Optics Components Final Design Review 27 Apr 2004 Core Optics Components First Articles Available for Suspension 2 Mar 2006

107 LIGO M030023-00M

Interferometer Sensing and Control Final Design Review 16 July 2005 Installation begins at Livingston 8 Mar 2007 Installation begins at Hanford 15 Nov 2007 Commissioning begins at Livingston 21 Sep 2007 Commissioning begins at Hanford 29 May 2008 Livingston Operational 4 Mar 2009 Hanford Operational 6 Jan 2010

Relationship to Laboratory initial LIGO and Operations Schedule

Initial LIGO scientific operations will continue during 2007. Through 2006, LIGO Laboratory staff supported under the existing Cooperative Agreement will be carrying out the portions of the LSC R&D program related to Advanced LIGO. Advanced LIGO construction funds will support incremental staff required to carry out Advanced LIGO design, fabrication and assembly.

Following shutdown of the initial LIGO detector systems, a significant portion of the LIGO Laboratory staff becomes available to support Advanced LIGO installation and commissioning. In addition, incremental contractor staff will be added to support installation. These contractors are budgeted in the Advanced LIGO construction estimate.

Participating LSC members from outside the LIGO Laboratory are expected to support installation and commissioning of the LIGO systems. This participation will be managed as described elsewhere in this document.

108 LIGO M030023-00M

20. Cost Estimate

Methodology for this estimate

The cost estimate developed for this proposal was performed at the lowest feasible level, given the present level of development in the WBS, in a bottom-up manner. Most subsystems have been costed at a level of detail comparable to initial LIGO; several have not achieved the maturity in R&D to allow this level of detail, but carry contingency appropriate to the basis. The techniques used were the same methods used to estimate initial LIGO construction costs, though our cost experience in initial LIGO substantially improved the input knowledge base for the new estimate. Contingency was estimated using the formal graded approach to assessing technical, cost and schedule risk that was used in initial LIGO.

Estimate summary table by WBS

In FY XXXX US$ (non-escalated), we have made a cost estimate for the Advanced LIGO reference design. By subsystem, these estimates are summarized in Table 14.

Table 14 Advanced LIGO Cost Estimate Summary

WBS Subsystem Estimate (FY 2003 K$) 4.1 Facility Modifications (FAC) 4.2 Seismic Isolation Subsystem (SEI) 4.3 Suspension Subsystem (SUS) 4.4 Prestabilized Laser Subsystem (PSL) 4.5 Input Optics Subsystem (IO) 4.6 Core Optics Components (COC) 4.7 Auxiliary Optics Subsystem (AOS) 4.8 Interferometer Sensing and Controls Subsystem (ISC) 4.9 Data Acquisition and Diagnostics Subsystem (DAQ) 4.10 Support Equipment (SUP) 4.12 Data Analysis and Computing (COMP) 4.13 Installation and Commissioning (INS) 4.14 Project Management (PM) 4.0 Advanced LIGO Construction and Installation Total

This estimate is based on the reference design scope that has been chosen to include the preferred options in most choices where alternates exist. These include the choice to upgrade all three interferometers, to increase the arm length of the short initial LIGO interferometer, and to optimize performance for the significant technical options.

The costs in Table 14 do not include the R&D, and the technical and administrative support, already proposed in the existing Cooperative Agreement.

The GEO Project has proposed to provide a capital investment in this construction project. The UK proposal is for approximately $11.5 million42,67. They propose to apply these resources to providing the suspension subsystem, including suspension assemblies, their controls, and installation and commissioning. This is a particularly appropriate contribution to Advanced LIGO

67 Private communication, J. Hough, 8 January 2003

109 LIGO M030023-00M as the suspension subsystem is based upon the GEO Project implementation for the GEO 600 interferometer The German proposal is for the design and fabrication of the pre-stabilized laser (PSL) subsystem. This includes the power laser, the reference and pre-mode cleaner cavities, and the control systems for the pre-stabilized laser, and covers complete PSL units for the subsystem and system testing as well as PSL units for the observatories. The German GEO group has produced the laser for GEO-600 and has a great deal of experience in this domain. The amount of the contribution is expected to be approximately $11.5 million68

With the GEO capital contribution, the requested US Advanced LIGO costs are $ XXXXX K in FY 2000 $. Escalating this sum to the approximate mid-point of Advanced LIGO construction (2004), using the average inflation rate quoted by the US Department of Labor for the last 6 years (2.4%), yields a total request to the NSF of $ XXXXX K.

Should the GEO capital contribution not materialize in full, the Advanced LIGO implementation will be de-scoped to control the request to assure that the final requested funding is less than or equal to the estimate above.

Cost Drivers

Significant cost drivers in the Advanced LIGO estimate include:

• Upgrading of three interferometers • Rapid and closely sequential assembly and installation • Use of isolation systems with multiple actively controlled degrees of freedom • Use of multiple pendulum suspensions with additional stages and active controls • Stringent isolation requirements for smaller optics • Higher power lasers requiring expensive laser diodes and thermal control measures • Large core optics of ether sapphire or fused silica (comparable cost) • High number of control loops • High channel count for diagnostic channels • Increased detector sensitivity and bandwidth • Greater data storage needs • Greater communications bandwidth needs

Risk Areas and Contingency

Contingency has been estimated for each subsystem based upon top-level estimates by subsystem. Of the total FY 2000 $ estimate above, contingency funds have been estimated to be $ XXXXX K. The estimate is substantially based upon well known unit costs. Great conservatism has been used in carrying out the estimate, and most subsystems have potential for de-scoping. The combination of established unit costs and labor rates, and the large scope contingency support this estimate. If decisions are made to reduce scope, funds will be added to the contingency pool to offset the scope contingency.

Funding Profile

A working funding profile has been calculated which enables the planned schedule. We note that long-lead-time procurements such as the purchase of vacuum equipment components, and purchase of large optics substrates, will define early funding needs.

68 Private communication, K. Danzmann, 29 January 2003

110 LIGO M030023-00M

21. Responsibilities/Resources/Staffing

Method of Organizing Non-Laboratory Participation (LSC, MOUs, Attachments, Subcontracts)

As discussed in the section on the LIGO Laboratory Role and Responsibilities and the LIGO Scientific Collaboration Role and Responsibilities, the LIGO Laboratory will manage the execution of the Advanced LIGO Project. Non-Laboratory participants will be involved in the construction through written Memoranda of Understanding (MOU) and specific Attachments defining resources, responsibilities, deliverables and milestones. Where appropriate, activities will be supported by subcontracts placed by the LIGO Laboratory.

Subsystems and Institutional Roles

Institutional roles in the design and fabrication of subsystems will be -documented in the Advanced LIGO Project Management Plan, and in associated MOU’s and Attachments. The present state is outlined below.

GEO Participation

The GEO Project is operating a 600-meter interferometer in Germany with several advanced technologies. This instrument employs signal recycling, though in a delay line arm configuration, and multiple pendulum suspensions of advanced design. They are proposing to collaborate with the LIGO Laboratory in the construction and exploitation of Advanced LIGO. The GEO groups are members of the LSC and are participants in the LSC research and development program leading to Advanced LIGO.

GEO proposes to participate in Advanced LIGO suspensions and sapphire core optics, in the development of the signal recycling, and in the pre-stabilized laser subsystem for Advanced LIGO.

For the suspension subsystem, GEO proposes the following roles:

• GEO would lead the design and take part in the prototyping of the multiple pendulum suspensions with silica and sapphire bottom stages for the Advanced LIGO system. This activity would be carried out under the advanced R&D phase of the program • After this prototyping, GEO would participate in testing in the MIT LASTI system. This activity would be carried out under the advanced R&D phase of the program and would take place prior to construction of the first article suspension. This subsequent construction would not be the responsibility of the GEO group. • The GEO group proposes to have joint responsibility with the LIGO Laboratory for the installation and shakedown of the suspension systems. • Subject to funding agency approval, GEO would support the funding for construction and installation of the Advanced LIGO suspensions and controls and would supply a number of the sapphire test mass substrates.

For the signal-recycling task, GEO proposes the following roles:

• GEO would take a leading part in the research and development of signal recycling system for Advanced LIGO. This activity would be carried out under the advanced R&D phase of the program. • GEO proposes to have joint responsibility with the LIGO Laboratory for installation and shakedown of the signal recycled Advanced LIGO interferometers.

111 LIGO M030023-00M

For the pre-stabilized laser subsystem, GEO proposes the following roles:

• GEO would take a leading part in the identification of the approach to the high-power laser head, and consequently the integration of the selected head with the stabilization system. This activity would be carried out under the advanced R&D phase of the program. • Subject to funding agency approval, GEO would support the funding for construction and installation of the Advanced LIGO pre-stabilized lasers • GEO proposes to have joint responsibility with the LIGO Laboratory for installation and shakedown of the pre-stabilized laser subsystems.

GEO is making a proposal for a capital contribution to Advanced LIGO. They are at the final stages of approval for a proposal to the UK Particle Physics and Astronomy Research Council for a large part of the suspension subsystem and for part of the core optics. A companion proposal for provision of the laser system is about to be submitted to the relevant German funding authority. With approval of these initiatives by the respective funding agencies, and agreements contained in MOUs and specific Attachments, the GEO groups will become partners in the leadership and execution of the Advanced LIGO project.

ACIGA Participation

The ACIGA Consortium is pursuing research in a broad range of activities relating to interferometric gravitational wave detection. They have a number of laboratories, including the Gingin facility allowing interferometric tests over an 80m baseline. They are proposing to collaborate with the LIGO Laboratory in the construction and exploitation of Advanced LIGO. The ACIGA groups are members of the LSC and are participants in the LSC research and development program leading to Advanced LIGO.

ACIGA proposes to participate in the Advanced LIGO Thermal Compensation effort and to investigate the addition of a variable signal-recycling mirror to the Advanced LIGO baseline. Discussions are underway to refine the proposal, with the objective of establishing an MOU and attachments relevant to the contribution.

112