Stockpile Stewardshipquarterly

DOE/NA-0024

Office of Research, Development, Test, and Evaluation Stockpile Stewardship Quarterly

VOLUME 4 | NUMBER 3 | SEPTEMBER 2014

essage from the Assistant Deputy Administrator for Research, M Development, Test, and Evaluation, Dr. Kathleen Alexander ince the last issue of the Stockpile Stewardship Quarterly (SSQ), I have Sattended several conferences where I met researchers that represent the pipeline for staffing future Research, Development, Test, and Evaluation (RDT&E) activities. I attended the Computational Science Graduate Fellowship Annual Program Review and the American Nuclear Society’s Plutonium Futures—The Science conference. It was satisfying to see the 2014 Computational Science Graduate Fellowship Annual Program Review, July 14-17, 2014. enthusiasm of the young researchers. Funding Opportunity Announcements, such as the one for the Stewardship the NIF experiments. These experiments planned. You will read about them Science Academic Alliances program have helped weapon scientists to in upcoming issues of the SSQ. If you found at the end of this issue, allow have suggestions for future articles or us to attract the best and brightest performance simulations and reduce comments about the newsletter, please researchers of all ages. uncertaintiesimprove the fidelity in weapon of nuclear assessments. weapon contact Terri Stone at terri.stone@nnsa. doe.gov. I have also spent considerable time The article by Beiersdorfer et al. focuses interacting with stockpile stakeholders on a collaboration between the Atomic Weapons Establishment (AWE) in critical role of RDT&E in stockpile the United Kingdom and Lawrence stewardship.and refining theThese message SSQs areabout an the Livermore National Laboratory using important means to communicate our AWE’s Orion laser. Plans are presented accomplishments with a broad audience. to explore new density and temperature Inside regimes. The article by Hagen et al. 2 Research and Development of This issue of the SSQ highlights the describes the dense plasma focus Secondary Assessment Technologies: subprogram Secondary Assessment (DPF), which produces a nearly mono- A Program Second to None! Technologies (SAT) and associated code energetic neutron spectrum in short validation experiments. The opening 5 National Ignition Facility Experiments in bursts. This is useful for measuring Support of the Stockpile Stewardship article by Kiess et al. provides a high Program level description of SAT activities at by Abbas Nikroo provides a detailed 8 Shining Light on Opacity each of the weapon laboratories and discussionneutron cross-sections. of what is involved The final in creatingarticle 10 Pulsed Neutron Capabilities Developed the Nevada National Security Site. The the complicated targets for the SAT second article by Wan et al. summarizes for Experiments at Nevada National Security Site National Ignition Facility (NIF) fusion experiments. validation experiments supporting SAT. subprogram and inertial confinement 13 General Atomics’ Target Fabrication Experiments at the Omega Laser Facility As FY 2014 concludes, I am proud of Support for NNSA’s Secondary at the University of Rochester and the Z our accomplishments and productivity. Assessment Technology Experiments machine at Sandia National Laboratories I am also looking to the future and on NNSA’s High Energy Density Facilities have laid the groundwork for many of am excited about the efforts we have 16 In Memorium: Heino Nitsche

Comments The Stockpile Stewardship Quarterly is produced by the NNSA Office of Research, Development, Test, and Evaluation. Questions and comments regarding this publication should be directed to Terri Stone at [email protected]. | Technical Editor: Dr. Joseph Kindel | Publication Editor: Millicent Mischo 2

Research and Development of Secondary Assessment Technologies: A Program Secondary to None! by Thomas E. Kiess (National Nuclear Security Administration), Kimberly C.N. Scott (Los Alamos National Laboratory), Ivan J. Otero and Christopher Werner (Lawrence Livermore National Laboratory), Gregory Rochau (Sandia National Laboratories), and Steven Goldstein (National Security Technologies, LLC)

Introduction The Secondary Assessment Technologies program within the and Development’s Science Campaign Office of Research of the performance of a secondary improves the scientific understanding component of a nuclear weapon. Researchers perform refined analyses of legacy nuclear weapons test data, newprobe experiments—especially issues of interest by developing those in physics models, and validate them with regions of high density, temperature, and pressure using the National Ignition Facility (NIF) at the Lawrence Livermore National Laboratory (LLNL), the Omega Laser Facility at the University of Rochester Laboratory for Laser Energetics, and the Z Machine at Sandia interestsNational Laboratoriesand examples (SNL). of active This research overview article identifies program Figure 3-2 of the SSMP

Theactivities. Relevance of Secondary Figure 1. identifies Secondary Physics as a strand in the PCF. Assessment Technologies to NNSA’s Stockpile Stewardship Mission Extension Programs (LEPs), the charged particles, neutral particles, and to advance science-based capabilities Annual Assessment, Significant radiation in a wide range of energies. forThis assessing program’s and enduring improving interest the is Finding Investigation resolutions, Various physical effects control and/or certifications); and dynamics, radiation transport, other • Conducts premier science, as part of forms of energy transfer, behaviors in Nation’s understanding of secondary The theFY 2015Nation’s Stockpile deterrent Stewardship and capability. the plasma, and output signals. This performance. The program accomplishes 2 regime is a challenge to study and this by sponsoring relevant research, interests in its Predictive Capability probe meaningfully. and Management Plan identifies these conducted mainly at NNSA laboratories In the past, diagnostics of legacy nuclear (Los Alamos National Laboratory tests provided information used to (LANL), LLNL, and SNL) and the Framework (PCF) in the Secondary Physics “strand,” which is the program’s modelscalibrate contain weapons a representation codes—computer of Nevada National Security Site (NNSS), programs whose constituent data and which is operated by National Security focus (see Figure 1). Along the strand, program interests are identified as three Technologies, LLC (NSTec). Such research secondary performance. Insight into achieves the followingphenomenological outcomes: model explicit high-level “pegposts” in the calibrations with science-based topics of secondary reuse, secondary opportunities to improve understanding • modelsReplaces validated by experimental performance, and full system weapon physicscomes from contained secondary within designers’ them and use how of outputs. To accomplish significant gains these codes, and their knowledge of the performance goal in each of those pegposts, the program Departmentdata—in direct of Energysupport Strategic of a Plan conducts research typically spanning it is treated. Some legacy models lack full 2014-20181; of the U.S. years to provide technical outcomes that connectivity to all underlying physics—in such models, some detailed phenomena Offers advances that increase Technicalserve as constituent Thrusts buildingof Sponsored blocks. are treated in simplified terms. the range of technical options Research from targeted experiments designed to • for stewardship of the evolving What is the physical environment Improved models and/or data come stockpile; relevant to secondary design and the environmental conditions in the investigate specific effects. At present, reactions take place to create a hot with the right types of experiments at • Contributes to other stockpile denseperformance? plasma Inreplete general, with nuclear energetic facilitiesregimes ofcapable interest of canattaining be studied some of the stewardship activities (e.g., secondary-related issues in Life Volume 4 | Number 3 | September 2014 Stockpile Stewardship Quarterly 3 relevant conditions. Such experiments sponsors, such as the NNSA Nuclear (1) improving the fundamental data that calibrate new physics models of Survivability program and agencies feeds into the performance simulations, phenomena selected and controlled within the U.S. Department of Defense. (2) developing experimental platforms for detailed study. Relating these new at HED facilities to explore and validate physics models to those within legacy All of this research is challenging to the modeling of the physical processes weapons codes provides a way to conduct. Experimental work uses relevant to secondary modeling, and specialized facilities that are able (3) validating the integrated simulation to create states of matter never capabilities by simulating relevant improveMuch of thisscientific research understanding. is high energy before achievable in the laboratory underground tests (UGTs). For the density (HED) physics— exploring and diagnostics that are capable of fundamental data, sensitivity studies the behaviors of matter at extreme measuring critical aspects of HED identify what uncertainties in the data pressures, densities, and temperatures, matter with unprecedented precision. most limit the predictive capability. As an including the study of burning plasma Research teams at LANL, LLNL, SNL, and example, the uncertainty in the neutron containing thermo-nuclear fuel. NSTec make important contributions as capture cross section of certain unstable Constituent technical issues/topics illustrated in the examples below. isotopes dominates the uncertainty in include the following: Research at LANL the interpretation of some UGT data. It is well known that the neutron capture Material Properties – equations of The LANL High Energy Density state, and strength/damage/failure ReShock/Shear experiments study • for various elements in extreme to compute accurately, and given the extreme hydrodynamic processes on cross sections are notoriously difficult conditions of elevated temperature, short lifetimes of isotopes involved, it is the NIF and Omega laser facilities. The impossible to measure the cross section pressure, and density; experiments are built with different Radiation Transport – including the content and geometries depending team has used an indirect measurement opacities of materials to x-rays of on what hydrodynamic phenomena usingdirectly. the For surrogate the first reaction time, a research method4 • various energies; they are used to study. In all cases, the to infer a neutron capture cross Plasma hydrodynamics – energy millimeter-scale laser-driven target (see section. The team used yttrium in the exchanges among the plasma Figure 2, left) is irradiated on both the demonstration because it has a relatively • constituents, non-local equilibrium top and bottom, driving strong shocks simple nuclear structure, to infer the processes, particle transport (e.g., into the cylindrical tube body. In the cross section for the reaction: charged particle behaviors, to 87Y 88 γ include break-up processes and shocks, separated by a metal plate when + n -> Y + kinetic effects); theyshear are experiment launched configuration,into the tube, passthe Experimentally, the team created the each other by at the tube center. This 88 Thermonuclear burn physics – fusion same compound nucleus ( Y in an creates an intense velocity difference reactions where light atoms combine excited state) as the capture reaction, on each side of the plate, allowing 89 • to form heavier ions plus energy and by bombarding Y with a proton and researchers to study the Kelvin- the effects that they cause; and observing the emitted deuteron: Helmholtz shear instability in high- 89Y + p -> 88Y + d Dense nuclear energetic three- Mach-number, high-density settings. dimensional (3D) radiation/ burn The Kelvin-Helmholtz instability occurs They measured the emerging gamma • hydrodynamics–putting it all in everyday life when wind blows over rays as the excited 88Y decays to its together and attendant complexities. water with the resultant unstable water ground state. These data and a detailed waves. Here, the instability leads to understanding of the nuclear structure Other research is conducted in 88 precision experimental measurements mixing and the initially smooth plate is of Y enable a calculation of the of nuclear cross sections—to driven into a rough, reduce uncertainties that matter in irregular shape (see understanding what reactions take Figure 2, right). The place (e.g., those induced by energetic neutrons) and to what degree. from the left of the tubeflow speedto the differenceright is Still other research is in Latetime in excess of 100 km/ Outputs & Effects—which includes sec.3 The experiments calculations of radiation outputs (e.g., are providing critical validation data for spectra) as functions of space, time, and the use of weapons energy.neutron These fluences outputs and x-ray/gamma-ray are important program codes in to assess how a weapon discharge will evolving stockpile interact with the environment and, scenarios. subsequently, the nuclear and non- nuclear components of other weapon Research at LLNL systems in the local vicinity. This LLNL researchers are Figure 2. NIF Shear shot N140117 target (left) and radiograph program work is complementary to aggressively pursuing (right) showing the Kelvin-Helmholtz instability driven evolution of the initially smooth target interface. related work of other U.S. Government three major objectives:

Office of Research, Development, Test, and Evaluation Volume 4 | Number 3 | September 2014 4 capture cross section as a function the associated spectral features from predictive capability, and modernization of neutron energy (see Figure 3). the myriad of excited states that exist studies. Core capabilities are in design, The experimentally informed cross at these extreme conditions.5-6 In the engineering, “ruggedization,” and section is within the uncertainty band case of x-ray source development, other development of HED diagnostics of the previously modeled theoretical z-pinch implosions on the Z facility instrumentation and sensor systems evaluation. produce the world’s brightest laboratory that cover a wide spectral range from x-ray sources in the 1-10 keV spectral radio frequency to energetic photons Research at SNL range.7-9 These z-pinches are typically to ionizing radiation, and in providing Secondary assessment activities at formed by cylindrical arrays of wires standards-based calibrations of that are imploded by a current of over detectors, sensors, and components in questions about the way radiation 20 million amps. The high kinetic these diagnostics systems to support transportsSNL are focused through on andaddressing interacts specific experiments (see Figure 5). For example, with matter at extreme temperatures, converted into K-shell x-ray energy as pressures, and/or radiation intensities. theenergy z-pinch of these stagnates implosions at the is axis. efficiently Recent The principle issues under investigation work has extended the spectral range tailoredNSTec develops to meet neutronHED experimental time-of-flight include (1) the measurement of of these sources to photon energies measurementdetection systems requirements. with specifications opacity in hot, dense plasmas, (2) >13 keV utilizing jets of krypton gas as the progenitor for the z-pinch (see NSTec operates calibration facilities in complex geometries, and (3) the Figure 4). Benchmarked models of located at LLNL and SNL that include developmentthe characterization of intense of radiation x-ray sources flow for Manson, Henke, and high-energy x-ray applications in radiation effects sciences. radiation-hydrodynamic simulations to laboratories; the Long-Pulse Laser, Each of these issues is addressed designthe supersonic z-pinches Kr at gas simulated flow initiate implosion 3D Short-Pulse Laser and Enhanced Short through experiments on the Z facility velocities exceeding 1,000 kilometers/ Pulse Laser laboratories; the Optical at SNL that are designed, executed, second that are proven to produce >5 Component Calibration Laboratory; and analyzed in close collaboration kJ of Kr K-shell radiation at >13 keV. and the Electronic Systems Calibration with LANL, LLNL, and academia. In the These bright x-ray sources provide a Laboratory. A Manson source and case of opacity studies, Z experiments broad range of spectral energies that Picoprobe station continue to anchor the measure detailed frequency-dependent enable radiation effects testing at microchannel plate (MCP) Assembly and opacity with a precision of 10% at Characterization Laboratory at SNL and electron temperatures and densities up laboratory. provide the necessary characterization to 200 eV and 4E22 cm-3. This allows for fluences previously unattainable in the and life-cycle maintenance of x-ray the study of bound-bound and bound- Research by NSTec framing cameras for imaging and free opacities, including the shape of NSTec, the M&O contractor for the NNSS spectroscopic diagnostics. Other ongoing and other facility locations, conducts activities include developing MCP and high-hazard experimentation supporting 10 nuclear weapon stockpile relevant streak cameras and spectrometers, and participatingphosphor coating in the capability, design of fielding advanced 1

0.1 work in assessment, certification,

0.01

0.001 Cross Section (barns) Cross

0.0001 10

1

0.1

0.01

0.001 Cross Section (barns) Cross

0.0001 0.001 0.01 0.1 1 10

En (MEV) Figure 3. Comparison of the surrogate evaluation of the neutron capture cross sections for yttrium-87 from the ground state (gs) (top), or the isomer state (bottom). The gray band represents the estimated uncertainty in the theoretical cross section, and the dotted lines Figure 4. Supersonic gas puff nozzle for a z-pinch experiment on the Z facility that demark the estimated uncertainty in the produces >5 kJ of Kr K-shell x-rays at >13 keV photon energy. Three-dimensional surrogate evaluation. simulations are used to optimize the z-pinch design for maximum x-ray yield.

Volume 4 | Number 3 | September 2014 Stockpile Stewardship Quarterly 5

for critical calibrations of components. because it pushes the limits of the state- With the scheduled closure of NSLS by Sample – Poly aerogel 28% the end of FY 2014, and the decision methods that are used. Accompanying absorbtion to site a replacement x-ray calibration articlesof-the-art within in the this scientific issue of and the technical Stockpile station at the Stanford Synchrotron Stewardship Quarterly describe several Fracture in sample Radiation Lightsource (SSRL), NSTec ongoing research activities in greater No Fiber will continue to lead the tri-lab team depth. absorbtion from sample in collaborating with SSRL to develop holder the required synchrotron-based x-ray References beamline endstations. This development 1U.S. Department of Energy Strategic Plan effort is underway, scheduled to be 2014-2018, March 2014, DOE/CF-0067. completed by the end of 2015 and to 2Fiscal Year 2015 Stockpile Stewardship Figure 5. Example of Recent NSTec be operational by mid-FY 2016 after and Management Plan: Report to Diagnostic Development. On the commissioning. NSTec Manson X-Ray Source, scientists Congress, U.S. Department of Energy, Summary DOE/NA-0021, April 2014. strength target aerogel on a newly 3Doss et al., Phys. Plasmas 20, 122704, The Secondary Assessment Technologies collecteddeveloped the contact first images radiography of a materials end 2013. station. These foams are used in 4 materials strength shots at NIF and are that probes challenging technical J. Escher, J. Burke, F.S. Dietrich, N.D. critical to experimental performance. If issuesprogram using sponsors specialized scientific facilities research and Scielzo, I.J. Thompson, and W. Younes, the capability meets requirements, the instrumentation. Research outcomes are Reviews of Modern Phys. 84, 353, 2012. materials strength target team will use designed to prepare design laboratories 5J.E. Bailey, G.A. Rochau, C.A. Iglesias et the contact radiography station for foam al., Phys. Rev. Lett. 99, 265002, 2007. characterization on future materials strength and high-Z shots at NIF. issues, and stockpile assessment 6J.E. Bailey, G.A. Rochau, R.C. Mancini et challenges.for future LEP Advances options, improve recertification the al., Phys. Plasmas 16, 58101, 2009. science basis for current stockpile 7C.A. Coverdale, B. Jones et al., High assessment and provide the foundational diagnostics such as a compact recoil Energy Dens. Phys. 6, 143, 2010. understanding needed to assess new spectrometer and Thomson parabola. 8 stockpile options. This research also B. Jones, C. Deeney, C.A. Coverdale et At the Brookhaven National Laboratory’s maintains the vitality of the workforce al., J. Quant. Spectrosc. Radiat. Transfer National Synchrotron Light Source and trains the next generation of 99, 341, 2006. (NSLS), NSTec leads the team composed theoretical, computational, and 9D.J. Ampleford, B. Jones, C.A. Jennings of LANL, LLNL, and SNL to use x-ray experimental physicists. Their mission- et al., Phys. Plasmas 21, 056708, energies that range from 50 eV to 25 keV 2014. ●

critical research has an exciting flavor

National Ignition Facility Experiments in Support of the Stockpile Stewardship Program by Alan Wan (Lawrence Livermore National Laboratory), Kimberly Scott (Los Alamos National Laboratory), and the Los Alamos National Laboratory and Lawrence Livermore National Laboratory High Energy Density Teams

Experiments on the National Ignition The improved numerical simulation the University of Rochester Laboratory Facility (NIF) at Lawrence Livermore codes, which will be benchmarked and for Laser Energetics and Z at Sandia National Laboratory (LLNL) contribute to validated against underground nuclear National Laboratories, validated a the enduring U.S. nuclear deterrent in the test results and experiments at the NIF, physics-based theory and simulation absence of additional nuclear testing by: will enable nuclear weapon scientists to capability that was a major factor leading to the resolution of a long- Elucidating key weapons performance simulations and reduce standing anomaly left unanswered when performance issues left unanswered uncertaintiesimprove the fidelity in U.S. ofand nuclear foreign weapon nuclear underground testing was suspended. • when testing stopped; weapon assessments and U.S. warhead Data obtained from NIF showed that Validating physics models the theory and simulation capabilities incorporated in numerical capabilities to provide data needed by developed to remove this anomaly • simulation design codes of the thecertifications. SSP because NIF of is its unique ability in to its produce were correct. The elimination of this Advanced Simulation and Computing extreme energy density conditions over program, upon which the Stockpile reasonably large volumes combined with accomplishment for the SSP; eliminating Stewardship Program (SSP) relies; high-resolution diagnostics. oneanomaly of the represents key technical a significant reasons for having to potentially return to Maintaining aspects of test NIF has already provided critical data underground testing and enabling readiness; and to the SSP. Results from a series of production decisions in support of • Recruiting, training, and retaining non-ignition experiments on NIF, and stockpile sustainment. The experimental weapons program personnel. precursor experiments on Omega at • campaign (defined as a series of shots/ Office of Research, Development, Test, and Evaluation Volume 4 | Number 3 | September 2014 6 experiments to achieve a common high strain rate. Experiments objective) on NIF was preceded by include the measurements of many months of platform development, diffraction data to discern the utilizing experimental shot time on phase structure and strength Omega and Z to test diagnostics, targets, data to bound the constitutive and data acquisition and reduction. properties. Figures 1 (strength) The effort on Omega and Z enabled and 2 (phase) show the this experimental platform to be implemented on NIF very rapidly and experimental campaigns. the experimental series completed to configurations of these two support the closure of the effort. Scaled experiments on NIF are being used to address complex The acquisition of weapon-physics- hydrodynamic phenomena relevant data in the high energy density important to predicting (HED) physics regime to validate these nuclear weapon performance. Figure 1. The material strength experimental physics-based models is essential to the Experiments are “scaled” campaign measures the deformation of solids under development of predictive capabilities when physical quantities for high pressure and high rate. for stockpile applications. Data the experiment—size, generated from both ignition-relevant density, and pressure—are and non-ignition HED experiments selected in a coordinated are categorized into four main topics: manner so that the nuclear, thermonuclear, radiation, and hydrodynamic behavior is output and effects. the same as the weapons- physics problem, albeit Nuclear on a different scale—just The nuclear area focuses on the as scaled airplanes in physics during the implosion phase wind tunnels stand in of the system. During the implosion for yet-to-be-built, full- phase, the components are driven at scale airplanes. They high-pressure and high-rate, and are help to “set or eliminate compressed hydrodynamically. The calibration parameters” most important physics areas are the and provide a means for material properties at these conditions, validating physics codes the implosion hydrodynamics, and the used to examine issues nuclear properties (such as nuclear during the nuclear phase of Figure 2. The material diffraction (material phase) cross sections) at the pressure and weapons functioning. They are experimental campaign measures the diffracted temperature conditions similar to also vital for development of line pattern, which is a unique signature of material those at the centers of giant planets computational models, helping phases at various pressures and temperatures. and stars. Key HED efforts in this nuclear weapon scientists area are the measurement of relevant develop and choose alternative models into hot plasma and are subject to material properties at the high-pressure and computational methods to solve strong dynamic interactions. The and high-rate condition, the study of the stockpile problem of concern. dynamic interactions and symmetry hydrodynamics of imploding systems, Scaled experiments have begun on and the measurement of key nuclear the NIF and Figure 3 provides some burn performance. Key HED efforts of the key NIF capabilities required to focushave impacton the onstudy the ofefficiency burning ofplasma support this experiment. performance in the presence of mix, physics cross sections, such as fission burn, and symmetry issues. andAccurate fission data fragments. about material properties With recent results that delivered near or at thermonuclear conditions is neutron yield in the high 1015 range, Currently, even the most powerful needed to improve the physics models in we have started experimental designs computers are incapable of calculating weapon performance simulation codes. high-speed turbulence processes NIF experiments provide precision data on the smallest scales of interest. in high pressure (millions to billions andto utilize radiochemical the high neutron cross sections. flux to study Data As a result, most codes incorporate of atmospheres) and high temperature willnuclear enable physics us to and bound measure the nuclear key fission cross (surface of the sun to the interior sections in a regime not accessible by and turbulence. Different algorithms of massive stars) regimes that are traditional neutron sources. andsimplified models models may produce for instability different growth otherwise inaccessible in the absence of results. Hence, it is necessary to use nuclear testing. The material properties Thermonuclear experimental data to select the most In thermonuclear reactions, the system appropriate model and/or set model equation-of-state, material strength, and reaches very high temperatures and parameters. Application of simulations phasedata broadly structure. fit into Current three experiments categories: on densities, similar to those at the center extends to a wider set of problems and NIF focus on obtaining material dynamic of stars and that of a supernova. At leads to results of increasingly uncertain data at high pressure and density and at these conditions, the materials turn validity, as the problems deviate from

Volume 4 | Number 3 | September 2014 Stockpile Stewardship Quarterly 7

Figure 4. HED experiments on NIF are used to study mix at the fuel-ablator Figure 3. The complex hydrodynamics experimental campaign studies the dynamic interface and its impact in degrading evolution of system driven by imposed perturbations. implosion performance. the experimental baseline. Figure 4 displays a simulated result on the extent of mix at the fuel-ablator interface of an imploding NIF capsule with a prescribed numerical model. Figure 5 shows a planar experimental platform to study the increasing mix width due to shear instabilities. With the improvement of imploding capsule performance and robustness on NIF, we are beginning to explore the utilization of current and future capsules to study burning plasma and thermonuclear physics. Planned Figure 5. The NIF platform is used to quantify rate of instability growth and benchmark near-term applications include the the numerical model parameters. validation of code and model of capsules imposed perturbations. As the capsule govern the absorption and transmission methods and give inexact data with performancewith significant continues self-heating to improve, with it of x-rays in nuclear devices. will allow the SSP community to expand as input into the large simulations. the application of capsule yield. More Numerical modeling of radiation Opacitydifficult-to-quantify experiments uncertainties to date have been detailed applications were delivered in a transported in a nuclear weapon very important in improving opacity 90-day study report submitted in 2012 is complicated by the extremes in theory and models, but they have conditions encountered and the various been restricted to lower temperatures of Ignition 90-day Study, Alan Wan et and densities than those critical to al.,(Classified SRD Report, Appendix Lawrence to the Livermore Application be addressed. NIF provides a platform nuclear-phase weapon performance. National Laboratory, COPD-2012-0031, togeometrical conduct experiments configurations that that allows must the NIF provides the conditions required February 2012.). validation of numerical algorithms in these relevant regimes. advance models in the relevant high Radiation temperatureto obtain opacity regime. data to significantly The radiation effort focuses on the study The opacity of a material governs the of radiation transport in SSP-relevant absorption and transmission of x-rays in Output and Environment a nuclear explosive device. The opacity The output and environment efforts opacity models at relevant temperature of materials is necessary data for codes focus on the post-explosion phase where andconfigurations density conditions. and the validation Key HED efforts of that simulate the transport of radiation the nuclear weapon releases x-ray, in this area are the measurement of in weapons, a key factor in device neutron, and gammas on the intended radiation propagation in relevant performance. First-principles computer targets. In addition, the study of physics models used to calculate opacities are of weapon output and effects allows us algorithms incorporated in the design beyond the scope of today’s largest to assess the consequence of using the codesgeometries and to to obtain validate data the to radiation validate flow supercomputers. Instead, models that weapons, both intended and unintended, generate opacity data use approximate in both the near- and long-terms. Key first-principle opacity models, which Office of Research, Development, Test, and Evaluation Volume 4 | Number 3 | September 2014 8

HED efforts include developing relevant Near-term Milestones and FY 2015 sources that model weapon output Deliverables for SSP Experiments Complete the readiness to conduct and utilize these sources to study on NIF the coupling of radiation for effects Currently, LLNL and Los Alamos National • dynamic diffraction experiment at assessment and validation. Laboratory are planning to conduct more highthe first strain SSP-relevant rate and high high-Z pressure. material After the weapon as a whole has than 10 experimental campaigns in the Launch development of new functioned, the device emits its energy FY 2014-2015 timeframe across the four hydroburn HED platform on Omega into the environment through its key topics described above. The major • & NIF for the Marble campaign, output as a function of time-, energy-, near-term deliverables follow. including initial decision point on and spatial-dependent x-ray, neutron, target design feasibility. FY 2014 Complete the acquisition of shear interact with the environment (e.g., Continue to advance the low energy density, high energy thegamma atmosphere, fluxes. These space) radiation to produce fluxes a understanding of ignition science. • density, and direct numerical wide variety of effects, which have far- • Develop the high-Z material simulation data that will be used to ranging impacts on overall consequence experimental platforms at high- impact the FY 2016 Life Extension of execution, forensics, and counter- • pressure and strain rates. Program Level 1 Milestone. proliferation. NIF delivers the energetics to develop the needed platforms to Complete experimental campaign to validate the models that assess the validate mix at fuel-ablator interface experiment in complex SSP-relevant interaction of radiation with a variety • for imploding capsules at two • geometry.Start first radiation● transport of targets. convergence ratios.

Shining Light on Opacity by Peter Beiersdorfer (Lawrence Livermore National Laboratory) and David J. Hoarty (Atomic Weapons Establishment)

Commissioned just over a year ago, Opacity measurements have been centigrade while maintaining solid the Orion laser at the Atomic Weapons performed before at the HELEN laser density. Establishment (AWE) in Aldermaston, at AWE, the Nova laser at LLNL, at England (see Figure 1), has become a the Omega laser at the University The Orion facility also has 10 beams key facility for measuring the properties of Rochester Laboratory for Laser operating at a much larger pulse length. of hot, dense matter. These experiments Energetics, and at the Z facility at the These can be used to shock the target require the most advanced equipment Sandia National Laboratories.4,5 The and further increase its density. for measuring the radiation emitted Orion laser is unique in that it allows Diagnostics Are Key in a burst of x-rays lasting a few us to reach much higher densities and picoseconds, i.e., a few trillionths of a temperatures than have been achieved by In order to infer the parameters that second. The experiments are carried the other facilities. out collaboratively between scientists at matter, we measure the x-rays produced AWE and Lawrence Livermore National How does it Work? bydetermine the sample the itself.flow of These light x-raysin hot, dense Laboratory (LLNL), who have built on carry information about the density, expertise developed at the HELEN laser green light at a dot of sample material temperature, and radiative energy loss at AWE and at the Europa and Titan smallerThe Orion than laser the fires period a photon at the endbullet of of of the sample as well as on the sample’s lasers at LLNL.1,2,3 this sentence. This bullet has a duration state of ionization, i.e., the degree to of 0.5 picoseconds; it has a size less than which the electrons have been peeled six thousandths of an inch. This is more off the atoms in the sample. understanding weapon performance. than a thousand times shorter than the Energy flow is a crucial element in The ultrashort duration of the laser- laser beams produced at LLNL’s National matter interaction requires that in our weapon codes to assess the Ignition Facility. The shape of this performance,This energy flow safety, must and be reliability simulated of our measurements be carried out with ultrahigh time resolution, stressing nation’s nuclear stockpile. Incorporating ensure that all its energy hits the target measured or experimentally validated atphoton once. bullet is very precisely defined to material properties that impede or instrumentation. the leading edge of the scientific The sample material is sandwiched We use the world’s fastest cameras to improving these simulations. The between two layers of carbon in the that streak the sample’s x-ray emission experimentsfacilitate the flowat Orion of energy aim at is measuring a requisite form of plastic or diamond that prevent with sub-picosecond resolution (see it from expanding at these ultrashort Figure 3).6 These measurements are material to determine a crucial quantity time scales (see Figure 2). The result is a augmented with absolutely calibrated, calledthe flow the of opacity. x-rays through hot, dense sample heated to many million degrees time-integrating crystal spectrometers,

Volume 4 | Number 3 | September 2014 Stockpile Stewardship Quarterly 9 which provide high spectral resolution. Pin-hole imagers measure the size of the material illuminated by the laser beam.

Material Properties at the Quantum Edge The high density and temperatures in the sample bring out quantum mechanical effects that change the material properties and are challenging principles. Having precise handles on theto quantify density theoreticallyand temperature from in first our experiments, we can watch as a given atom loses its ability to hold on to its electron through a process called Figure 1. The Orion laser facility. ionization potential depression (IPD). IPD is an effect in which the atom has fewer quantum mechanical states as the developed at AWE and density is increased, thus reducing its LLNL and are also ability to keep its electrons. being benchmarked against the Orion IPD models are crucial inputs for our data. In addition ability to predict material properties. to temperature Recent experiments at the Linac and density, the Coherent Light Source (LCLS) facility sample thickness, at Stanford University have called emission duration, into question the validity of the most and emission area widely used IPD model.7 We conducted together with the experiments on the Orion facility to response function of Figure 2. Target arrangement for opacity measurements on the detectors must Orion. Two long-pulse laser beams of red light irradiate the explore IPD in the hot, dense matter backside of the target, inducing a shock wave that compresses regime not accessible by the LCLS be known to make a the sample. One short-pulse laser beam of green light measurements (see Figure 4). We meaningful comparison. irradiates the front of the target and heats the sample. The found that the standard model gives diameter of sample is two thousands of an inch, its thickness the best description of IPD in this criteria simultaneously is less than 10 millionth of an inch. The plastic or diamond regime.8 However, the predictions do isFulfilling a grand all challenge of these of not perfectly match our data, which opacity measurements. times (back) thicker than the sample. indicates that improvements in the that surrounds the sample is twenty times (front) to fifty Our initial model and new measurements on an measurements showed that Orion heated the evenOpacity finer Measurements density scale are warranted. sample more than expected so that the If all relevant parameters in the sample sample was too far have thermalized, i.e., they can be from the required LTE described by a single temperature, conditions. Achieving the sample is said to be in local higher temperatures thermodynamic equilibrium (LTE). than planned is a better Materials in LTE are much easier to model than those that are not in LTE, that temperatures because a statistical approach can be aresituation too low. than We finding have used. If the sample deviates from LTE now redesigned our by only a small amount, the absolute targets to lower the x-ray emissivity can still be compared temperature to the with LTE spectral predictions invoking desired values. an equivalent ionization temperature Figure 3. U.S.-built, time-resolved x-ray spectrometer for a particular density as given by On Orion, we have installation on Orion. scaling relations developed by Busquet.9 another knob to LTE models are a subset of the more approach near-LTE conditions: We thereby bring the statistical occupation general non-LTE models, which can use the aforementioned sample of the available quantum mechanical calculate the processes in the sample in compression to increase its density. At states to near LTE. We have now started detail without resorting to statistical to implement long-pulse compression in averages. Non-LTE models are being overwhelm radiative processes and our opacity experiments. sufficiently high densities, collisions Office of Research, Development, Test, and Evaluation Volume 4 | Number 3 | September 2014 10

The Future Engineers (SPIE) Conference Series The Orion laser 3157, 2, 1997. facility is still evolving. 2D.J. Hoarty et al., “High Temperature, Expected upgrades High Density Opacity Measurements to the facility in the Using Short Pulse Lasers,” Journal of coming year will Physics: Conf. Series 244, 012002, 2010. double the available 3C.R.D. Brown et al., “Measurements of energy of the green Electron Transport in Foils Irradiated laser light, allowing with a Picosecond Time Scale Laser us to investigate Pulse,” Physical Review Letters 106, larger samples with 185003, 2011. more homogeneous 4T.S. Perryuble et al., “Absorption conditions and to Experiments on X-Ray-Heated Mid-Z obtain more signal Constrained Samples,” Physical Review E in our time-resolved Figure 4. Comparison of ORION experimental data of 54, 5617, 1996. measurements. AWE aluminum (shown in the center panel) with two IPD model 5 is planning additional predictions (shown in the right and left panels). The density J.E. Bailey et al., “Iron-Plasma major upgrades of the increases from bottom to top (from 1.2 to 9.1 grams per cubic Transmission Measurements at centimeter) for each of the red curves. Our experimental data Temperatures Above 150 eV,” Physical year horizon that will rule out the model favored by the recent LCLS experiment. Review Letters 99, 265002, 2007. pushlaser thewithin accessible a five- Instead, the experimental data favor the predictions in the 6E. von Marley et al., “Ultra Fast X-ray leftmost panel, but the agreement is not perfect. parameter range Streak Camera for Ten Inch Manipulator to new regimes of interest to stockpile stewardship. Instruments 83, 10E106, 2012. Together, our collaboration will 7BasedO. Ciricosta Platforms,” et al., Review“Direct ofMeasurements Scientific explore new density and temperature Concurrently, our instrumentation of the Ionization Potential Depression in is evolving to match the signal a Dense Plasma,” Physical Review Letters produced by the Orion laser. We are understanding of nuclear weapons. 109, 065002, 2012. in the process of building a second regimes needed to refine our predictive 8 sub-picosecond streak camera. A References D.J. Hoarty et al., “Observations of the time-resolved pin-hole imager, a 1R.L. Shepherd et al., “Subpicosecond Effect of Ionization-Potential Depression radiation thermometer, and a focusing Time-Resolved X-ray Measurements,” in Hot Dense Plasma,” Physical Review x-ray spectrometer with very high in Applications of X Rays Generated Letters 110, 265003, 2013. spectral resolution are expected to from Lasers and Other Bright Sources, 9 join the existing suite of leading edge ed. by G.A. Kyrala and J.-C. J. Gauthier, za tion Model for Laser-created Plasmas,” diagnostics in the coming year. Society of Photo-Optical Instrumentation PhysicsM. Busquet, “Radiation-dependent of Fluids B 5, 4191, 1993. Ioni-●

Pulsed Neutron Capabilities Developed for Experiments at Nevada National Security Site by Chris Hagen, Daniel Lowe, Frank Cverna, Steve Goldstein, and David Pacheco, National Security Technologies, LLC (Nevada National Security Site)

deuterium (D) experiments but that Yields have increased over three decades research in the late 1950s, a series of was the limit. Now in 2014, with the of development effort. Operational ideasAfter theand declassification papers emerged of on fusion ways to two DPF research and development produce fusion using z-pinches. In 1965, facilities in Nevada, the U.S. Department 6,000 DPF shots have been executed J.W. Mather and a team at Los Alamos of Energy(DOE)/National Nuclear soflexibility far. This has program greatly has increased. established Over a National Laboratory (LANL) published Security Administration (NNSA) now world-class DPF performance capability results showing remarkable neutron has the highest current DPF capability within DOE/NNSA. yields from a relatively compact, low- in America and is using it to further current generator: a dense plasma several DOE missions. What is a DPF Machine and focus (DPF). Data did show that this How Does It Work? laboratory-scale device was a powerful During the period of designing sources to While DPFs were invented and optimized neutron source but, alas, the neutrons meet mission requirements and building 1 the operative were created by instability mechanisms laboratory capability, National Security plasma physics processes are yet to be rather than a bulk thermal process. Technologies, LLC (NSTec)-designed fullyover understood.five decades Theago, DPF system that Work over the next 25 years showed and -built DPFs have grown from storing produces fusion is simple in concept that these DPF devices could scale less than 100 kilojoules to having the while also being a product of a rich to about 1 x 1012 neutrons in pure capacity of storing up to 2 million joules.

combination of scientific and engineering Volume 4 | Number 3 | September 2014 Stockpile Stewardship Quarterly 11 disciplines. Shown in Figure 1 is the of a second; the Gemini DPF source. Inside a dense plasma fusion processes focus machine, light gases are heated and last for less than magnetically compressed to conditions a millionth of a similar to those inside the sun. second. Neutrons are emitted in a tiny In the sun, Z machine, National Ignition volume about the Facility (NIF), and DPF, gas atoms size and shape of a fuse to form heavier products. Fusion short piece of pencil releases energy, both in the form of lead, a cylinder high-energy particles and photons. roughly 1 mm in DPF operation is roughly analogous radius and 10 mm long. Neutrons are emitted at rates up to to the familiar stroboscopic flash used energy from a direct current power 1020 per second. sourcein a camera: (the battery) the flash to slowly charge transfers a capacitor storing this energy with the ability to Unlike nuclear Figure 1. The “Gemini” megajoule DPF source. The blue discharge it almost instantly. To cause reactors that emit assemblies are capacitor banks that store energy; the white neutrons over a coaxial cables transmit current to the central DPF tube assembly. broad range of gasthe flash,causing the it capacitors to emit a very are dischargedshort, very energies, DPF fusion through a gas-filled tube, ionizing the devices are fairly mono-energetic. This The Road to a World-Class taken. In a DPF, the physics used allows DPF Capability thebright slow flash capacitor of light discharge and the picture (many is of physics experiments, for instance, A legacy 1.5 kJ DPF source was supplied microseconds) to be converted into a characteristic is beneficial for many types measuring nuclear cross-sections. to NSTec and, with the knowledge rapid energy compression (less than Also, the DPF emits neutrons in very gained from operating it, a series 100 ns). In the Z facility and in NIF, in short bursts, allowing for fast time of sequentially larger sources were contrast, the pulsed power or laser resolution. Furthermore, DPF machines assembled and tested (see Figure 3). systems are designed to produce an are quite compact in comparison to Based on NSTec’s operation of the energy pulse of 100 ns or less. large accelerators that are used as legacy DPF source, around the year neutron sources; this makes them ideal In the Nevada DPF machines, up to 2000, LANL requested that NSTec for applications where space is at a 1 million Joules of energy is stored in design and fabricate a specialized DPF premium or where transportability is large capacitors at voltages of up to for a proposed downhole subcritical 70,000 volts, awaiting the command experiment named Unicorn at the provide a research and application to generate neutron-producing fusion. NNSS. NSTec designed and built the nicherequired. in which These the defining DPF excels characteristics as a tool to The currents create intense magnetic 133 kJ OneSys machine as the result of accomplish high quality research quickly this effort. It produced over 1010 2.45 neutrons per pulse using deuterium, and fields and the high voltage causes high subsequently over 1012 14 MeV neutrons source tube. DPF machines use many andThe efficiently.DPF machines at the Nevada National gases,electrical including fields in D the and gas-containing tritium (T). Security Site (NNSS) are producing when using DT gas mix as fuel. The insulating gas becomes ionized, 13 intense (up to 10 ) 14.1 MeV neutrons LANL subsequently requested the transforming into current-carrying per burst, and short (less than 100 ns) fabrication of a more powerful DPF plasma. The plasma is pushed to the pulses of either 2.45 or 14 MeV neutrons source that would burn DT gas and make reaction point in the tube at the end of from nuclear fusion using D or DT gases. over 1013 14.1 MeV neutrons per pulse, the anode, as shown in Figure 2. There in a single burst that is very narrow in Mather in the United States and time. Furthermore, the source is required plasma into a very small volume, making Filippov2 in the Union of Soviet Socialist itthe dense intense and magnetic hot; hence fields the compressname “dense the Republics independently discovered tunnel complex at the NNSS as part of a the process of neutron production futureto be compact experiment in order series. to fit into the U1a process is called a z-pinch. Temperatures with DPF machines. Using deuterium, andplasma pressures focus.” ofThe the final plasma compression reach both Mather and Filippov succeeded in Under development, a 350 kJ Sodium extreme conditions like those on the reaching neutron yields of greater than source has produced pulses of over 12 outer parts of stars. The DPF is not hot 10 neutrons per burst. Today, there 1013 14.1 MeV neutrons per pulse (see or dense enough to produce fusion like is a rich community of laboratories Figure 4); present efforts are focused on in a star, but plasma instabilities do using DPF machines for a wide variety achieving narrow-in-time pulses. produce some very local heating and of purposes, ranging from lithography some very energetic beams of deuterons. to plasma physics to nuclear physics.3 Improvements to performance, These cause neutrons to be emitted. The There has been a recent resurgence in repeatability, and reliability that NSTec neutrons are measured with various the use of these machines facilitated by has achieved are due to iteration and experimental diagnostics, and data much better theoretical tools that are characterization of tube design, source/ leading to improved understanding of drive tailoring, and characterization; whole process lasts but a few millionths the complex z-pinch process. are acquired. From start-to-finish, the Office of Research, Development, Test, and Evaluation sophisticatedVolume 4 | timing; Number firing 3 | Septemberand control 2014 12

Figure 3. Growth of the DD and DT neutron sources. The “Legacy” source was supplied to NSTec; using knowledge gained from it, the OneSys (133 kJ), TallBoy (500kJ), Gemini (1 MJ) and Sodium (350 kJ) sources were developed

Figure 2. A high speed framing camera photo of the z-pinch at maximum compression. The exposure time is 5 nano-seconds. The pinch is estimated to last between 20 and 50 nano-seconds. Figure 3. Growth of the DD and DT neutron sources. The “Legacy” source was supplied to NSTec; using knowledge gained from it, the OneSys (133 kJ), TallBoy (500 kJ), Gemini (1 MJ) and Sodium (350 kJ) sources were developed. LANL subsequently requested the fabrication of a more powerful DPF source that would burn DT gas systems; and concurrent modeling of all and make over 1013 14.1 MeV neutrons per pulse, in a single burst that is very narrow in time. Furthermore, the source is required to be compact in order to fit into the U1a tunnel complex at the production. NNSS as part of a future experiment series. processes from current flow to plasma Some examples of the increased Under development, a 350 kJ Sodium source has produced pulses of over 1013 14.1 MeV neutrons per experimental capacity developed by the pulse (Figure 4); present efforts are focused on achieving narrow‐in‐time pulses. DPF team are the ability to vary the yield of magnitude, the re-entrant chamber thatof a singleallows DPF very machine high neutron over fivedoses orders to be supplied to targets, the capability of producing narrow, intense single pulses of neutrons, and the ability to reliably, repeatedly, operate at high voltage and current levels. The NSTec DPF laboratories have been used by LANL, Lawrence Livermore National Laboratory, Sandia National Laboratories, the Atomic Weapons Establishment (United Kingdom), Figure 4. First day data from the startup of the 350 kJ “Sodium” source. Note the small research and development programs, shot-to-shot variation in yield, and the increase in yield resulting from use of DT mix and universities. For example, the DPFs versus pure deuterium. have been used for a wide variety of physics experiments, including stockpile stewardship instrumentation measure reactivity, are currently being stockpile. This class of experiment 4 development, Teller Light experiments, explored. The purpose of Fithisgure class 4. First of day data fromis similar the startup to a ofReaction the 350 kJHistory “Sodium” source. Note the and the measurement of physical experiment is to quantifysma thell shot neutron‐to‐shot variationmeasurement in yield, and the on increa priorse inunderground yield resulting from use of D‐T quantities such as material properties, multiplication (“chain reaction”) that nuclearmix ve rsustests, pure except deute inrium NDSE the nuclear cross-sections, and for is the fundamental mechanism that quantifying the performance of generates energy in nuclear weapons. pulse of neutrons injected around peak specialized systems, ranging from Neutron multiplication is extremely compressionfissions are initiated time, and by the a short, implosion intense is homeland security (e.g., radiochemistry sensitive to compressibility of materials, designed to remain below critical. activation experiments) to national and understanding compressibility under Page 3 of 4 defense issues (e.g., improvised the conditions encountered in a nuclear To be successful as one of several nuclear devices). weapon primary will be a key factor candidate pulsed neutron sources for in the NNSA developing Life Extension these experiments, the DPF will need to An Important New Application Program options (including pit reuse), generate a neutron pulse of the desired Important new applications such guarding against problematic aging as Neutron Diagnosed Subcritical effects, and establishing the safety/ Experiments (NDSE), which dynamically security characteristics for the future lessprofile than and ±100 a width nanoseconds, of 50 nanoseconds and produce (at 2 meters flight path), have a trigger jitter

Volume 4 | Number 3 | September 2014 Stockpile Stewardship Quarterly 13 a single neutron burst of at least 5x1012. 3V.A. Gribkov, “Current and Perspective The DPF is an existing candidate source Applications of Dense Plasma Focus for achieving these requirements and will Devices,” AIP Conference Proceedings, knownfirst atomic as Teller weapons. Light) In occurs a ground promptly or low be employed in static proof-of-principle Plasma and Fusion Science: 17th altitude detonation the fluorescence (also experiments over the next several years. IAEA Technical Meeting on Research Light is proposed as a nuclear forensic Using Small Fusion Devices, Vol. 996, technique.in the first few ● microseconds. Teller References Oct. 22-24, 2007, pp. 51-64. 1 J.W. Mather, Phys. of Fluids 8, 366, 1965. 4“Teller Light” is generated when 2N.V. Filippov, T.I. Fukuooiva, and radiation interacts with air. At the dawn V.P. Vinogradov, Nucl. Fusion Suppl. 2, of the nuclear era, Edward Teller used 577, 1962. it to measure the performance of the

General Atomics’ Target Fabrication Support for NNSA’s Secondary Assessment Technology Experiments on NNSA’s High Energy Density Facilities by Abbas Nikroo (General Atomics)

Target fabrication is essential to the Targets are carefully designed based on investments a large suite of capabilities, success of the experiments at the National the goals of the experiments through including coatings, precision machining, Nuclear Security Administration’s simulations utilizing models that are shell fabrication and characterization, (NNSA’s) high energy density (HED) subject to validation. The target is and introduced new techniques such facilities. Understanding nuclear weapon as laser machining and robotics, all performance relies on having models each geared towards realizing various dedicated and focused on producing of HED experiments with the goal of partsan assembly of the intendedof specific design components, in the high precision components and target adequately describing the behavior of laboratory experiment. Among these assemblies for the NNSA SSP mission materials under extreme conditions. The are components designed to provide (see Figure 1). While the range of targets are at the heart of these HED the drive (e.g., x-ray or magnetic), targets developed for the broader set experiments. They enable development of the materials under study, various of experiments is too large to describe models to understand material response in this article, below we present some and testing of those models in the and tracer diagnostic elements to assist examples of recent target platforms regime of HED, essential to the Stockpile inbacklighters deciphering used the as material flash x-ray under sources, developed and produced with major Stewardship Program (SSP). The unique extreme conditions. Components also involvement by the GA team in support collection of HED experimental facilities, enable data to verify that the desired of the Secondary Assessment Technology supported by General Atomics (GA) test conditions were indeed achieved. target fabrication, is available within The target assembly process has to fusion (ICF) experiments, in particular. bring these components together with subprogram and inertial confinement modeling of materials under extreme high precision (usually within several A major recent campaign at NIF has conditions.NNSA to fill Thesein the gapsHED infacilities the theoretical include examined deuterium-tritium (DT) Omega, Z, and the National Ignition facility and alignment with diagnostics. implosions, which are on a higher Facility (NIF). The Omega laser at the Hence,micrometers) production for proper and characterization fielding at the adiabat than the ignition point design, University of Rochester Laboratory for of the assembled target and its the so-called “high foot” campaign. Laser Energetics provides well over components that are faithful to the 1,000 shots per year to allow various intended design within the allowed experiments was only possible by highly experiments to be carried out in this tolerances is paramount to ensuring leveragingThe rapid fielding the infrastructure of the high developedfoot regard while training future stewards that the intended initial conditions for indirect drive implosions on NIF, in the process. The Z facility at Sandia were indeed present in the experiment. including cryogenic target fabrication. National Laboratories provides the Given the fragility of the assembled These implosions are high-performance capability to study unique dynamic implosions that are more robust against material properties, radiation effects, ablation-front Rayleigh-Taylor instability, and fusion experiments for relevant performedtargets and onsite logistics at theof fielding laboratory them that on have less convergence, and are generally materials ranging the entire periodic housesthe facilities, the facility. final assembly is usually less sensitive to modeling uncertainties. table. NIF allows access to extreme The goal of these experiments has physical conditions relevant to an As is the case with most targets, been to validate the codes in these operating nuclear weapon. Targets realization involves close collaboration lower convergence implosions where are provided for the collective set of in development and production between hydrodynamic mix is reduced, hence experiments performed at these facilities the GA target team and those at the possibly isolating mix as a cause for the along with the concomitant modeling NNSA national laboratories as well lower than expected performance of as the end users. GA has developed point design targets. This campaign has mentioned models. over time through NNSA and internal been highly successful, with simulations and simulations which refine the above Office of Research, Development, Test, and Evaluation Volume 4 | Number 3 | September 2014 14

(a)

5 mm (b)

(a) (b)

(c)

Figure 2. High foot campaign has used the NIF cryogenic target fabrication

rapidly for this campaign. A capsule with a Figure 1. In addition to traditional fabrication techniques, GA has implemented new infrastructure (a) is suspended to allow fielding with tents of targets inside processes such as laser machining and robotics to increase throughput while maintaining a gold lined DU hohlraum (b), which the precision required. The robotic arm shown above is used on a routine basis in fillis cooled tube using the Thermomechanical several different operations currently that involved much manual labor previously. (a) Package cryogenic refrigerator Thermomechanical Package subassembly for NIF cryogenic targets. (b) 50-µm gold dot gluing to diamond windows, a tedious manual assembly job previously, (c) Atomic force shown above. The capsule is laser- and microscopy, with throughput increasing from ~ 20 shells per day to over 1,000 in an hardwaretumble-polished in the finalto remove assembled isolated target overnight automated operation with the robot.

features to meet NIF specifications and correctly predicting many of the in a hohlraum platform for the has a 10-µm-diameter fill tube. implosion performance parameters, complex hydrodynamics effort. This including neutron yield. For target platform includes low density copper and shell fabrication capabilities fabrication in these experiments, some (Cu) foam (~ 0.9 g/cc) as part of a atreflector GA, a 25-micron-thick materials. Using aluminum the coating of the techniques included fabricating capsule under study. Development hemispherical shell was developed various components of the targets, of this experiment, as has become such as ultra-smooth plastic capsules the case for many others, involves spherical shape is important so that of varying thicknesses, polished to determining proper shock timing in a theto serve VISAR as diagnostic the reflector. can Again, observe the all keyhole target prior to the integrated three axes simultaneously, while the and laser polishing developed jointly implosion experiments. In addition, uniformity of the 25-micron wall (and “ignition” specifications using tumble by Lawrence Livermore National the development of targets that allow its characterization) is important Laboratory (LLNL) and GA, and observation and hence timing of to ensure shock transit times are shocks in multiple directions allow not affected by undesired thickness attached to the capsule with only 5 ng of examining the symmetry of drive containing 10-µm-diameter fill tubes glue to allow delivery of DT fuel. Another in these major directions. To allow optical test of the assembly at LLNL technique included gold-lined depleted viewing of shock break-out inside hasvariations demonstrated in the spherical that the reflector. spherical An uranium (DU) hohlraums developed for the spherical ablator in the required shape of the hemi shell was met (see these and other experiments. Finally, directions, the multiple axis keyhole Figure 3). GA has also been pursuing target fabrication for the campaign targets have been developed jointly development of low density Cu foam included precision assembly techniques by LLNL and GA. These have become itself using an aerogel technique, in to allow support of centering of the a workhorse for the ICF experiments, an attempt to improve on the current capsule inside the hohlraum to less than but this platform has been extended slip casting technique used at LLNL to provide the needed variation for that has a low fabrication yield of layering of the DT fuel was utilized to the Toto campaign. This target design approximately a few percent. Early 20 µm tolerance, and finally cryogenic allow availability of the proper targets required the addition of a special results are quite encouraging with for this campaign (see Figure 2). The Cu aerogel that is machinable and suite of experiments for this campaign the three axis keyhole ICF target has the desired <1-µm pore size (see spherical aluminum reflector to utilize also included the keyhole targets platform to perform shock break-out Figure 4). Experiments on NIF utilizing developed for shock timing experiments experiments in the material of choice, this platform are planned for late and the convergent ablator targets that the low density Cu foam. In this FY 2014 and beyond. image the ablator trajectory both in one and two dimensions. captures the shock breakout on the GA also provides the majority of targets configuration, the VISAR diagnostic used on the Z facility. One class of targets The Toto campaign is investigating which provides information on shock implosion of experimental capsules speedsinterior through spherical the reflective ablator surface,and the called “Cibola.” These targets support used for radiation flow experiments is

Volume 4 | Number 3 | September 2014 Stockpile Stewardship Quarterly 15

high temperatures and emits copious radiation. These radiation sources can be used to drive experiments, including opacity experiments for both fundamental science research (e.g., Fe) and for stockpile stewardship research (other high-Z materials). These targets involve efforts by both the GA and LANL target teams. GA scientists develop and fabricate the foam annuli that are nested inside the dynamic hohlraum itself to provide pulse shaping for the complex hydrodynamic shock breakout experiments. Image: Three axes target design radiation from imploding wire array. Figure 3. Two views of an aluminum spherical hemi shell fabricated as a reflector for Depending on the type of material involved, the opacity samples may concept, and assembly test results for reflectivity and focus. Assembly performed at LLNL. be provided by LANL, but again the onsite GA team performs the target (a) (b) (c) assembly at SNL, including mounting the opacity samples to the foams (see Figure 5). The concept of using an on-axis secondary hohlraum has been resurrected in some recent experiments with the secondary hohlraum placed above the wire array load to characterize the axial radiation energy.

The above touches on the breadth Figure 4. Low density Cu foam (~ 0.9 g/cc) is used in a number of experiments, including the so-called Toto platform used in the complex hydro effort by LLNL. GA has pursued an of areas where target fabrication, alternate development route for low density Cu foam using an aerogel technique as opposed particularly the effort at GA, has become to the slip casting technique that currently has a low fabrication yield of approximately a key enabling technology in support a few percent. The Cu aerogel has <1 µm pore size (a), can be diamond turned to shape of Secondary Assessment Technology (b), and does not have major voids as examined in x-ray tomography (c). Current effort to and ICF. One of the key functions GA produce samples large enough appropriate for the experiments at ~ 5 mm scale. performs is the iteration with the physics end users to simplify as much as possible very complex targets, and then LLNL’s Radiation Flow experiments on the Z facility. These targets are another development of materials needed and examples of collaboration between engineeringmake them possible of target through assemblies scientific to GA and LLNL target fabrication teams to jointly produce these complicated Collaboration among target fabrication targets. LLNL provides the portion of teamsrequired at GAspecifications and other labs, and functionality.and target the secondary hohlraum that holds fabrication and physics have been an essential component of this highly produces the rest of the target and successful effort. ● the radiation flow experiment, and GA all components onsite at SNL. These areperforms among the some final of target the most assembly complex of components that are machined for the Contact Us Z program using precision machining Please send your Figure 5. Assembled target for facilities at GA. “Cibola” platform supports comments about opacity shot on Z. The white central LLNL experiments on Z at a level of about cylinder ~ 14 mg/cc CH foam inside two weeks of experiments per year. this issue of the wire array assembly that is in the Stockpile turn supported by the top plate. A SNL devotes several weeks of Stewardship Quarterly secondary hohlraum is mounted in experiments per year to the Opacity and suggestions for future assembly to characterize axial radiation campaign. This campaign uses the issues to Terri Stone at terri. thisfrom configuration wire array. Inset: above Typical the wire opacity array “dynamic hohlraum” platform, which is [email protected]. To a nested pair of tungsten wire arrays subscribe to our mailing list, under study is mounted to the top plate imploding onto a foam annulus, which submit your full name, email configurationreceiving the radiationwhere an fromiron samplethe wire creates a collapsing hohlraum inside the address, and organization. array implosion. foam volume that reaches remarkably

Office of Research, Development, Test, and Evaluation Volume 4 | Number 3 | September 2014 16

In Memorium Heino Nitsche, 1949-2014

It is with great sadness that we learned of the passing of Professor Heino Nitsche of the University of California, Berkeley (UC Berkeley) in mid-July. Professor Nitsche was an outstanding scientist, leading

efforts in radiochemistry, heavy element research and a host of other scientific pursuits in chemistry radiochemistry.and nuclear physics. He was one of the first principal investigators funded when the Stewardship Science Academic Alliances program began—first in low energy nuclear science and more recently in Professor Nitsche attracted and inspired exceptional graduate students. Quite often, one of his team won an award for the best poster at the annual SSAA Symposium. Conversations with his students revealed that he was an excellent mentor effectively encouraging his students to achieve excellence in their careers. Professor Nitsche was born July 1949 in Munich, Germany. He earned his Ph.D. in 1980 in chemistry at the Freie Universität Berlin. He studied nuclear chemistry and electrochemistry and did experiments on the conductivity of uranium. He then joined the University of California, Berkeley as a Lawrence Berkeley National Laboratory staff scientist. He worked there for 13 years

returned to the University of California, Berkeley and became a full professor in the Department of Chemistry and the founding directorand in 1993 of the returned Glenn T. to Seaborg the newly Center. reunified He was Germany a world-renowned to direct a radiochemistry and accomplished research scientist institute in actinides in Dresden. whose In most1998, recent he

be missed. achievement was being part of the team that confirmed the existence of element 117, also known as ununseptium (Uus). He will

The FRIB is a new national user facility Highlights for nuclear science, funded by the Michigan State University (MSU), and the StateDepartment of Michigan. of Energy Office of Science, Funding Opportunity Announcement Located on campus and operated by The National Nuclear Security MSU, FRIB will provide intense beams Administration’s ( of rare isotopes (that is, short-lived Research, Development, Test, and nuclei not normally found on Earth). Evaluation recentlyNNSA’s) released Office the of latest FRIB will enable scientists to make funding opportunity annoucement discoveries about the properties of (FOA) of the Stewardship Science these rare isotopes in order to better Academic Alliances Program. This understand the physics of nuclei, FOA, Funding Opportunity Number nuclear astrophysics, fundamental DE-FOA-0001067, requests new interactions, and applications for society. and renewal proposals for grants in the research areas of Properties of Materials Under Extreme Conditions rareNazarewicz isotope hasscience been and a central has served figure on and/or Hydrodynamics; Low Energy manyin developing international the scientific advisory vision committees, for including the most recent National Nuclear Science; and Radiochemistry. Leda Experiment a Success The full posting is available at Research Council Decadal Study in Nuclear Science. Deep in the U1a tunnel at the GRANTS.GOV. The application due date Nevada National Security Site on is October 27, 2014. ● Nazarewicz is excited about the August 12, 2014, a device named challenge and looks forward to leading Leda imploded in the thick metal Stewardship Science Academic the establishment of a vibrant FRIB vessel shown above. Leda was a Alliances Program Grantee News Theory Center and helping the FRIB scaled, hydrodynamic experiment Stewardship Science using plutonium surrogate material Academic Alliances of FRIB. His role will be to articulate the and high explosives the scientists Program grantee Witek users realize the full scientific potential had been building for more than Nazarewicz has been the laboratory director and project a year. Scientists studied her data and proclaimed the Leda appointed Chief Scientist directorscientific on opportunities issues related with to science,FRIB, advise experiment a 100 percent success. at the Facility for Rare and to represent FRIB capabilities to the Congratulations to the Leda Team! Isotope Beams (FRIB). ●

broader scientific community. Volume 4 | Number 3 | September 2014 StockpileStockpile Stewardship Stewardship Quarterly Quarterly