KEK-PR0C--92-
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^ ,-*.«?* ?*! S-;V^ " > Proceedings of the 3rd Workshop on BALLOON-BORNE EXPERIMENTS WITH SUPERCONDUCTING MAGNET SPECTROMETERS
held at National Laboratory for High Energy Physics (KEK) February 24-25, 1992
Edited by Akira Yamamoto
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National Laboratory for High Energy Physics, 1992 KEK Reports are available from: Technical Information & Library National Laboratory for High Energy Physics 1-1 Oho, Tsukuba-shi Ibaraki-ken, 305 JAPAN Phone: 0298-64-1171 Telex: 3652-534 (Domestic) (0)3652-534 (International) Fax: 0298-64-4604 Cable: KEKOHO
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% Foreword
The Third Work Shop on Balloon Borne Experiment with a Superconducting Magnet Spectrometer was held at National Laboratory for High Energy Physics (KEK), Tsukuba, Japan on February 24 - 25, 1992. The workshop was supported by a Grant for Joint Research under The Monbusho International Scientific Research Program (No. 02044151). Two invited review talks were presented on " Progress of Measurement of Cosmic Ray Antiprotons and Search for Primordial Antimatter" and on " High Rate Data Acquisition System in Balloon Borne Experiments."
The main effort for this workshop was focused on the progress of the BESS (Balloon Borne Experiment with a Superconducting Spectrometer) experiment and on the scope for scientific investigation with the BESS detector. The progress was reviewed and further investigation was discussed for the BESS further scientific collaboration among Univ. of Tokyo, Kobe University, KEK, ISAS and NMSU. The 30 scientists and engineers participated to the workshop and there were extensive discussions to verify and to complete the BESS detector to be launched in Canada, this summer. New technologies for future balloon and space experiments were also discussed on triggering by using Neural Network and on Scientific investigation with Japanese Experimental Module (JEM) on the Space Station. The proceedings contains reports based on the talks given in the workshop and the proceedings may also be a progress report of the BESS collaboration. We would thank the Ministry of Education, Science and Culture for the Grant to support the BESS experiment. We deeply appreciate Prof. H. Sugawara, Director General of KEK, and Prof. S. Iwata, Director of Physics Division, for their continuous encouragements. Finally we would thank Mrs. S. Tanaka for her kind help to organize the workshop and to edit the proceedings.
March 1992 Akira Yamamoto Editor
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CONTENTS
Workshop Program ix 1. Plenary talks Measurement of Cosmic-ray Antiprotons and R. Golden 3 Search for Primordial Antimatter Progress of the BESS Experiment A. Yamamoto 9 2. BESS Detector Development Progress of Superconducting magnet Y. Makida 17 Progress of JET Chamber T. Yoshida 23 Progress of Inner and Outer Drift Chambers K. Yoshimura 33 Progress of Time-of-Flight Counters M. Nozaki 45 Mechanical Analysis for the BESS Structure H. Yamaoka 51 3. A Plenary Talk High Rate Data Acquisition System in B. Kimbell 61 Balloon Borne Experiments 4. BESS Electronics and Data Acquisition System Progress of Electronics K. Anraku 73 Progressof Data Acquisition System I. Ueda 81 Progress of Triggers System T. Saeki 87 Discussion Multi Track Triggers R. Golden 97 5. Technologies for Future Projects Track Trigger Using Neural System K. Taruma 103 Space Environment MonitoringSystem T. Doke 113 on the Space Station for common use in JEM
Appendix 1 Antiproton and Antimatter: A Balloon S. Onto 127 Experiment with Model Solenoid Appendix 2 Bess Technical Drawings J.Suzuki 143 K. Tanaka Appendix 3 List of Participants 173
\1 THE 3RD WORKSHOP ON
BALLOON-BORNE EXPERIMENTS WITH SUPERCONDUCTING MAGNET SPECTROMETERS
to be held at
KEK National Laboratory for High Energy Physics
Meeting Room, 1st floor, Main Laboratory
Feb., 24 - 25, 1992
*****pe5_ 24, (Mon,)***** [Plenary Talks]
10:30 Opening Address S. Orito (U. Tokyo) 10:40 Measurement of Cosmic-ray Antiprotons and R. Golden (NMSU) Search for Primordial Antimatter (Invited Talk)
11:40 The BESS status A. Yamamoto (KEK) 12:15 Lunch Break [BESS Detector Development] 13:15 BESS Tour at Experimental Hall 14:30 Progress of Superconducting Magnet Y. Makida (KEK) 15:00 Progress of JET Chamber T. Yoshida (U. Tokyo) 15:30 Coffee Break 15:45 Progress of Inner and Outer Drift Chambers K. Yoshimura (U. Tokyo) 16:15 Progress of Time-of-Flight Counters M. Nozaki (Kobe U,) 16:45 Mechanical Analysis for the BESS Structure H. Yamaoka (KEK) 17:15 Adjourn 18:00 Dinner at Ichinoya
IX I"
Plenary Talks
& ~n
Measurement of Cosmic-Ray Antiprotons and the Search for Primordial Antimatter
R. Golden
Introduction: Since we are all working hard on instruments to measure antiprotons and to search for primordial antimatter, it might be useful to step back from the hardware and look once again at the basic physics that motivated us in the beginning. In this talk we will review the various processes that could generate antimatter for us to study. We will also touch on the implications of various possible findings. Then we will review what is known at this time. Finally, I will close by summarizing what physics issues the first flight of BESS might address.
Why do we study "cosmic" antimatter? The role of antimatter in the creation and evolution of the Universe is not understood because there is very little data to help us build a detailed description of what happened. We do know, however, that tne fundamental interactions conserve baryons, at least to a very high degree in our present environment. Because of this conservation of baryons, there is much reason to believe that the big-bang was symmetric. But, as we shall see, both the symmetric and non- symmetric big bang theories have problems. The "smooth - symmetric" big bang was the first proposed model. In this model, the universe expanded and cooled reaching a point where the average photon energy decreased to about 1 GeV. At this point, the universe would have consisted of a "gas" containing roughly equal numbers of protons, antiprotons and photons. As the temperature dropped further, the protons and antiprotons would be "frozen out" with photon-photon collisions no longer able to create new baryon-anti baryon pairs. From this point on, protons and antiprotons would annihilate finally reducing the density until the mean-time between chance encounters approaches the age of the universe. The resulting universe would be very diffuse and have a very high photon/baryon ratio (about 1018:1). The formation of stars and galaxies, etc., would be extremely unlikely. Clearly our universe began differently...but how can we change the smooth-symmetric picture into something more workable? We could just make the ad-hoc assumption that the initial baryon number of the universe was not zero. But this is unsatisfactory to most persons because it postulates that one type of matter was preferred over another. During the 1960's a number of persons investigated other possible separation mechanisms (electromagnetic, etc.) which could separate the universe into domains alternating between matter and antimatter in their dominant form. Unfortunately none of these mechanisms found wide-spread acceptance. Another class of theories follows the same beginnings as the smooth- symmetric big bang but at some point before the proton-anti proton freeze-out, another process intervenes. In general, this other process involves heavier particles (perhaps even the 101* GeV GUTS vector bosons). These heavier particles and their antiparticles undergo a baryon non-conserving decay, with a higher decay rate for the anti-particle that for the particle of ordinary matter. The net result is that there are more "parents" who will give rise to protons than there are "parents" that can give rise to antiprotons. Note that this process involves both baryon non-conservation (which has NEVER been observed) and CP violation (which has been observed in weak interactions). Many people are disturbed by the requirement in this theory for baryon non-conservation. In addition this class of theories still requires that one type of matter be preferred over another. In an attempt to overcome the last objective, Floyd Stecker has proposed that the CP violation be regional, with some portions the universe having preference for matter and other portions having a preference for antimatter. This leads to a universe organized into domains of matter and antimatter but no one knows what the size of these domains might be. There are other processes taking place in the universe that also produce antimatter. Some of these are less exotic than others, but in each case, the rarity of antimatter in our part of the universe, may allow us to study these processes by observing their antimatter by-products in cosmic rays. These processes include: Production of p and e+ by cosmic ray interactions Possible pair-production near black holes (the Hawking effect) Production of antimatter in other exotic environments Possible production by decay of super heavy particles
What can we learn by photon-related observations? Visual observations of stars, etc., do not give useful information regarding the possible presence of antimatter. This is because visual photons are generated by th. .rial and atomic processes. The light emitted by these processes has the same spectra whether the material involved is matter or antimatter. However, X and Y - ray spectra can be useful. In the X-ray region, annihilation of e+ and e" gives rise to a X-rays of 0.51 MeV energy. Broadening of this line emission should be quite small, arising only from bulk motion of the annihilation region. Annihilation of p and protons gives rise to meson production. In particular, n° mesons which decay in to two 70-MeV y - rays. Unfortunately, in this case the rc° can be produced with a wide range of energies. The resulting y - ray spectrum is quite broad. Because of the broad spectrum, and the existence of alternate ways for producing jt° , unambiguous recognition of p - p annihilation would be difficult. To date, no clear evidence of antiproton-proton annihilation has been observed in the y - ray spectra. However evidence for electron-positron annihilation spectra has been observed. Line-emission at 0.51 MeV has been observed . .ear the galactic center. It is interesting to note that this emission varies dramatically in time. The suggestion is that positrons and electrons are being formed in very energetic processes (perhaps by conversion of y-rays produced by matter falling in to a black hole).
What can we learn by cosmic-ray observations?
Cosmic rays provide a sample of extra-solar material. If there are stars made of anti-hydrogen burning to form anti-helium, then we might expect that some of these stars may eventually super-nova and contribute a portion of their antimatter to the cosmic rays. Their presence could then be detected in the form of complex (that is: composed of more than one nucleon, anti helium for example) antinuclear in the cosmic rays. As we shall see in the next section, anti-nuclei searches have not revealed any antinuclei. However, positrons and anti-protons have been observed. In subsequent sections we will summarize those observations.
The Search for Antinuclei: Figure 1 shows the results of numerous searches for antinuclei. As CaUta ft il(H7l){I>!) can be readily seer;, no antinuclei have been found. The present upper limit is Tirai (II7I) about 7 x 10~5 for anti-helium / helium at the 95% confidence level. This is •itt*ir it tl. |1I71) I- H H sufficient to assure that our galaxy does : i 10-' tTllttl (1l7t) not contain any anti-stars. The reasoning Unl tt tl. (1175) is as follows: Since the cosmic rays are dominantly matter, the stars in our neighborhood of the galaxy must be 0 -4 ordinary matter. If our portion of the « 10 !»oit it il. (UTS] (l>!) - Ctldti tl il. (1IBZ) galaxy adjoined another portion of the galaxy that was dominantly antimatter, then the region where these two regions joined would be a very strong emitter of y-rays. Since no such regions are observed, we conclude that our galaxy is Ki|iditj (GV) entirely composed of ordinary matter. Figure 1. Results of the Searches for Antinuclei Antiproton • • i i—•- Observations: wizard— mod. iMky box Stroltmattar ot •] WlZu-d—mod. oloood ••IAXJ 3alam«i «t •! Figure 2 shows the Cotdon *t «1 (uppor limits onlj antiproton observations Boaomolor ot oj 10 reported to date. The figure also includes predictions for the WiZard 10 Astromag experiment. The predictions are made a. by assuming that the antiprotons are produced proton by interactions with the •plllov*^ interstellar medium. The 10" amount of interstellar 100 1000 medium required for the KE/nucl (GeV/n) observed antiproton/proton ratio is Figure 2. Antiproton Observations and Predictions somewhat higher than the amount expected by studying other components of the cosmic ray flux. To further understand what we might observe, we will look at three different energy regions: At low energies (1 GeV«) no secondary antiprotons are expected. This is because the production process (collisions of cosmic rays with interstellar gas) gives rise to antiprotons produced in a system with a rapidly moving center of mass. Consequently, there is a lower limit to the energy with which the antiprotons can be produced. Thus this region is essentially a "window" to antiprotons produced by more exotic processes (such as decay or annihilation of super-heavy particles) In the intermediate energies (1-20 GeV) antiproton production is higher than, but consistent with secondary production. One way to look at this region, is that antiproton observations here can tell us how much material is traversed by the "parent" protons that collided with the interstellar material. At the highest energies (»20 GeV), the predictions become sensitive to how cosmic rays are stored in the galaxy. The two WiZard predictions correspond to two extreme conditions: a)lower-curve: cosmic rays readily leak from the galaxy and b)upper-curve: cosmic rays are totally confined to the galaxy.
Positron Observations: Positrons, like antiprotons, can be produced as a result of cosmic ray collisions with the interstellar medium. During such collisions JI+ and K+ are produced which decay, eventually resulting in positrons. These positrons are produced at roughly the same rate as the antiprotons. They have a similar production energy spectrum as antiprotons except that positrons can be produced at energies below 1 GeV. A major difference between the positron and antiproton physics is that positrons can be expected to lose energy during propagation due to radiative interactions (for example, synchrotron radiation and inverse-compton scattering with the 3° K blackbody radiation). At high energies the radiative losses become so big that any observed high energy positrons MUST have come from a nearby source! The e+/(e+ + e") data are shown in Figure 3. Note the apparent rise above 20 GeV. This may be indicative of a change in the mechanism for producing positrons. It has been speculated that at lower energies, we are seeing positrons produced as secondaries, but at high O Coldaa «t *1 'B7 7 Mullvr I, Tuc 'I energies, we may be seeing positrons produced by conversion of g-rays in some energetic nearby source. In the latter case Energy (GeV) we would expect that the e+/(e+ + Figure 3. Positron/(positron+electron) Ratios. e-) ratio would approach 50%. Unfortunately, these energies correspond to the extreme limits of many of the experiments. It is possible that the apparent up-turn is due to contamination of the e+ samples with miss- identified protons.
Summary: The upcoming BESS flight will be able to measure as many as 107 helium nuclei during a 10 hour flight. This will allow sufficient sensitivity to assure that even helium nuclei from our neighbor galaxies will be encountered. This is a major qualitative advance in the search for primordial antimatter. The flight will also allow observation of antiprotons in the region of a few hundred MeV to perhaps a little over 1 GeV. As can be seen from Figure 2, this is a most interesting region. The lower energy range will cover an area where only exotic process can contribute. The upper energy range will allow observation of antiprotons near the kinematic lower limit for secondary production. The exact location and shape of this region should allow very useful conclusions regarding the hypothesis of secondary production as well as the possibility of energy-changing mechanisms that are operative as the particles propagate. Future flights of the BESS instrument, equipped to distinguish positrons from protons, offer an exciting opportunity. -*
PROGRESS OF THE BESS EXPERIMENT
Akira Yamamoto
National Laboratory for High Energy Physics ( KEK )
1. INTRODUCTION
A balloon borne experiment with a superconducting solenoid spectrometer (BESS) is being prepared in an international collaboration among the University of Tokyo (Tokyo), Kobe University (Kobe), National Laboratoy for High Energy Physics (KEK), the Institute of Space and Aeronautical Science (ISAS) and New Mexico State University (NMSU). Primary scientific objectives of the co operative experiment is precise measurements of antiproton, positron and gamma ray spectra in cosmic rays and search for primodial antimatter in universe. A key technology in the BESS experiment is a superconducting spectrometer consisting of a thin superconducting solenoid magnet and a sophisticated particle detector system in clyrindrical configuration. It enables us to provide a wide angle particle spectrometer with a solid-angle acceptance of 1 m2- sr and to measure antiproton abundance to proton's down to a level of 10"6 and to search for antihelium evidence in a level 10"°- The detector system including the superconducting magnet has been completed and is being prepared for an intending scientific balloon flight in Canada, summer, 1992. This project was initiated in 1985 to study of technical feasibility for ASTROMAG project to measure comic rays and to search for primodial antimatter on the Space Station. The scientific balloon
Layout of the detector -t
experiment program has been established among those universities and institutions scince 1989. The hystrical background and progress of the BESS experiment are briefly summarized as follows:
1985: Thin solenoid spectrometer configuration was proposed by A. Yamamoto et. al., cosmic- ray detector on the Space Station as a candidate ASTROMAG configuration. [1] 1986: Development of a thin superconducting solenoid magnet started at KEK. Cosmic-ray antimatter search experiment with multiwire drift chambers in permanent magnetic field was proposed by S. Orito et.al., and development of the detector system was started at University of Tokyo. [2] 1987: Present cylindrical detector configuration consisting of a thin superconducting solenoid magnet, multiwire drift chambers and TOF counters was determined and the experiment preperation was started. [3]
1989: The BESS collaboration established among the U.of Tokyo, KEK, ISAS and NMSU. Technical flight test of the central tracker successfully made at Sanriku, Japan. [4] 1990: The BESS spectrometer was nearly completed and accelerator beam test was started. NASA-ISAS started to discuss a global collaboration for superconducting spectrometers and scientific investigation. 1991: A scientific flight at Lynn Lake was planned but postponed. 1992: Scientific balloon flights planned to be carried out at Lynn lake, Canada.
2. BESS SPECTROMETER
The BESS spectrometer has a unique feature of cylindrical configuration with a solid angle acceptance of 1 m2.sr corresponding one order of magnitude larger acceptance than existing balloon magnetic spectrometers. A thin superconducting spectrometer magnet which provide a uniform magnetic field of 1 (- 1.2) Tesla in a volume of 1 m in diameter and 1 m in length. The detector sytem consists of TOF counters and a set of sophisticated cylindrical multiwire drift chambers, which are installed inside and outside of the solenoid and may define particle trajectries in terms both of sagita and deflection angle in the magnetic field with nominal track smpling points of 50. It easily enables us to identify particle charge precisely. The BESS spectrometer may realize to measure antiproton abundance to proton's down to a level of 10"^ and to search for antihelium evidence in a level 10"8- Main parameters of the detector system are summarized in Table 1.
3. SCIENTIFIC FLIGHT IN CANADA
A scientific flight is planned to be launched at Lynn Lake in Canada, summer, 1992. The first shipping of instrmentation is scheduled in the end of February and the main shipment is to be in May, 1992. We have a plan to arrive at Lynn Lake on June 1, for preparation of the BESS instrumenitation . The BESS spectrometer shall be ready for the flight by July 13.
REFERENCES [1] A. Yamamoto .ASTROMAG Workshop ISAS (1986) A. Yamamoto et al., IEEE Trans. MAG. Vol. 24, No.2, (1988) P.1421 [2] S. Orito et al., ASTROMAG Workshop, ISAS (1986) [3] Edited by J. Nishimura et al. Proc. of ASTROMAG Workshop, KEK 87-19 (1989) [4] Established at the 1st BESS Workshop, KEK, Tsukuba Feb. (1988)
in- r Table 1. Main Parameters of the BESS Detector
General Dimensions 2 m x 2 m x 3.2 m (1.7 mfx 3.2 m) Weight 1.8 tonf Acceptance I m^-sr Operational duration (max.) 5 days Superconducting Magnet Dimensions: Coil Size 1.0 mfx 1.3 m Useful Aperture 0.85 mfx 1.0 m Transparency 0.2 Xo (radiation length) 0.06 (interaction length) Weigh t 400 kg LHe Storage Capacity 150 L LHe Refill. Inter - period 5 days Particle Detectors Acceptance 1 mAsr Momentum Range < 1 GeV / c (with particle ID) Overall Size (Pressure Vessel) 1.5 m dia x 3.2 m Tracking Devices Central Tracker: JET Chamber Tracking Volume 0.75 raifxl.Om # of Sampling 50 in max Gas C02 (90%) + Ar(10%) Slow Gas Spatial Resolution (x) 200 |im (z) 1 cm (charge div) Max. Det. Momentum 300 GeV/c Pre-Trigger & z Position Cylindrical Inner and Outer drif chamb (IDC) (ODC) Coverage (+ / -)f Angle 78deg 71.5 deg Half Cell Size 44.6 / 46.6 mm 47.2 / 48.9 mm Tracking Mean Radius 391/411 mm 605/627 mm Tracking Length 1 m 1.08 m # of Cell/Chamber 11/12 15/16 Gas (Slow Gas) CO2(90%) + Ar(10%) Spatial Resolution (f) 200 urn* 200 urn* (z) 500 urn 500u.m* TOF Counters Scintillator NE102A Photomultiplier Hamamatsu - R2611 - sx # of Segmentation 8 each at top and bottom Time Resolution 200 psec (@ B=3 kGauss) Data Aquisition Data gathering rate 1kHz Data recording rate aprox. 500 kbytes/s (peak) Capacity of data recorder 2 x 5GBytes Kinetic Energy (GeV) Figure 1; Antiproton to proton ratio in the galactic cosmic rays. From Stochaj (1990); open circles Golden et al. (1979, 1984); filled circle Buffington Schindlcr and Pennypacker (1981); filled square Bogomolov et al. (1987); filled triangle Ahlen et al. 1988 and Salamon et al. (1990): filled hexagon Streitmarteret al. (1989,1990) and Stochaj (1990).
component of magnetic field
Fig. 2. BESS launch site, Lynn Lake, and relative vertical earth magnetic field component Fig. 3. BESS DETECTOR INTEGRATION • """•-*•»-
Drift Velodty 7.0 Time Offset 0S50
Triggered Track r y-, vr-, •;)•-, vr-rar^ TTTT'T- 'aya^
Z-coordinates were determined from • the charges deposited on N both wire ends
,.' •!•' .1.' -i.' .V.'M.' •!.' .l.'HA TO(» N/1EW • iDC v^CW
EVENT* 1 TRG 8 TME 12h 51m 32s 112 PREVIOUS: 0
Typical negative charged track in the beam test (1050 Mev/c Negative) ^— - . . . Tf
f
BESS Detector Development
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PROGRESS OF SUPERCONDUCTING MAGNET
Y. Makida, Y. Doi, T. Haruyama, H. Inoue, N. Kimura, S. Saitou, K. Tanaka, H. Yamaoka and A. Yamamoto
Nat'l Lab. for High Energy Physics ( KEK ) Tsukuba, Ibaraki, JAPAN
ABSTRACT
A thin superconducting solenoid of 1 m
INTRODUCTION
A thin superconducting solenoid has been developed at KEK for balloon-borne experiments in high energy particle astrophysics.'~2 It is to be launched up to an altitude of about 35 km to search for cosmic ray antimatter ( BESS collaboration )3. Figure 1 shows an outlook of the magnet. It has an inner warm bore of 0.8 m
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~^%> Fig. 1. Outlook of the thin solenoid. MAGNET DESIGN
A general layout of the magnet is shown in Fig. 2 and main parameters are summarized in Table 1. A superconducting solenoid is installed in a. double cylindrical vacuum vessel. The coil that was wound with an aluminum stabilized superconductor is supported by an outer cylinder made of high strength aluminum alloy (2219-t851). A toroidal shaped liquid helium reservoir tank with a capacity of 150 1 was welded at one end of the cylinder. The coil is cooled by only thermal conduction through the outer cylinder ( static indirect cooling )'. This cooling method is more reliable than the forced cooling method under balloon flight condition, because of no needs for active elements. The bath cooling method was not applied due to disadvantages of thick wall of a cryostat for the detection of cosmic rays and of heavy weight for the launch. We have understood that the indirect cooling has less dynamic cooling power. We have measured coil temperature rises according AC loss during current changing. Hut temperature rise could be acceptable enough during normal charge and discharge.
Table 1. Main Parameters of the Solenoid Dimensions: coil diamer 1.0 m length 1.3 m thickness (center) 5.2 mm (end notch) 10.4mm Support cylinder material A2219 thickness (center) 2 mm (end notch) 4 mm Cryostat: outer diameter 1.18 m length 2.0 m material (outer cylinder) aluminum honeycomb LHe capacity 150 1 Useful aperture 0.85 m length 1.0 in Central field 1.2 T Bmax in coil 2.2 T Current 520 A Turns 3383 Inductance 6.03 H Stored energy 815 kJ Wall thickness 0.21 Xo Total weight 430 kg Conductor : Superconductor NbTi/Cu Stabilizer Pure Al (99.999%) RRR >1000 NbTi : Cu : Al 1 : 1 : 7.3 Outer size 1.2 x 1.8 mm2 Ic (@ 3.8 T, 4.2 K) 930 A i. sulation Polyvinyl formal 2200
1460 [ALUMINUM HONEYCOMB)
Iff
\ ^RADIATION SHIELD V«UUM VESSEL U 'SUPPORTIR-AXIS) 'SUPPORT IZ-AXISI 'SUPERCONDUCTING COIL
Fig .2. Cross sectional view of the solenoid.
We have adoped a new reliable protection system for this coil using pure aluminum strips ( PAS )!, which have been laminated on the inner surface of the solenoid. The PAS are expected to increase net axial thermal conductivity ( Kz ), namely, axial propagation velocity ( Vz ), resulting in a homogenized energy dump into the entire coil.
EXCITATION OF THE MAGNET
The magnet ha3 been successfully charged at a nominal field of 1.2 T at 512 A in the persistent current mode. The field decayed with a satisfactorily long time constant of 900 years. A lifetime of liquid helium in the reservoir was 6 days. Therefore this facility assures a balloon-borne experiment detecting cosmic rays for 6 days.
QUENCH CHARACTERISTICS*5
Quenchs have been driven by means of a film heater with a resistance of 5 Q which deposits a point disturbance onto the inner solenoid surface. The heater with an area of 3 x 9 mm2 spreads over three conductors. Thermometers measured temperature rise after quench. Voltage taps were also located moderately at 11 points in the coil. Figure 3 shows traces of heater quench test at 450 A. The energy deposited by the heater was 1.26 J ( 1.4 W x 0.9 sec ), and less disturbance could not cause quench. Since liquid helium in the reservoir tank is indirectly connected through thermal conductivity of the support cylinder, any sharp pressure rises in the reservoir tank were not observed. 120
<9 E • (.-» _JL-ib ) (c) ^^-~~^—
J60 / 1 jjllil^ (d) / feu—-— i.jl.O 30 W0.5 i/i uj or / M).0 "-0.0 0 4 6 8 10 12 14 18 20 TIME Csecj Fig.3. Traces of measurements at heater quench test at 450 A. (a):Balance voltage for detection of a quench, (b):Heat load of 1.4 W (cJ.-Tomporature at heated point, (d):Field, (e).-Pressure in Lhe reservoir
Fig. 4. Photograph of the coil part with pure aluminum strips. SHOCK ABSORPTION TEST
Besides the quench test, this magnet have been examined on shock absorption, because the magnet will meet mechanical impulse of 2 G and 10 G at takeoff and landing respectively, especially at the former the magnet will be excited in a persistent current mode. To confirm a stability against impulses during balloon flight, the magnet was freely dropped from a height of several mm, and it was stable against such impulse of 4G in maximum at a collision with ground. Only small vibration of a balance voltage for quench detection was observed. We are convinced of no outbreak of quench at takeoff.
INSTRUMENTS FOR BALLOON FLIGHT
Regulation of reservoir tank pressure and telemetric trigger of PCS are most important instruments. Fig. 5 shows a flow diagram of the magnet. Pressure is normally regulatpd by two check valves with the cracking pressure of 1.1 kg/cm2 abs ( 15.2 psi ) at the entrance of shield cooling line and current leads cooling line( C/L line ). These check valves are run independently of atmospheric pressure by referring to a vacuum cell in itself. Since flow resistance of shield cooling line is larger than that of C/L line, so a manual valve is added into the C/L line to pass vapor He gas through shield line as much as possible, which lower the flow rate at a minimum necessary value of 4 N H /min. During charges on the ground, C/L need vapor gas of 70 N 9. /min, so a bypass is also added into the C/L line. Other check valves shown in Fig. 5 run in case of emergency. The magnet must be discharged before a descent. Heater in the PCS is fired by exclusive batteries, and this operation is telemetric triggered. If the PCS should not turn off, quench heaters will be fired by their exclusive batteries. We have not confirm the operation yet, and we must do it as soon as possible.
Fig. 5. Flow diagrame of the magnet
CONCLUSIONS A performance test of a thin superconducting solenoid for balloon borne experiments has been carried out. The magnet has been successfully excited up to 1.2 T ( at 512 A ) and is being preparated for an intending balloon flight. In order to avoid localized heating, a new concept of homogeneous energy dump by pure aluminum strips that raise propagation velocity was introduced for this coil. Their efficiency has been confirmed through heater quench tests. REFERENCES A. Yamamoto et al, Conceptual design of a thin superconducting solenoid for particle astrophysics, IEEE Trans, on Magnetics, 24:1421-1424 (1988) Y. Makida et al, Developement of a thin superconducting solenoid for particle astrophysics, in: "Proc. of MT-11", Tsukuba, JAPAN (1989), p. 1341 S. Orito, Antiproton and antimater : a balloon experiment with the model solenoid, in: "Proc. of the Astromag workshop", KEK report, KEK87-19 (1987), pill M. N. Wilson, "Superconducting magnets", Oxford Univ. Press., Oxford, UK (1983) Y. Makida et al, Performance of a thin superconducting solenoid for particle astrophysics. Adv. in Cryogenic Engineering, 37 (1991) fim&"3i
INSTALLATION OF THE SUPERCONDUCTING MAGNET
f Progress of JET Chamber
presented by T. Yoshida
24 February 1992
A cylindrical drift chamber is placed inside the superconducting magnet and serves as a central tracking device of the BESS detector. This chamber provides the trajectories of the charged particles that determine the charge and the momentum of the particles. The trajectory of the particles are measured about 40 ~ 50 points over the magnetic field volume. With this configuration, we can eliminate the background of the positive-charged particles faking a negative-charged track due to the large angle scattering. We can see the kink of these fake tracks directly and can reject them. The requirements of this chamber are:
• It has to be rigid mechanical structure against the shocks from the launching and the landing of the detector but the weight of the chamber should be light,
• The materials of the chamber should be small to reduce the multiple scattering of the particles across the chamber,
• Using the low-power slow read-out electronics, it has to provide good three-dimensional spatial coordinates of the tracks and to separate two or more tracks closed each other.
Structure
The sensitive volume of the jet chamber is a cylinder with the length and the diameter of 1 m and 75.4 cm, respectively. The chamber is subdivided into four cells, two of them contains a plane of 32 signal wires and the others contains 52 signal wires. The sense wires, the tungsten- rhenium alloy of 20 /im, are equally spaced by 13.4 mm alternating the potential wires, the aluminum wires of 200 /im. In order to resolve the left-right ambiguity, the sense wires are staggered by 500 /im alternating to the left and right side of the plane defined by the potential wires. Cathode wire planes form boundaries between the cells. The aluminum wires of 250 /im are equally spaced by 6.7 mm. The maximum drift distance of one cell is 95 mm.
In order to reduce the weight of the chamber, the cylindrical wall was made of the Aramid honeycomb. Inside and outside of the honeycomb, the KAPTON sheets are glued. On the inner KAPTON sheet, the electric-field shaping cages are formed by the copper etched pattern. Two end plate are made of aluminum of 25 mm. This width is enough to support the stretching forces of the signal wires ( 40 gw ), the potential wires ( 300 gw ) and the cathode wires ( 400 gw ). Total weight of the jet chamber is about 60 kg.
*- -T"*-*- -*
The construction of the jet chamber started on the beginning of 1988 and completed on 1989. The test flight was performed at Sanriku on 1989, and there was no damage on the jet chamber during the test flight.
Readout electronics
Low noise preamplifiers are mounted on the end plates close to the points where the signal wires are attached. The signal of one signal wire is read from both end to provide the track coordinate along the wire by the charge division method. The gain of the preamplifier is 7 mV/,uA, and the input impedance is about 130 Q. In order to reduce the noise of the preamplifiers, they are shielded by the aluminum plate. The signals from the preamplifier are transported by the twisted-pair cables to the digitizing electronics.
The waveform of the signals are digitized with 30 MHz flash analog-to-digital converters (FADCs). The FADCs have a 8-bit resolution. Only the data whose amplitude exceed the predefined threshold are recorded to the first-in-first-out (FIFO) memory. After the end of the conversion of the FADCs, the data in the FIFO memory are compressed by the hardware electronics ( the compressor module ), and we can get the timing, the width and the total charge of the signal.
128 channel of FADCs are now available for the jet chamber. 80 signal wires are read by FADCs and 48 of them are read from both end of the wire to provide z-coordinate along the wire.
Gas
The requirements for the gas used for the jet chamber are:
• In order to achieve good spatial resolution and good double track separation using the slow electronics, the drift velocity of the gas has to be slow and the longitudinal diffusion of the drift electron should be small.
• To enhance the signal-to-noise ratio and to reduce the fluctuation of the arrival timing of the drift electron, the number of ionization per unit length along the track should be large.
• The gas has to be non-framable, easy to purchase and the price of the gas should be cheap.
The gas mixture of 90 % CO2 + 10 % Ar is satisfied above requirements. The drift velocity of this gas is about 7 ram//is under the conditions that the electric field is equal to 1 kV/cm and the pressure of the gas is 1 atm. The drift velocity of proportional to the strength of the electric field. The longitudinal diffusion of this gas is less than luC' /im at 1 cm under the same conditions described above. The number of ionization of the minimum ionized particle is about 100 per 1 cm.
- L' I - K-^ »—
The volume inside the jet chamber is filled by this gas. Suppling the high voltages for the potential wires and the cathode wires of -2.74 kV, and -12.34 kV, respectively, the strength of the electric field in the jet ch&mbet is 1.0 kV/'cm. The measured drift velocity is a.hout 7.5 (im ( preliminary ). The deflection angle with respect to the electric field in the magnetic field of 1 Tesla is calculated to be about 5 degrees. Typical pulse amplitude of the preamplifled signal is 100 raV against the noise level of a few millivolts ( \tJ ).
Performance
The expected average space resolution in the drift direction is about 200 fim, and the one along the wire is about 1 cm. Assuming these resolutions and the magnetic field of 1 Tesla, the momentum resolution of this chamber is ^f = 0.3 %/(GeV): the maximum detectable rigidity is to be 300 GV. This momentum resolution allows us to expect a factor 108 rejection against positively charged tracks faking a negative track in the momentum range below a few 10 GeV/c.
The figure attached to this report shows a multi-track cosmic-ray event recorded in 6th July 1991 without the magnetic field. Since the left-right ambiguity of the hits was not resolved, each hit is plotted both side of the signal wire plane. As shown in the figure, the left-right ambiguity can be easily resolved. The double track resolution is less than 3 mm. The spatial resolution of the direction along the wire is also studied using the data recorded in the beam test performed in December 1991. Excluding the systematic errors due to the miscalibration of the gains of the amplifiers, the resolution of z-direction is about 1 ~ 2 cm. The precise calibrations of the jet chamber will be performed using the cosmic-ray events with and without the magnetic field.
Current status
The maintenance of the jet chamber has been continued for two years. Improving the connec tions between the body of the chamber and the ground of the read-out electronics, the noise level on the signal was reduced. The high-voltage power supplies are also developed in order to avoid the damages from the thermal problem. Now we can operate the jet chamber system very stably.
We should continue some efforts to keep the gas inside the chamber pure in order to perform more stable operation under the condition that the gas flow into the jet chamber is stopped. Some gas systems to keep high purity of the gas are now under consideration.
We also have to study the parameters of the jet chamber system. The relation between the distance of a hit from the signal wire and the timing of the signal from the trigger signal (x-t relation) should be mapped from the data of the cosmic-ray events. This relation will be a function of the angle between the trajectory and the signal wire plane. The gain of the amplifiers has to calibrate using the test pulse input. After the calibration of the amplifiers, we can obtain the z-coordinates of the hits. The deflection angle of the drift electrons with respect to the electric field should be estimated. We will study these chamber parameters using the cosmic-ray event data that will be recorded after this workshop. Event § 61 Tr i gqer 1ff2t2i Event timing "EES5~ CAMAC .... JL5S EAQC S40 011:11:05.7937 1 2 4 5 6 •*U •*$> TOF counters S 7 8 "" " f?> 9 10 1 1 12
ODC (not operated)
ODC (not operated)
Fig.l. Cosmicray three track event The charge division method to measure Z-coordinate
^VVr -W
Ck Avalanche point K L : Wire length R.: Wire resistance q : Preamplifier input resistance
ri+^R:ri+(l-^)R = Qb:Q1
x = (R-f rQQb-rjQ, L R(Q,+Qb)
Wire staggering to solve the left-right ambiguity
j ; q \ True track
Fig. 2 301 Cathod wires
(a) Field shaper HV supply system
777"
-3.3kV Jet Chamber \ Erectric field at the surface of the sense wires 430kV/cm Electric field at the surface of the potential wires below 20kV/cm
176 Potential wires
(b) Potential wire HV supply system I s *
s
-:-;i- -f
Progress of Inner and Outer Drift Chambers
Koji Yoshimura
University of Tokyo 7-3-1 Hongo Bunkyo-ku Tokyo Japan
Introduction
For the study of the cosmic ray with Balloon in High altitude, it is necessary to select the events out of the high rate background positive charged particle from the viewpoint of data taking and data storage ability. BESS detector is equiped with Inner and Outer Drift Chamber (IDC.ODC) for this purpose. Each chamber is composed of about 50mm drift cell and give 5bit hitpattern of particle trajectory. Total 20bit hitpattem is analyzed with second level track trigger logic, consist of hardware with ROM look-up table, so that event rate is reduced to the Ik events/sec that data taking system requires.
In addition to the track trigger, they perform as intrinsic drift chambers and give information about the position of incident track . Good resolution along Z axis with diamond shaped vernier pad as well as r<}> resolution with drift timing measurement enable us to reconstruct events in 3D space.We can decide the incident direction of converted "y ray in the magnet with an error below 1 degree and search the vertex point of multiple track caused by the upper material.
Design
Schematic view of IDC and ODC is shown in Fig.l. IDC(ODC) is 1.06m long (l.I8m long) , 36mm (44mm) thickness chamber located between radii of 384mm (594mm) and 420mm (638mm) and is covering the polar angle from 8° (18°)to 172° .(162°) Both chambers are almost identical except for dimension and strength of magnetice field-lTesla for IDC, about 0. ITesla for ODC. Mechanical structure of each chamber is composed of 4 honeycomb panels and G10 endplates and side plates We honeycomb panels to reduce weight and material causing multiple scatttering and interaction of the incident particle. Fig.2 shows nj) crosssectional view. Skin of the panel is made of 18mm copper ,and 125 mm KAPTON sheet. Outermost skin is covered with 0.5mm aluminum sheet for increasie mechanikal strength. Inner skin is etched to forms 1.5mm width electric field shaper at 3mm interval and pair of 7.5mm vernier pad surrrounding the sense wire. Inside of chamber is devided into two 12mm thick layer. At the center of each layer .sense wires and field wires are streched with about 50mm spacing alternatively through DELRIN.feedthrough. Wire position of two layers are staggered by wire spacing to resolve left right ambiguity This wire configuration gives also self calibration scheme using the sum of drift time of both layers, which is almost constant.
25|im gold plated Tungsten-Rhenium .wire is used for sense wire and 250|im gold plated aluminum wire for field wire. Both wire is streched with tension of 55gw and 400gw
-33- respectively. Before fixed wire with solder, we give more pretension of 15gw and 40gw so as to minimize creeping in long term.
Applied high voltage of IDC (ODC) is +2.7kV (+2.6kV) to sense wires, -4.0kV (-4.5kV) to field wires and field shaper. Fig.3 shows equipatential map and electric field map of IDC. Electric field of IDC is 5.5 degree clined to drift direction to compensate Lorentz angle caused by magnetic field. We can see almost constant field strength all over drift region.
Not saturated Cool gas (CC>2 90% Ar 10%) is filled in all chambers including JET chamber. We use this mixture to make drift vclosity slow - about 7mm/p.s - and save the power of the read out clec'ronics at the expense of delicate control of high voltage and pressure of the gas.In ground operation , mass flow controller and gas mixer are used to produce mixed gas.Now we are studying scheme for maintaining the gas purity in as long as twenty hours during flight.
Electronics
Chamber signal is amplified with PREAMP whichi is mounted on the aluminum plate attatched to the endplate. We get 6 (5 for IDC) PREAMP output per sense wire, two is from both side of the sense wire and four is from two sets of the vernier pads (Fig.4). These signal are sent to various electronics and processed as shown in (Fig.5).
Track trigger system uses senswire signals of all chamber. At first, signals are amplified and discriminated with AMP/DISCRI cards. Then we get coincident signal of both inner and outer layer of each chamber.We call this signal is coincidence cell pattern which is consist of 23bit for IDC, 31 bit for ODC.This cell pattern are processed by NHIT module and translated into Nhit between 0-31 and encoded to 5bit hitpattem if Nhit=l From the Nhit and hitpattern data gathered four NHIT module, CHARGE module analyzes the momentum of incident track with 2MByte ROM look-up table and produce Level 2 trigger.
The timing and charge information of IDC vernier signal is processed by 33MHz Flash ADC system. PREA> IP signal from IDC vernier is amplified by 40 times and degitized to 8bit at each 30ns.for about 15p:s.COMPRESSOR then convert FADC data to timing , charge, first two data and other information to compress data size. We can calculate r ODC timing is given by 12bit TDC that convert time between TOF start signal and discriminated sense wire signal into 12bit digit. Vernier pad signal is converted to charge by charge sensitive ADC ADC convert integrated charge into 12bit digit. Gate for integration is given form discriminated sense wire signal. We can also use the charge of sense wire signal to decide coarse z position by charge division method. Now that electronics for charge division is not implimented, coarse z position is found by TOF time division. In future , z position can be calculated by ODC only. Performance Now we are testing IDC and ODC performance using cosmic ray, (3 source , and proton beam.We show some preliminary result of analysis of z position measurement. a) vernier pad We get charge of four vernier signals by integrating FADC data of cosmic ray events. The chage ratio £ of the outer strip and inner strip is linearly related to z position of the signaU'1 C_QA -QB QA + QB two set of e parameter are plotted in Fig.6(a). One side of the square is correspond to the quater of repeat distance.i.e.25mm. Applying cut in the shadowed region and projecting the data along the line in the figure , we can know aproximately resolutiion of z position. Fig.6(b) shows projection data converted to z position.The measuring resolution is 232nm rms. for cut data.Analisys of other part of data .especially in the round region near vertex of square is now in progress. b) charge division We put (3 source collimated with the aluminum bolock on the three different z position and measure the charge of both side of the sense wire by ADC. Measured position is Omm, 200mm, 400mm from center. Two charge is plotted in Fig.7(a). Each charge is describe with z position from the center of the chamber and the impedance of the sense wire Z^^nd the PRE A MP Zprcamp as follows. (0.5 - j-)Zwjre + Zpreamp Avire +2 Zpreamp (0.5 + —)Zwjre + Zpreamp Q2 = —L Q Zwire +2 Zpreamp So charge ratio S is given as a linear function of z. g _ Q2 - Qi ^ 2 Zwire z Q2 + Ql Zwire + Zpreamp L Charge ratio distribution at three points are shown in Fig.7(b) From this data, We can see that Zwirc = 2.25 Zpream[,. and z resolution is 11mm rms at L=400mm. ODC is able to determine z position about 10mm by charge division. Summary Drift chamber system for the track trigger and the precise position measurement has been constructed. Preliminary test shows that All chambers have good position resolution along z axis. Now we are analyzing data to decide the basic paramter - drift verocity , r -3r>- t • —5* lorentz angle etc. and are studying gas purification system and estimating effect of misallignment of the position of the chambers. reference [1] J. ALLISON et al.Nucl. Instr. and Meth. A236(1985)284 Fig.1 Schematic view of IDC and ODC -36- field wire honeycomb core 12mm 18 nm field shaping strip honeycomb core '125nmKAPTON sheet 18fim copper sheet 0.5 mm Aluminum sheet Fig.2 r<|) crossectional view field wire field wire (b) Fig.3 (a) Equipotential Map of IDC (b) Electrical field Map of IDC PREAMP vernier pad vf vernie sense wire Fig.4 Read out of the chamber signal with PREAMP IDCVERNIEF FADC system timing and charge of IDC FADC COMPRESSOR IDC SENSE AMP/DISCRT t COINCIDENCE' i NHIT CHARGE 2nd Level Trigger ODC SENSE TRACK TRIGGER system AMP/DISCRI COINCIDENCE' timing of ODC TDC ODC VERNIER CAMAC ADCfTDC system charge of ODC *• AMP/DISCRI ADC Fig.5 Data processing of the signal from IDC and ODC -0.6 -0.1 -0.2 0 0.2 0.* 0.6 (VERNlER3-VERNlt:R4)/(VERNieR3+VE«NIER4) VERNIER (a) -13.6 -13.2 -12.8 -12. 2 -11.6 -11.2 (b) Fig.6 (a) Plot of two e parameter (b) Resolution of vernier -•w- .-4000 c o 3200 •'•••-' • 400 BOO 1200 1600 2000 2400 2000 3200 J 600 4000 Ol (count) (a) (b) Fig. 7 (a) Plot of charge of both side of the sense wire (b) charge ratio at L=0mm,L=200mm,L=400mm -•!i- X •;4 U 3 *KP» The TOF system for BESS Mitsuaki Nozaki Faculty of Science, Kobe University Introduction The primary function of the scintillation counters which reside in the outermost part of the detector is to measure time-of-flight and charge magnitude of incoming particles and to generate trigger signals. The time-of-flight measurement distinguishes downward going anti-protons from upward going albedo protons. For a particle at light speed passing through the center of the detector, the time- of-flight will be 4.3 nsec. With an expected timing resolution of 0.2 nsec, the upward gonig particles are unambiguously identified. The mass determination is essential in anti-proton detection. The BESS experiment is equipped solely with a TOF system to reject negatively charged lower mass backgrounds such as electrons, muons, pions and kaons. Particle mass is given by the equation, m=ZeR(l/(32-l)1/2 .where Ze is the charge, R is the rigidity and |3 is the velocity. The transverse rigidity of an incoming particle and the sign of its charge are accurately measured by the jet chamber in an axial magnetic field produced by the superconducting solenoid.The total rigidity is then calculated using the directional information given by the IDC. The magnitude of the charge is determined from the pulse height measurement together with the velocity measurement. The energy loss in the counter for (anti)helium nuclei is 4 times as large as for (anti)protons. Thus the timing resolution determines the maximum momentum at which particles can be identified. A precise measurement of the hit position along the detector axis is necessary to determine the direction of the incident particle and to calculate the total momentum from the track curvature. The directional measurement is important in particular for gamma rays from point sources. The IDC vernier cathodes require a coarse position information to give an accurate axial coordinate. The coarse position information is provided by two methods. One is the charge division method using the jet chamber and the other is the time difference measurements given by the TOF counters. With an expected time resolution a hit coordinate along the counter will be determined with an accuracy of 3 cm. Design The TOF system consists of 16 plastic scintillators arranged cylindrically at a radius of 65 cm. They are grouped into 2 layers, 8 counters on top and 8 counters on bottom. The angular coverage of -45- ~* each layer is ±70° in phi and ±40° in theta. Each scintillation counter, 110 cm » 20 cm » 2 cm NE102A, is viewed on each end by a magnetic field resistant photomultiplier tube (Hamamatsu H261 ISX) through a adiabatically twisted acryl light guide. With a central field of 1 tesla, the PMT is operated in the ambient field of 1.8 KG without shielding. The field effect is minimum when the PMT is aligned to the magnetic field. The light guide is bent 60° at the end so that the angle between the PMT axis and the magnetic field is made as small as possible within the dimensional limitation. High voltage is applied to each PMT by an individual power supply which utilizes a air core transformer which suffers nothing from the mahnetic field. The output voltage is controlled manually. A gain monitor system using a laser light pulser (Hamamatsu PLP-02) is recently installed. The purpose of this system is to monitor the gain drift of the PMTs and to calibrate timing for each counter. Light output which has a wavelength of 410 nm generated as the second harmonics of the original infrared laser diode output is transmitted to each PMT through a 1 mm diameter plastic fiber. The pulse width is less than 50 psec and the the timing accuracy is less than 100 psec. Readout Electronics An anode output of each PMT is discriminated to provide a TDC stop signal. An 8 channel discriminator with high input impedance allows the input signal to be fed through to a ADC for pulse height measurement. Timing of the stop signal can be adjusted by a delay generator inside the discriminator module. The threshold can be set as low as 5 mV and has been set to 10 mV to minimize the time walk effect and to avoid spurious hit due to electronics noise. The CAMAC TDG with 8 input channels and 11 bit resolution is a modified version of LeCroy 2228A. Since the discriminator output has ECL level, the input stage of the TDC has been modified to ?ccept ECL inputs. The conversion gain of the TDC is 50 psec/count. The ADC which was developped at KEK has 16 inputs channels and 12 bit resolution. Its conversion gain is 0.6 pC/count. A delay line using an air core inductance to adjust the gate-signal timing and an attenuator to expand the dynamic range are inserted in front of the ADC. Dynode outputs are used to generate a level zero trigger. Signals from PMTs at both ends of a counter are lineary added before discrimination to reduce the effective threshold variation which arises from the position dependence of the pulse height The difference of the time of arrival at the analog sum is as large as 15 nsec depending on the hit position. The pulses are integrated with 20 nsec time constant in the analog sum circuit so that the pulse height can be added linearly. The discriminator provides 2 individual threshold levels which allows one to trigger for protons and helium nuclei separately. The discriminated signals are ORed inside the discriminator module and the outputs are sent to a trigger logic matrix. Charged particle trigger requires a coincidence between any one counter in the top layer and any one counter in the bottom layer. Gamma trigger requires only the hit in the bottom layer and null -Hi- Tf hit in the top layer since gamma rays are detected by the electron-positron pairs produced in the materials above the jet chamber. For the gamma rays the expected trigger rate is enormous and it must wait for the subsequent level one trigger generated using the hit information of the IDCs and ODCs. Performances The performance of the PMT itself and the readout electronics in the magnetic field has been studied using a spectrometer magnet at KEK (Ushiwaka) which can produce a strong field up to 1 tesla. Changes in the PMT gain and timing have been measured for various field intensities and inclination angles. In the actual operating condition, 1.8 KG and 15° tilt angle, the gain increased by about 10% and the timing deviates by 100 psec. Among the readout electronics the TDC was affected in the magnetic field and about 2.5% shift in the conversion gain was observed. It is because an oscillator inside the TDC uses an inductance which could not be replaced. It was found however the resolution was not degraded. There has been no effects in the other electronics modules. The performance of the TOF counters has been studied using the secondary beams extracted from the KEK proton synchrotron. The beam contains mainly pions and protons and the beam momentum was set to 1 GeV/c. The pulse height and the signal timing were measured for various hit positions. A rapid increase in the pulse amplitude near the PMT was observed. At the edge of the counter the change amounted to a factor 2. The light propagation velocity in the scintillator was measured to be 15.7 cm/nsec. The initial gain of the counter was adjusted so that the PMT gives 300 mV anode pulses for minimum ionizing particles. The corresponding dynode pulse height after added linearly is about 50 mV. Each counter gain has been calibrated by the I GeV/c n* beam and the subsequent drift or the change in the magnetic field is being monitored. This gain allows one to measure the energy loss up to 20 times as large as the minimum ionization which is expected for slow helium nulei. The relative timing of all counters was measured for the beams and for the laser light pulses. Any timing shift in the magnetic field can be corrected by the laser calibration with the magnet on. The accuracy of the time-of-flight measurement was estimated by the spread in the time difference, t(right)-t(left). The time resolution of the trigger counter was cancelled out. Although the pulse amplitude must be corrected for the timing, the preliminary analysis showed that the resolution of 200 psec can be achieved for the 1 GeV/c protons. Summary The TOF system has been constructed and its performance was studied using the test beam and the time resolution of about 200 psec was obtained. The effect of the magnetic field has been also studied. The laser system worked well for the gain calibration and the timing measurement. -•17- Particles IT ATOp Plastic scintillation TOF counters Fig. I r- xR n lighl"s TOFL-TOFR "Z. position 1 7 -» 2 Fi<*. 2 Z view of the TOF counters y. O Mechanical analysis for the BESS structure H. Yamaoka National Laboratory for High Energy Physics 1. INTRODUCTION The BESS structure undergoes stress during the launching and landing of the balloon carrying it, so we must ensure that the structure can withstand these large forces. The BESS boundary conditions for analysis as follows: - Horizontal acceleration structure force of 5G - Vertical acceleration structure force of 10G So that I analyzed structure by using the 'ANSYS program' Figure 1. shows the BESS structure configurations. The BESS detector is supported with the supporting structure which consists of a alminum frame and plywood stiffening panel. (1) Mechanical properties The mechanical properties of each material as follows. (Alminum) A6063-T5 Young's modulus 7300 kg/mm2 Poisson's ratio 0.3 Tensile strength 21 kg/mm2 Yield strength 16 kg/mm2 (Plywood) Bending Young's modulas 194-1117 kg/mm2 Compressive Young's modulus 103-666 kg/mm2 Bending strength 1.33 kg/mm2 Compressive strength 2.26 kg/mm2 (Nylon strap) Young's modulus 110 kg/mm2 Tensile strength 5.0 kg/mm2 The plywood has a different properties due to orthotopic material, so I used the minimum and maximum Young's module of the plywood for structural analysis. 2. STRUCTURAL ANALYSIS WITH A HORIZONTAL FORCE OF 5G (1) Approximate weight Weight 5G Scientific instrumentation 1500 kg 7500 kg NSBF equipment 600 kg Ballast 700 kg (2) Finite element model Finite element model shown in Fig.2.1 used the beam element and plate element. I fixed the one side of the BESS frame and placed half of the scientific package weight on the both ends of BESS detector in the horizontal direction. (3) The structural analysis When the plywood's bending Young's modulus changes from 194 to 1117 kg/mm2, the maximum stress changes from 3.5 to 2.9 kg/mm2 The maximum stress of the plywood changes from 0.57 to 0.86 kg/mm2. The BESS detector displaces along the horizontal direction by 0.11 -0.08 mm according to the plywood Young's modulus. Figures 4 and 5 show the stress contour display and displacement contour display with a horizontal force of 5G. 3. STRUCTURAL ANALYSIS AGAINST A VERTICAL FORCE OF 10G (1) Approximate load 10G Scientific instrumentation 1500 15000 kg NSBF equipment 600 6000 kg Ballast 700 7000 kg (2) Finite element model A finite element model is shown in Fig.3.1 used three element types;beam element, plate element and cable element. The cable element assumed the webbing strap which is 10 mm thickness and 100 mm width. I fixed the top of the webbing strapps and placed half of the scientific package weight on each horizontal face and distributed the NSBF equipment weight and ballast weight equally on the four bottom comers of the frame in vertical direction. (3) The structural analysis When the plywood's compressive Young's modulus change from 103 to 666 kg/mm2,the maximum stress became 5.7 to 5.0 kg/mm2. The maximum stress of the plywood became 0.78 to 0.83 kg/mm2 The maximum stress of the alminum frame became 6.5 to 6.2 kg/mm2 The BESS detector moved along the vertical direction by ~300mm. Figures 6 and 7 show the stress contour display and displacement contour display. (1) Stress [Horizontal 5G] Bending Young's modulus of the plywood 194 1117 kg/mm2 Stress in Alminum part 3.5 2.9 kg/mm2 Stress in Plywood part 0.57 0.86 kg/mm2 [Vertical 10G] Compressive Young's modulus of the plywood 103 666 kg/mm2 Stress in Alminum part 6.5 6.2 kg/mm2 Stress in Plywood part 0.78 0.83 kg/mm2 (2) Displacement [Horizontal 5G] ~0.1 mm [Vertical 10G] ~300mm (3) Tension in the webbing strap 7386 kg The both direction's maximum stress on the plywood became less than the maximum bending strength and also the maximum stress on the alminum became less than the yield strength. So that the present BESS structure will survive a horizontal force of 5G and a vertical force of 10G. -r>3- . • / . , ,• .• / ',' \ — — — -— — /' i ,• ; s s / ; > / j ; / > . Bess supporting frame ' s />>/,•>>.' s / / /' \ BESS \ detector / Alminum bar. •/•.'.•;,•'//, Plywood •2000 Fig. 1 The bess structure 1. Al-square pipe 2txl00xl00 2. Al-11 shaped bar 2. 5tx55x50 3. Al-channel 5tx100x50 4. Al-angle bar for fix the plywood 5. Plywood thickness=21mm 6. BESS detector le assumed the rigid cylinder Fig. 2 Finite element model for 5G analysis -r..i- 1. Al-square pipe 2txl00xl00 2. Al-II shaped bar 2. 5tx55x50 3. Al-channel 5txl00x50 4. Al-angle bar for fix the plywood 5. Plywood thickness=21mi 6. BESS detector We assuied the 3260 Vij rigid cylinder JZ&ofc; 72SOVJ 7. Webbing strap 10x100 Fig. 3 Finite element model for 10G analysis 194 1117 A 0.35 0.3 B 0.70 0.6 C 1.05 0.9 D 1.40 1.2 E 1.75 1.5 F 2.10 1.8 G 2.45 2.1 II 2.80 2.4 I 3.15 2.7 J 3.50 3.0 Ef : The bending Young's modulus of the plywood Fig. 4 Stress contour display for 5G analysis E 194 1117 A 0.02 0.016 B 0.04 0.032 C 0.06 0.048 D 0.08 0.064 E 0.10 0.080 Ere : The bending Young' s modulus of the plywood Fig. 5 Displacement contour display for 5G analysis 103 666 A 0.65 0.6 B 1.30 1.2 C 1.95 1.8 D 2.60 2.4 E 3.25 3.0 F 3.90 3.6 G 4.55 4.2 ][ 5.20 4.8 I 5.85 5.4 J 6.50 6.0 Ere : The compressive Young's modulus of the plywood Fig. 6 Stress contour display for 10G analysis Fig. 7 Displacement geometry for 10G analysis A Plenary Talk High Rate Data Acquisition Systems for Balloon Borne Experiments B. Kimbell, Particle Astrophysics Lab, NMSU Introduction There is no such thing as "the best" balloon data acquisition system. Each experiment has its own requirements and even these requirements change as the experiment evolves. Both BESS and the NMSU magnet experiment present challenging requirements in balloon telemetry. We have enjoyed and benefited from learning of the BESS system. In this same spirit we offer this overview of the NMSU system. Review of Balloon Telemetry Requirements and Options Options for Data Transmission Two options are available for transmitting payioad data to the ground: 1) using the NSBF CIP package, or 2) direct telemetry (TM). NSBF maintains and supports the CIP interface well, but the CIP is only available right before flight during field operations. The CIP data rate is normally limited to 32 Kbits/sec. Direct TM requires the user to provide and maintain their own payioad and ground transmitter and receiver hardware, but the interface is available at all times. The data rates available are in excess of 400 Kbits/sec, but ground data recording requires extra care at these high data rates. Options for Controlling the Experiment Two options are available for controlling the experiment: 1) using the NSBF CIP package, or 2) experimenter provided command system. NSBF maintains and supports the CIP interface well, but the CIP is only available right before flight during field operations. The NSBF system is awkward to use for direct ground-computer to payload- computer links. The user must provide and maintain their own payioad and ground command system interfaces, but use of the system while at "home" eliminates many possible integration problems when at the launch site. It is possible to make a command system that closely couples the ground and payioad computers. Options for Data Recording There are two basic approaches to data recording: 1) recording on-board the payioad, and 2) recording on the ground. The recent development of small, large capacity DAT drives has made it possible to record large amounts of data on the payioad. One then can use a lower downlink bit rate for just the engineering and science samples. However, care must be taken to ensure verification of the recording system prior to and during flight. It is difficult to ensure that the recording system is not a single-point failure for the flight. Recording all data on the ground eliminates the possible single point failure of the on board system, and it is easier to ascertain system functionality prior to and during flight. Recording all data on the ground requires a high downlink data rate and complete telemetry coverage during the flight. -61- The NMSU Data Acquisition System Overview Payload Data System The payload data system has evolved from a simple relay controlled operation in 1979 to a VAX 3200 system in 1992. The first computer controlled data acquisition system was a DEC PDP 11/2 which flew in 1986. We have continued to use DEC computers and Kinetic Systems CAMAC interfaces, upgrading almost every flight. The computer system is located on the baseplate of the payload, approximately 5 feet from the center of the magnet coil. The maximum magnetic field at this point is approximately 150 Gauss. The current VAX 3200 CPU is housed in a DEC Q-bus backplane with custom enclosure, fans, and power supply. The DEC disk drive is shielded with 1/16" steel, and uses the computer power supply (Figure 1.). PAYIOAD COMPUTER •CIELO' VAX 3200 z\CMD RCVR ENGINEERING "TfT MONITORS COMMAND DATA UPLINK DOWNLINK 149.62 MHz L-BAND 150 bpt 1.5155 QHz(IWI) 15eKbf» Figure 1. Payload Data System The disk drive holds the boot image of the DEC ELN real time operating system and execution code only - no data are written to the disk at any time. The executable code is loaded into memory after system boot, and then the disk drive is powered down. This saves power and ensures that a rotating disk is not subjected to the shock associated with launch, parachute deployment, or landing. The ELN system allows you to develop the execution code and customize the operating system on a host VAX, and download the compiled system to the payload computer over the LAN. The payload computer is part -62- of the PAL Local Area Network (LAN) when it is on the ground, and is disconnected from the LAN at the baseplate before flight. The VAX communicates with CAMAC crates #0 and #1 via Kinetic Systems 3922 crate controllers over a high speed parallel bus. CAMAC crate #2 is dedicated to drift chamber electronics, and communicates with CAMAC crate #1 via the LeCroy System 4290. NMSU Telemetry Links The radio frequencies available to balloon payloads are in the Lband, per international agreement. NSBF assigns specific frequencies within this band for individual flights. The allowed bandwidth in L band is the ultimate limit to the maximum downlink bit rate, approximately 400 Kbits/sec. NMSU has always used 156 Kbits/sec downlink, and it has been very reliable. We are in the process of upgrading to 312 Kbits/sec downlink rate to satisfy an ever increasing requirement for more data per event. NMSU provides and maintains all of our own TM hardware and software. Ail components are off-the-shelf, except for specialized CAMAC modules, which were designed and built in house. During ground testing the telemetry portion of the link is replaced by cables. The TM link is employed and tested as part of the preflight check out. Payload to Ground Downlink. All downlink frames are built in the payload VAX. The CAMAC 'FTMIO' module converts the parallel data to serial NRZ .Miller Code, and clock for transmission to the ground (Figure 2.). The CAMAC 'GTIM' module recombines the serial data and clock to form 16 bit parallel data. The GTIM module is fully programmable, and buffers the downlink data for the ground VAX. Ground to Payload Command Uplink. Each command frame is built in the VAX, encoded as a series of tone-shifts by the 'CMD Encoder' CAMAC module, and transmitted by a voice quality 60-watt transmitter to the payload. The CMD transmitter and receiver use FSK encoding via Hamtronics components. The command frame is converted from.serial to parallel in the CAMAC 'FTMIO' module, and sets a hardware flag to indicate to the VAX that a command is available. -63- P DATA DOWNLINK L-BAND t.5155 GHz (1881) ISSKbp. Figure 2. NMSU Telemetry Links The command system has worked well and proven capable of implementing very complex control requirements. There were some initial reliability problems that were resolved during ground operations. We have found that it is very beneficial to ALWAYS use the flight command hardware, even during ground testing. 47 words All data is organized into frames of 47 16- bit words. The first two words contain the frame synchronization words. The third word contains an identification number data which indicates the type of data contained in the frame (science, engineering, etc.). I words The last word is a 16-bit checksum. Figure 3. Telemetry Frame Format Tiroe- Engr. Sdence Event frame Science Event nnnn n nnnnn Figure 4. Organization of frames in the normal telemetry stream. The telemetry stream typically contains sets of 4-9 frames, (each representing a science event) with occasional isolated frames of engineering data or command replies (Figure 4.). In between frames the payload generates a pattern of alternating Is and Os to maintain synchronization. NMSU Ground Data System «track VT220 7XMB PAYLOAD DEVELOPMENT COMPUTER COMPUTER •CIELO- •CHAPC VAX 3200 VAX 4000-VLC CAM AC 5-10 PC WORKSTATIONS Figure 5. NMSU Ground Data System — 6fi — The ground LAN hosts VAXstations, microVAXs and numerous Personal Computers (PC). The VAXs are each dedicated to a specific task, as indicated Figure 5. The PCs are dedicated to individual users, and therefore serve many functions, such as CAD/CAM , data analysis, word processing, etc.. The LAN is Ethernet protocol with DEC Pathworks LAN software. A subset of downlink science data is saved in a continuous wrap file for real time science monitoring by any user on the LAN. Engineering data is continuously updated on color coded screens, and is also available to any user on the LAN. Command and control of the payload is limited to one computer, one console, and selected operators. Prime flight data is recorded on NSBF analog tape, and these tapes are digitized post flight by NMSU staff. We have had fidelity problems when digitizing these tapes in the past, so we now use a data verification process repeatedly during flight. Down Range Station Since we depend on ground recording of our data, we must maintain telemetry contact with the payload at all times. NSBF assures 300 nautical mile telemetry coverage from their fixed ground stations. For campaigns where it is probable that the payloads will drift out of telemetry range of the launch site NSBF will maintain a down range station to record data and monitor the balloon. NMSU collocates our down range DATA DOWNLINK telemetry equipment L-BAND 1.5155 QHz(lMI) with the NSBF 156 Kbp. mobile telemetry A V van. The NMSU COMMAND station monitors our UPUNK M»« MHj payload engineering 150 bp« and science data, and J*. CMO sends commands as NSBF TM VAN XMTH appropriate. The downrange COMMAND/ CMD station will be CONTROL ENCDR COMPUTER comprised of a PC and CAMAC crate interfaced to the phon* link to launch telemetry using the Figure 6. NMSU Down Range Station -m- same type of modules used at the launch site. The PC will be monitored via modem from the launch site using "remote" keyboard and display software. No NMSU personnel will be required at the downrange station during the flight. A simplified set of FORTRAN routines will be used to monitor and display the payload status. We don't expect to transmit actual science events from downrange to the launch site. The payload data will be recorded on analog tape at the down-range site by NSBF personnel. System Details Payload Software The payload software is written in Pascal and compiled with the operating system to form a bootable image which is downloaded onto the payload hard disk over the LAN. As shown in the flow chart (Figure 6), the payload program operates under programmed I/O - interrupts from modules are disabled. Spurious interrupts caused unrecoverable crashes in the initial computers, and interrupt I/O could lead to stack overflow and subsequent CPU crash in the VAX. ' Ir 1 i«fi No | «*»« 1 r 1 1* n tmt » gttiv tnpriMrlng Mta' |VM r—4 t* anfn—tht 1 No r I tt *•*• * Mtonot mnff Wit immiiiwii 1 r 1 I* t>«* • WttfnWy t am* *s NntfT |Y« r«M No 1 r Figure 7. Payload Software Flow Chart The rate at which engineering data is collected is selectable from the ground. The current rate is one complete update per second. The event trigger is disabled until the event data has been gathered. The science and engineering data are parsed into one large circular buffer. The telemetry output subroutine sends one frame from this buffer every time through this loop. The only exception to this is that command echoes are telemetered to the ground immediately after the command has been executed. While on the ground, the payload computer is a member of the LAN. This link is NOT used for data acquisition or for commanding the payload. It is only used to down-load and test developmental software. Once a software set has been tested it can then be —- —. , , - -t installed as the "boot file" for a hard disk located in the payload. Using this method, software changes can be implemented at any time up until the payload is carried to the launch pad. Command Protocol The data format for commands from the ground is the same as that for the frames transmitted from the payload. Each command frame contains a unique number which corresponds to a pre-established subroutine that actually performs the requested commands. The frame can also contain data relevant to the command ( for example, the command may be to change a voltage and the data would be the new value for that voltage). Commands can take many forms. Complex ones include "turn the payload on", or "ramp a series of ADC controlled voltages" or they can be simple relay closures etc. It is also possible to remotely execute individual CAMAC NAFs. Each frame is "echoed" back to the ground when it is received by the payload. The echo may also contain data from the payload. We also use 4 individual NSBF CIP commands. One command to discharge the magnet is a backup for the same command that can be issued by our own command system. This is the most critical command, and the CIP command ensures that we can discharge the magnet even if our command system has failed, or if the payload is out of telemetry range. Since the NMSU command system is implemented by the computer, it is necessary to use the independent CIP commands for battery and computer control during flight, if necessary. These 3 CIP commands are: 1) turn battery power off, 2) reboot the computer, and 3) turn the disk drive power on/off. In all cases, the NSBF CIP relay drives another NMSU relay circuit. Science Events Each cosmic ray trigger that occurs is subjected to on-board selection criteria. Events that pass the selection criteria are transmitted to the ground as 1-9 frames, each consisting of 47 sixteen-bit words. The number of frames is determined by the amount of data gathered for that event. The number of words per frame is fixed for each flight, but may vary between flights, as it is optimized based on the average number of words per event expected. One of the selection criteria is to NOT test the event before transmission to the ground. For example, every 100th event is NOT subjected to further selection criteria. The ratio of tested/untested events is software selectable by command. The current telemetry transmission rate of 156 Kbits/sec is the ultimate throttle on the total amount of data which can obtained from a flight of a given length. Therefore we always face the trade-off between : > overall number of events recorded, and > the total number of data words per event. This trade-off is optimized by: 1. Using command adjustable on-board software selection criteria to filter the events transmitted to the ground, 1i i I -Ii8- ~* 2. Using command selectable hardware trigger combinations to filter events, 3. Data compression techniques in the payload hardware and software. Future Plans Upgrade of on-board computers). Payload computer dead-time is a continuing problem - 30% dead-time is common. This dead time is a function of CPU capability and CAMAC bus speed. In 1992 the on-board micro VAX-II was upgraded to a micro VAX- Ill. We plan to further upgrade to VAX-4000 for next year. Multiple VAXs may be required in the future. Long term plans include incorporation of faster data buses as well. Use of on-board recording. When we began our work at NMSU the option of on-board recording was not available to us, so we were constrained to use ground recording. Today, with ever increasing data rate requirements, and the possibility of flying long duration flights out of normal telemetry range , we are considering on-board recording. We think that perhaps the best approach in the future is a system which allows BOTH forms of recording. Improvements to the TM-Output module in the pavload. To conserve VAX computing time, we are developing a TM output module that can format an event into frames by itself. This will save the on-board VAX from having to "parse" each event into frames. Command System Upgrade. By using modems operating in the payload and on the ground, we plan to command the on-board computer via its RS-232 serial port rather than through CAMAC. This will greatly simplify the command interface and software. -<»- Electronics and Data Acquisition System r - -* Progress of BESS Electronics Presented by ANRAKU Kazuaki Faculty of Science, University of Tokyo Hongo 7-3-1, Bunkyo-ku, Tokyo, 113 Japan from the Outer circumferential Drift Chambers (ODCs) and the Abstract Inner circumferential Drift Chambers (IDCs), the second level trigger logic (Tl) makes decision whether or not to send the New readout electronics for the BESS detector is described. event data to an Event Filter, which consists of a transputer- TAC type TDC modules for the chambers drift time bank. The Event Filter recognizes the jet chamber tracks and measurement. QVC type ADC nodules for signal charge discards unnecessary events. Only the event data passing the measurement and flash ADC modules for drift time and charge Event Filter are written to the storage device. measurement have been developed. Each module is equipped The data from each detector part are assembled and with hardwired zero suppression circuit to serve the fast data transferred by a transputer-network through its serial links and gathering. At the same lime, the modules are constructed to the capacity of the storage device is limited. Therefore the reduce power consumption. TAC and QVC circuits arc event data size reduction is crucial to improving the data optimized by a simulation program on a workstation. acquisition throughput rate and using the storage volume effectively. The trigger logic and the data acquisition system INTRODUCTION are described elsewhere in this proceedings. Since the BESS detector has a large geometrical factor for a READOUT ELECTRONICS OVERVIEW balloon or satellite borne detector, the first level trigger rate is high and the expected interesting events arc buried in a The schematic of the BESS electronics is shown in fig.1 . overwhelmingly larger number of background events. Photomullipliers anode signals of the TOF counters are fed to Furthermore the detector components are rather complicated 8 ch. Delay & Discri. modules and 16 ch. charge-to-voltage and the number of readout channels is large. Therefore the converter (QVC) type ADC modules. Delay & Discri. event data size tends to be so large that it is impossible to modules discriminate the signals and stop 8 ch. TDC transmit all the data to the ground or it might get beyond the individual channels after a prescribed delay lime for lime of data processing and recording capability of the data acquisition flight measurement. The ADC modules measure the energy system. loss of the incident charged particles in the scintillators. The first level trigger logic (TO) selects the events by the The jet chamber sense wire signals are amplified there and TOF counters information and starts data gathering if some sent to 16 ch. flash analog-to-digital converter (FADC) prescribed conditions are satisfied. Then using hit information modules. IDCs vernier pad signals are also amplified and read Local Arci Network ( Omninct ) D- r-«*UV 1—1 I N«—it W I ' Mlcroctmpultr CrBlr Mlcf Mompwltr Cratt CnuCwnllw TOF Caualtrt AD& TDC. ftapbftai - Drift Cfc««lMv« t :AMAC Crsi L'UCDIIM Fig. 1 Schematic of BESS electronics -73- by some of the FADC modules. IDCs sense wire signals arc A hitted channel selection and digitization take 4.5 usee. led {QAmp.lDiscri. cards. The discriminator outputs are fed to Total conversion time depends on the number of hits, which Coincidence Card for die Tl track trigger. causes a problem of estimating data gathering period. The ODCs vernier pad signals are amplified and fed to another performance of the module is as follows. type of 16 ch, ADC modules, caJled HC ADCs, which have individual gate inputs and hardwired zero suppression circuits. Dynamic range : 12 bits ODCs sense wire signals are, after discriminated by the Full scale : 8 usee Amp/Discri cards, distributed to gate inputs of the ADC Time resolution : 2 nsec modules, individual stops of the TAC modules and Integrated non-linearity: ±1 count Coincidence cards for the track trigger. Conversion time : 4.5 \iscc / hit channel TAC pan power consumption: 55 m W / channel CAMAC MODULES Module power consumption : 1.6 W. The TAC modules, TOF TDC modules and the two types Details of the TAC circuit are described in ref. [1]. of ADC modules are housed in two CAMAC crates together The TDC modules for the TOF counters are commercial with a crate controller with a transputer module mounted on it products. They are not equipped wiUi zero-suppression circuits , trigger logic modules. Coincidence cards and scaler modules. and consume rather much power. We also plan to develop a new TDC module to reduce power consumption and data TDC Module gathering time. [2] The TAC module is a single width CAMAC module with 16 channels of individual stop inputs. The TAC circuit of each channel is integrated on a subboard respectively, which is mounted on a CAMAC main board. A diagram of die TAC circuit is shown in fig. 2. A lime interval between Common Start and Signal Input is converted to the amount of charge in a hold capacitance CI by integrating a constant current from a current source composed of a transistor 04 and so on. The circuit was carefully designed to reduce the current of each part and Analog output temperature dependence widi die aid of a simulation program Analog Workbench (AWB)1*. A Block Diagram of the TAC module is shown in fig. 3. The module is equipped with a channel multiplexer and a 12- bit A/D converter. Signal Input to each channel in fig. 1 is latched and put to a priority encoder inputs as a Hit Output. After a certain time interval, the priority encoder selects only the stopped channels and the channel Analog Outputs are digitized in turn. After the digitization, its Hit Output is cleared and next hitted channel is selected by the priority encoder. The digitized 12-bit data are stored in output memories wim their 4-bit channel numbers. Fig. 3 TAC module block diagram ADC Modules There are two types of the ADC modules of CAMAC single width with 16-channel signal inputs, which are for TOF counters and ODC/TDCs respectively. Their QVC circuit parts are similar, but the HC ADC has a little more improved version of QVC circuits. Details of the QVC circuit for TOF ADCs arc described in ref. [1]. The QVC circuit diagram is shown in fig. 4. Signal Input current is integrated in a holding capacitance C3 white the complementary gates 1,2 are activated. The voltage on C3 is Fig. 2 TAC circuit diagram held while Reset input is low. The circuit is also optimized with AWB. The performance of the TOF ADC module is as follows. Dynamic range : ! 1 bits Full scale : 1200 pC Sensitivity : 0.6 pC Integrated non-linearity : ±1 count QVC power consumption : 80 mW / channel Module power consumption : 1.7 W. The TOF ADC modules are not equipped with zero-suppression circuits and, if necessary, can be replaced with HC ADC modules. HC ADC module is equipped with zero-suppression circuit and individual or common gate inputs. Two channels of QVC circuits are integrated on a subboard and eight subboards arc mounted on a CAMAC main board. The module receives both a common gate input and individual gate inputs, or only a common gate inpuL These two type gate modes are switched over by changing some jumper pins. A block diagram of a HC ADC module is given in Tig. 5. In the individual gale mode, a QVC Signal Input is integrated while bodi its Individual Gate and Common Gate arc activated. When Common Gate is disabled, the QVC Voltage Output is digitized by a 12-bit A/D converter, which is equipped on each channel, simultaneously with the other channels. After the digitization of 15 Usee, a micro-programmed sequencer scans the A/D converter 12-bit data buffers of all channels in turn and compares them with prescribed threshold values, which arc written to dedicated registers by a CAMAC command. Then the data smaller man the threshold is ignored and the greater data is stored widi its 4 bits channel number in successive addresses of output memories. The microsequencer operates at the frequency of 3.3 MHz and die channel scanning is completed within up to about 30 cycles. The output CAMAC Coairol Ejubla memories get ready to be accessed from the CAMAC bus within 25 |asec after die digitization Fig. 5 HC ADC module block diagram starts. This is much smaller than the digitization time of the TOF ADC module, which is always more than 70 usee, whereas A/D converters employed in HC ADC modules are much slower than those in TOF ADC modules. When the valid data are stored in the output memories a . LAM signal is asserted. A CAMAC accessing to the memories address where the valid data is stored issues a Q response. This enables fast data reading from the module. Details of HC ADC module will be described elsewhere. Crate Controller module New CAMAC crate controllers controlled by transputers Fig. 4 QVC circuit diagram on the board have been developed. These crate controllers ! J -75- communicate with each other and with the Event Builder, the jel chamber and IDCs sense wires are amplified and led to which resides on the FADC Crate Controller, through the inputs of FADC modules. FADC modules and FADC transputer serial links. Details of the module will be described crate follow the curocard spccificaiions wiUt 9U height (366.7 elsewhere. [4] mm), 280 mm width and 21 slots. Details of the system are described in ref. [3,2). FADC module Figure 7 is a diagram of one of 16-channeI FADC module. The input analog signal is digitized by a 8-bit flash A/D converter at the rale of 28.5 mcgasamplcs/scc (every 35 nscc). The digitized 8 bits data are fed to 8 bits address inputs of a 256 word x 1 bit SRAM, which is used as a threshold register. A bit sequence stored in the register is a scries of 0's from the address zero to an address equal to a prescribed threshold integer value, followed by a scries of I's up to the address 255. Therefore the register output bit becomes 1 only when the data is greater than the threshold. This output bit enables write enable inputs of the two FIFOs storing data and dicir time stamps. Thus data zero suppression is executed on a Fig.6 Schematic of FADC system real-lime basis. Sampling clocks of the flash A/D conveners and the other FADC SYSTEM timing clocks are generated by a clock and time stamp generator circuit on the Crate Controller, and they arc A schematic of FADC system is given in fig. 6. Up to 16 distributed on the lower FADC backplane to all FADC FADC modules arc housed in a FADC crate and each module modules. include 16 readout channels. One Data Compressor module and The module power consumption is as follows. (±6.8 V arc a Crate Controller arc also housed in the crate. Signals from nominal oulpul voltages of Li battery packs we use) T I-• [Threshold/Test data] . [Thf»i WE^I -[Ch Mitel 1*| [Pulse height data] -[FIFO RT»] -[FIFORSM "•inFOEF"! - (FIFO FT*) io\ [Time stamp dati] 3lo [Time stamp count] • |DftUn»wc«nl»lf) • icutn - ICLKJ] Fig. 7 One channel of 16 ch. FADC module FADC hackplanc KAlXTHKOi FADCFU'Oi FA DC module IPuU*h*lghld»U(f blU)J IRfirt] |Kmpirn»tl IKndfUgt [Time itimp (l« MU) 1 Si££Irf chinnel (1biui l lui channel fl«« ' ' | rcatiltr duller •H reeoRnlur clutter recognized (1»| channel leltclor ROM Sequence 4 (r*a titer dm compressor loc*I bus (16 bin) 2 clocki of different phuei Irtrupuicr d*U bui (16 bin) Fig. 8 Data Compressor block diagram +6.8 V : 2.8 A (standby) / 3.2 A (digilizaiion) -6.8 V : 0.15 A REFERENCES Total: 13.3 W (0.83 W / ch) (standby) 22.8 W (1.43 W / ch) (digitization). [I] S. lnaba et. al.. "Low Power TAC and QVC Circuits for Balloon Borne Experiments'*. IEEE Trans. Nucl. Set.. Vol. 37 No. 2, 1990. pp. 412-416. Data Compressor 12] Imori M. et. al. "Real-Time Data Processes in a Balloon-Borne Experiment", submitted* to IEEE Trans. Nucl. Sci. (June, 1992 Figure 8 shows a block diagram of Data Compressor. After issue). die digitization and zero suppression. Data Compressor scans [3] Anraku K. et. al., "A FADC System with Fast Data Compression for a Balloon-borne Experiment", submitted to ail FA DC channel FIFOs and converts ihc channel data to a IEEE Trans. Nucl. Sci. (June. 1992 issue). cluster sequence. A cluster is defined to be a set of data time 14} T. Sacki et. al., "Intelligent CAMAC Crate Controller with a stamps of which arc adjacent. The cluster sequence is Transputer ". to be submitted. composed of a cluster start lime stamp, first two raw pulse [5] M. Imori et. al., "Auxiliary Power Supplies Safety Turn on a height data, cluster total charge amount and cluster size. Baitery Powered System of Balloon Borne Experiments". Utyu-Kagaku-Kcnkyujo Houkoku Tokusyu Dai-24-gou Data flow is clocked and pipelined, where reading the (Special Issue on Balloon Borne Experiments from Institute channel data, searching the cluster, accumulating :hc charge of Space and Astronautical Science), Vol. 24, December amount and outputting the cluster sequence arc excepted in a 19S9. pp. /7-101. single clock cycle. Data Compressor operates at the frequency [6] Amaku K., Inaba S., Imon M. et. al., "Data Acquisition cf 15 MHz and the average data transfer rate from the channels System for Balloon Borne Experiments", IEEE Trans. Nucl. is more than 20 MBylcs/scc. Usually the data compression of Sci., Vol. 36 No. 5, Oct. 1989, pp. 1679-1684. 256 channels process takes less than 200 usee. Details of the (7] Imori M. et. al., "Modular Construction of a Balloon Borne Apparatus", Conference Record of the 1990 IEEE Nuclear Data Compressor are described in rcf. [3,2]. Science Symposium, Oct. 1990, Arlington, pp. 503-507. [8] Imon M, et al., "Incorporation of a Local Network Improves OTHER FEATURES Modularity of a Balloon Borne Apparatus", in submission. Other features of BESS electronics are described elsewhere, for example, in rcf. [2.4-8]. 78- -79- Progress of Data Acquisition System I.Ueda Department of Physics, University of Tokyo Hongo 7-3-1 Bunkyo Tokyo The BESS balloon-borne spectrometer has so a large volume and solid angle so as to detect cosmic ray particles of low flux. As a result, it produces a high-rate trigger due to background panicles. Also, the complex construction of the spectrometer and detailed tracking of the trajectory of incident particles performed by it provide large-sized event data. These conditions make two restrictions. One of them is the necessity of high-speed data acquisition. Transputers are introduced in the data acquisition system in order to realize high-speed processing of data acquisition. The other restriction is difficulty of transferring whole the data with telemetry system to ground-based stations to be recorded. For this reason, the data acquisition system includes data storage devices and store data into them. In order to store data of as many significant events as possible, it is necessary to suppress the total amount of data. One way to do this suppression is to reduce the size of each event data by squeezing significant information from each event data (data compression). The other is to reduce the number of events by squeezing significant events out of a large number of event data (on-line event rejection). Subsystem Network The data acquisition system is divided into four subsystems each of which has an independent function; communication with ground-based stations, monitoring of environment and detector status, event processing and data storage. This division provides some advantages that reduce complicacy and improve activity of each of the processes distributed among the subsystems. The subsystems are connected with a serial bus line cable and compose a local network (subsystem network) as shown in Figure 1. Commands for subsystems issued from a ground station are received by communication subsystem and then are transferred to the destined subsystem via the network line. Diagnostic informations or messages from the subsystems are sent to communication subsystem also via the network line to be transmitted to grand stations. In the individual subsystem an on-board microcomputer is installed to control the action of the subsystem and communicate with ground stations through the subsystem network. In each of communication subsystem and monitor subsystem NEC V40 (uPD7O208) LSI is installed as -81- -* a CPU of the on-board computer, and in each of event process subsystem and data storage subsystem NEC V50 (UPD70216) LSI is installed. The function of communication subsystem is to communicate with ground-based stations. The subsystem is to be connected to the NSBF telemetry and command system contained within the consolidated instrument package (CIP) in flight, or directly to ground-based stations in test working on the ground. Monitor subsystem samples periodically the output of sensors installed in the spectrometer and sends them via the subsystem network line to communication subsystem to be transmitted to ground stations, and also sends to data storage subsystem to be recorded into the storage devices. Event process subsystem gathers the digitized data from read out electronics, builds event data, applies some process to them and transfers the processed data to data storage subsystem. Event process subsystem and data storage subsystem are connected with a point-to-point communication line which specializes solely in transfer of event data and realizes high speed data transfer. Event data are transferred to the data storage subsystem via not the subsystem network line but this special data transfer line for the sake of high rate data gathering. The data transfer line is realized with transputer links which are referred later in the next section. Occasionally event data are also transferred to communication subsystem via the subsystem network line to be transmitted so as to provide real time information upon the events being acquired and recorded. Transputer Network Processes to deal with event data are required to be performed at high speed due to the high frequency of triggers and the large amount of data of each event. A certain number of INMOS transputers are introduced both into event process subsystem and data storage subsystem to accomplish high speed data acquisition. The transputers installed in the two subsystems are connected one another via serial links and construct a transputer network as shown in Figure 2. The serial links included in transputers provide point-' >- point communication and a transputer network is easily constructed by means of them. Since the communication between two transputers is performed with point-to-point serial link, they need not reside in one crate together. Processes for event data acquisition are distributed among the transputers and progress in parallel. Event data acquisition is performed in three steps; event building process, event filtering process and data storage process, which are pipe-lined so as to improve the response to the high rate trigger. Event Building Process Read-out electronics to digitize the information of signals produced by the spectrometer are installed in three crates. The modules which include FADCs are installed in a custom-made crate (FADC Crate), and the modules which include ADCs and which -82- include TDCs are installed in two CAMAC crates specially modified for the BESS experiment (CAMAC Crates). A transputer is installed in the crate controller of the each crate, so FADC Crate Controller and CAMAC Crate Controllers are intelligent modules which can be programmed and control the each crate by themselves. Event Builder exists as a process programmed in the transputer installed in FADC Crate Controller, and start data acquisition by issuing an order to the crate controllers to get ready. A trigger signal can be produced after that and activate read-out electronics, which causes crate controllers to start data gathering. The data gathered by the crate controllers are transferred to Event Builder to be combined into an event data. Tne data from CAMAC Crate Controllers are transferred via the transputer links at a transfer rate of 20Mbps. The transfers of the data from FADC Crate Controller, on the other hand, are performed as a memory block move by the transputer at a transfer rate of some 20 Mbytes per second, which is necessary because of the large amount of FADC data produced out of the signals of the tracking device in the spectrometer. Event Builder has three buffers for event data, and three serial links for output of event data corresponding to each of the buffers. Then, transfers of three event data from Event Builder can be performed at the same time using these buffers and links, and also at the same time with the data gathering and event building process so as to keep the event building rate high. Event Filtering Process Since the event filtering process is now in development, the design of the Event Filter Bank is to be described here. The event data built in Event Builder are fed into Event Filter Bank which is composed of a certain number of transputers. The event filtering process is to be performed in each of the transputers and is to realize an on-line event rejection. An event data fed into Event Filter Bank is to be input to one of free transputers in the bank and examined there to be selected or abandoned. In this way, as many event data can be processed in Event Filter Bank as the transputers exist in the bank. Since the process is in development now, there are only three transputers in Event Filter Bank at present. In the no distant future plan, nine or twelve transputers will be installed there. Data Storage Process The data selected by the event filtering process are transferred from Event Filter Bank to the transputer installed as a storage device driver in data storage subsystem. This transfer is performed via only one transputer link, which is sufficient for the selected event data because of the reduction of the event data in number or event rate. Two EXABYTE 8mm cartridge tape data recorders are introduced as the data storage devices. Each of them being able to store data up to some 5 Gbytes, it is possible to store data up -KS- to about 10 Gbytcs in a flight. EXABYTE 8mm cartridge tape data recorder is a device based upon Small Computer System Interface (SCSI) standard and the data transfer from the storage device driver to the device is performed by SCSI controllers installed in both side. Data storage subsystem receives not only event data from event process subsystem, but also monitor data from monitor subsystem. The monitor data are transferred via the subsystem network line and received at first by the microcomputer which faces the subsystem network, then transferred to the storage device driver to be recorded into the devices. The storage device driver packs both event data and monitor data into blocks with fixed length before storing them into the devices to use their capacity efficiently. Summary The high speed data acquisition system using transputers is developed and under examination. It performs high rate data acquisition of some 1000 events per second (peak) for events which data size is about 500 bytes, and stores the data into EXABYTE 8mm cartridge tape data recorders. Event Filter Bank is now in development and some hopeful results are achieved in preliminary tests, and it is planned to reduce the rate of events to be stored down to some 200 events per seconds. Taking in the typical data size of about 500 bytes, it takes about 20 hours for the storage devices to be filled, which is long enough for the one-day flight scheduled for this summer in Canada. -XI- ^ Monitor Subsystem Communication Local Area Network Subsystem Subsystem Subs; -tern Conductor (Omninet) Conductor Monitor Event Process Data Storage Module Subsystem Subsystem Subsystem Subsystem Conductor Conductor Detecter Readout Storage Device and Driver Event Process Data Storage Device Figure 1. The subsystem network constructed in the BESS data acquisition system. Event Process Subsystem Data Storage Subsystem to Data Storage Conductor to Event Process Conductor Boot-strap ROM Event Event Event Filler Filler Filter Storage Boo(-5(l3p Even! Event Event Event Data Filter Multiplexor Device ROM FADC Crate Filler Filter Driver Controller Event Event Event SCSII/F Filler Filler Filter Module CAMAC CAMAC Crate Crate Controller Controller Z\ SCSI CAMAC Bus CAMAC FADC Event Filter Bank Crate Crate Crate Storage Devices Figure 2. The transputer network constructed in the BESS data acquisition system. Progress of the BESS Trigger System Takayuki Saeki Faculty of Science, University of Tokyo Trigger Logics of BESS Detector How charged particles and gammar rays pass through the BESS detector are shown in figure 1. The right figure is for charged panicles and the left is for gammar rays. An incident charged panicle hits the top TOF counter, the upper outer cylindrical drift chamber(here after called ODC), the upper inner cylindrical drift chamber(here after called IDC), the lower IDC, the lower ODC and the bottom TOF counter. It also leaves a track with negative or positive curvature according to its sign of charge in the jet chamber. In the case of gammar rays, there are no hits at the top TOF counter and the upper ODC and it converts into a pair of an electron and a positron in the supper conducting solenoid. The electron and positron hit the upper IDC, the lower fDC, the lower ODC and the bottom TOF counter. They leaves two tracks in the jet chamber. The trigger logics of BESS detector is shown in table 1. It is divided into three stages, that is, TOF trigger logics, master trigger logics including track trigger logics and on line software trigger logics. TOF trigger logics and track trigger logics are implemented by hardware and they are so-called TO trigger and Tl trigger respectively. On line software trigger is realized by a transputer network. In the stage of TO trigger, anti-proton like particle, anti-helium like particle and gammar ray are distinguished by the deposited energy and the hit pattern of TOF counter. Anti-heliums deposit larger energy than anti-protons. And gammar rays don't have hits in the top TOF counter and the upper ODC outside the solenoid. In the stage of Tl trigger, decisions of the TOF trigger and the track trigger are combined. The track trigger watches curvature of a track through cell hit pattern of cylindrical drift chambers. If there is only one hit cell in each layer of the cylindrical chambers, the range of curvature is known from the configuration of those four cells. If it has clearly positive curvature, that means it is a proton, a helium or something with positive charge, the event is rejected by the master trigger. In the stage of the on line software trigger, the track in the jet chamber is analyzed taken account the decision of master trigger. For the event triggered by an ami-charged like particle, consistency with the hit positions of the IDCs, ODCs and the track in the jet chamber are confirmed and the curvature of the track in the jet chamber is checked again. If it has positive curvature, the event is rejected. For the event triggered by gammar ray, consistency with the hit positions of the IDCs, the ODC and die tracks in the jet chamber is confirmed. Implementation Electronics of TOF trigger The electronics of TOF trigger is shown in figure 2. Each plastic sintilator of TOF counter has two PMTs at the both ends. The two dynode signals are added and fed to the two-level discriminator module. The diagram of the two-level discriminator madule is also shown in the figure. It has eight channels and you can set two thresholds, higher and lower, to each channel. The higher threshold is for anti-heliums and the lower is for anti-protons. Eight discriminated signals from the eight channels are ORed for higher and lower threshold respectively and the results are output to two gate signals. There are two two-level discriminator modules in the system. One is for the top TOF counter and the other is for the bottom. Those four output gate signals are fed to the TOF trigger module which issues TO gate signal if any conditions shown in table 1 are satisfied. The TO gate signal starts up all TDC, ADC and FADC modules. Electronics of Track trigger The electronics of the track trigger is shown in figure 3. Discriminated signals of all sense wires of the IDCs and the ODCs are fed to four coincidence cards, each of which makes coincidence of gate signals of two adjacent sense wires and output cell hit pattern. The N-hit modules decode the cell hit pattern into 20 bits digital value. The charge decision module makes decision of the curvature by the 20 bin. address input and 8 bits data output ROM, and 0'itpuis the result to the master trigger module. The master trigger module inputs signals from TOF trigger module and the charge decision module and outputs Tl trigger signal following the logics shown in table 1. Time Chart of Triggers The time chart of the triggers is shown in figure 4 and 5. With the TO trigger signal, all modules start data conversion as mentioned before. The decition of Tl trigger is made within 15 micro seconds after TO trigger. If it is 'reject', all modules except for the FADC modules are fast cleared by hardware. FADC modules are fast cleared within 50 micro seconds by software and then all trigger modules are cleared. In this case the system becomes ready for the next TO trigger within 80 micro seconds. The time chart of the triggers in the case of Tl 'accept' is shown in figure 5. It shows the data conversion time of each module. The configuration of the network of transputers is shown in figure 6. The transputer in the event builder reads data from the two CAMAC crate controllers and the FADC data compresser circuit. It packs the data in a format and sends to the transputer bank for on line software trigger. Once the data is sent to the transputer bank, the system can be ready for the next TO trigger. The duration between TO trigger and the next TO trigger enebled time is about 1 micro second for a typical event. On Line Software Trigger Through the transputer bank, event data are processed and the track may be recognized. The track finding is done in each cell of the jet chamber, whose configuration is shown in figure 7. Each of the cell includes four sense wires and its horizontal dimension equals twofold full drift length. Firstly tracks are recognized in each cell and are assumed to be lines with no curvature approximately. Right and left ambiguity can be solved in each cell due to the 500 micro meters staggered configuration of adjacent wires. The track which is recognized in a cell is called a track segment here after. Secondly the recognized track segments should be connected and combined to be a track passing through the jet chamber. For this purpose, two track segments in different layers are choosen. If the two track segments belong to a same track, the crossing point of the two lines, each of which perpendicularly bisects each track segment, may be the center of curvature. If it is, the distances from the crossing point to two track segments are same. And if not, the distances are different. So you can find a true combination of track segments which reconstructs a track through the jet chamber. In addition to above argorithm, another argorithm is used complementary. If you plot vertical position(Y) of the track segment vesus sine theta(sine), where theta is zenith angle of the track segment, those plots can be fitted by a line as shown in figure 8. The inclination of - KX -- f the line is equal to the radius of the curvature and the interception of the Y axis is the Y coordinate of the center of curvature. But in this argorithm it is difficult to distinguish two tracks with almost same curvature because it neglects the horizontal coordinate. So this is only used to obtain the value of curvature for plots given by the first argorithm. A result of processing is shown in figure 9. The speed of processing a typical event is about 100 events per second per transputer. We intend to use 9 or 12 transputers for this processing to realize processing speed of 1000 events per second. Summary BESS detector may be triggered in the stage of TO at the rate of 3 ~ 5 KHz. Clearly distinguished proton events are rejected by Tl trigger and the rate becomes about 300 - 500 Hz. Those events are sent to the transputer bank and the tracks in the jet chamber are recognized to get the curvature more precisely. If the cuvature turned out to be positive, those events are rejected and the rale becomes 100 - 200 Hz. Passed events are recorded in the 8 mm video tapes whose capacity is 10 GBytes. This means that BESS detector can be operated continuously during 20 hours flight. So the result is that: the number of TO triggered events may be about 10^ and the number of recorded events including data of the jet chamber may be about 10^. -• Si) -- anti-p anti-He gammer TOF top Low-th o X Hi-th 0 TOF bottom Low-th 0 o Hi-th o N-hit ODCup 1 1 X IDC up 1 1 1 IDC down 1 1 2 ODC down 1 1 2 track trigger negative negative cell hit pattern of (IDC/ODC) curvature curvature gammer negative curvature negative curvature traking in JET and and consistent track consistent track consistent track Table 1. Trigger logics of BESS detector Figure I. How particles hit BESS dciecior ? -<= r^iiiMbtodADO ) CAMACmodula ? 3 | PMT dacrunimKr with lu^ ttiMbdd • owpwli fnWpr mtorwkl Figure 2. Electronics of TOF trigger CAMAC module coincideced 31 gale signals from coincidence 30 gate signals N-hit N-hits(5bils), the hit cell no.(5biis) upper ODC electronics > card encode CAMAC module CAMAC module VMF. module coincidcnc<;d 31 gate signals from coincidence 30 gate signals N-hit lower OUC electronics UMBEI card encode decision to charge master trigger decision module(8bils) CAMAC module coincidcnccd 23 gale signals from coincidence 22 gate signals N-hit upper IOC electronics card encode VM'i module^ coincidcnccd CAMACm0duie 23 gale signals from coincidence 22 gate signals N-hit lnwer IDC electronics card encode TOF trigger Track trigger 4 bits 8 bits master trigger module CAMAC module Tl decision(accept or reject) Figure 3. Electronics of master trigger and track trigger Hardware Software TOF trigger (transputers) Hardware Software TOF counter ODC IDC/JET (transputers) TOF trigger TDC ADC FADC start H gate sran f~bpm. sate start TOF counter IDC/JET TDC ADC TDC stan gate start j-fcom. gate )-j start Track Trigger Dy the hit-patiem or' conv. [DC and ODC end TO delayed 18 usee interrupt Read Tl dccition conv. conv. Track Trigger end end ay the hit-pattern of |20- 30^Lsec [DC and ODC accepted 30|isec conv. conv. end end ,100 usee lOOjisec accepted TO delayed interrupt Fast clear by hardware Read Tl decition data comp read "* lS^isec CAMAC rejected 200[isec modules fast clear FADC by software modules clear rejected pack data Track trigger modules in a format -80 usee send the packed data to the transputer bank Figure 4. Tl rejected case. clear all modules and becomes ready for next trigger J—J Figure 5. Tl accepted case CAMAC crate controller I CAMAC craie controller 2 CAMAC modules - CAMAC modules _ ^ data - S data 0 MndukJDLlcpt Sense Wire Plain SflashROM cross flow command transputer V50interfacel transmitter M © jiinaxhuJdcr FADCI/F __ _ ^ compressor data _ „ _^. 1 T2 event selection transputer network buffering buffering SCSI &SCS1 . — _»- two 8mm video command tape recorder •S 4 Sense Wires full drift V50intcrface2 nashROM Q ModuJe for boot Figure 6. Configuraiion of transputer network Figure 7. Configuration of cells I -i-^^i-; —H>- si r\e Q iiicliiiiilion = radius of curvature intercept of Y = Y coordinate of center of curvature Figure 8. Algorithm of track finding particle particle \ X raw tint a processed dala Figure 9. Result of processing Examination of Multi-track Triggers R. Golden Introduction: In this talk we will look at the various types of triggers encountered during a typical balloon flight. The data presented here were gathered during the flight of the NMSU balloon borne magnet system on Sept. 23-24, 1991. The balloon flight took place from Ft. Sumner, New Mexico. Figure 1 contains a drawing of the instrument. The drawing is not quite accurate in that the tracking system also included 20 planes of drift chambers. Figure 2 shows a typical event. The circles in the tracking region are radii corresponding to the drift time measured in each drift cell. The text at the bottom of the figure indicates 1/rigidity (labeled "def") which is, in this case, -0.18 corresponding to a negatively charged particle with a rigidity of 5.6 GV. The next lower line indicates the pulse-heights measured by the 4 phototubes located in the Cherenkov detector. Note that 3 are basically pedestal values whereas the fourth (reading 223) definitely indicates the presence of Cherenkov light. Note that the imaging calorimeter clearly indicates a cascade starting at or near the top. Discussion of the Method: Using the "VIEW" utility in our data analysis programs, we Cerenkov looked at 50 triggers which were taken when the "track selection" criteria were being applied by the on-board computer. These criteria required that at least one of the top MWPC be fired and one of the bottom MWPC were fired. These fifty triggers were then counted in one of 8 possible categories. This process was repeated for 50 Calorimeter triggers taken when the "track selection" criteria were disabled. A notebook was made with hard copies of most of the events used in this study. The notebook can Figure 1. The MASS2 Instrument be obtained from Dr. A. Yamamoto. -34 h 5358 * -11 h -27 h EV« 41623 DEF.CX.CY = -B. 18 23.3 0.3 NX, NV, I'll ,NS =73 83 3isder=0.006 G values = 223 16 15 13 NSING, NMULT CX,Y>= 0,0211,0514.0 45.0 enter FClnished). XVCylewJi CChlwlew), SC howew )i TCop ), R< ef it >i DCunp), PC rmt) > Figure 2. A "View" representation of a Typical Event Table 1. Summary of the Observations event characterization sample (almost) random multiple, single, interactfo multiple. good track, good track, TOTAL blank trash large large n in wall In low en primary SAMPLE anale ano.le .flejmew, * . _ 4 <; « 3 ..7 , K 17 Wl rtrts nft A 7 q 1? 4 ., ,1 ft 7 ,., nn Figure 3. Summary of Results. The results are shown normalized to 1 normal primary cosmic ray. Results: The results are summarized in Table 1 and Figure 3. The statistics are extremely limited but some clear trends are easily seen. For the case when the track selection test is enabled, about 1/3 of the triggers are normal primary cosmic rays. With the track selection criteria disabled, only 1/7 of the triggers are primary cosmic rays. The difference in these samples is due in part to the fact that the geometry defined by the trigger detectors is somewhat larger that the geometry of the tracking system. It should be noted that these ratios are undoubtedly dependant on the experiment configuration. It is hard to estimate how to infer one experiments performance from that of another. The real value of this w. •» is probably just to indicate that many of the triggers appear to be due to VERY low energy multiple-track events. These probably result from interactions of cosmic rays with payload materials located outside the trigger geometry. - !W - Technologies for Future Projects February, 1992 Track Trigger Using Neural Network K.Taruma Graduate School of Science and Technology, Kobe University Nada, Kobe 657, JAPAN Abstract: Neural network technique was applied to identification of track charge in BESS detector, and its performance was studied. Optimizing network parameters using back propagation learning mechanism, the charge of lGeV/c particles was determined with almost 100% and more than 93% accuracy on the condition that detector noise is 0% and 5% respectively. Taking account of its simple and fast processing ability, neural network method can be one of new approaches to fast on line trigger. The 3rd workshop on Balloon-Borne Experiment with a Superconducting Spectrometer February 24-25.KEK National Laboratory for High Energy Physics -Mi- I. Introduction Neural network is constructed from large numbers of simple processors called neurons which are highly interconnected each other. Artificial neural network has some of characteristics of human brain, in particular fast pattern recognition in presence of noise. Several applications of neural network to high energy physics have been reported, and very successful results have been presented! 1], for example, identification of the ancestor of hadron jet, discrimination between b-quark and light quarks, fast track finding etc. Since charge identification of panicles detected in magnetic field is just equivalent to the pattern recognition problem of which neural network has an advantage, neural network technique was applied to charge identifier of BESS detector. This talk initially presents the brief introduction to neural network. And the method of application to charge identification and some results are given. i 2. Network basis Feed forward network was used for identification of track charge. Figure 1 shows the architecture of feed forward network which consists of input(I), hidden(H) and output(0) layer. Each node gets weighted sum of output values from all neurons of upstream layer and gives output values accordingly with the nonlinear neuron transfer function g(x). Output value O- is given by C; = g( Iwj *(Swj*/*+ey)+ftj where the weights(tv,J and the threshold values(£?) are the parameters to be fitted to the data distributions. Vvix g{x), sigmoid function -mi- • Pi i-e- 1 P i is minimized by gradient descent method. The details of back propagation rule is described in reference 2. 3. Training and results The simple simulator of BESS detector was used to generate the tracks. The simulator includes only ODC and IDC in magnetic field. ODC and IDC consists of 32(up)+32(down) and 25(up)+25(down) cells respectively. Track comes in one of 6 center cells of up-ODC and its incidence angle is restricted within +/- 15 degrees. Efficiency and noise level of detector cells can be changed. The momentum of particle is also changeable. Magnetic field was fixed at 1.2 tesla in this study. The simulator gives the set of hit cell number for each track. Three layered feed forward network with 104 input nodes, 10 hidden nodes and an output node was used. Each input node corresponds to one of detector cells, and 1 is set to the nodes of hit cells and 0 is set to other nodes. The output node gives calculated values between 0 and 1. This value was compared with aimed code value of particle charge; 0 for negative particle and 1 for positive particles. Training and test were done using JETNET2.0[3] developed by LUND group. Temperature(7") of neuron transfer function was set to 1. The weights and threshold values were initialized at random within +/- 0.1. The step size of weight was set to 0.01. Generated tracks which contains both charge randomly at equal probability were used for training. Figure 2(a) shows the fraction of correctly classified tracks for lGeV/c particles plotted against number of tracks used for training. If the output value is greater/less than 0.5 then it is counted as positive/negative charge. Figure 2(b) illustrates the output distributions on several steps of training. Output values for negative and positive particles are separating each other with the progress of training. Training was continued till the fraction of correctly classified tracks were saturated. At least 1,000,000 tracks were used for training. After training, network performance was studied using independently generated 5,000 tracks. Figure 3 shows the fraction of correctly classified tracks plotted against (a)momentum of particles at efficiency and noise are 100% and 0% respectively, (b)detector noise and (c)efficiency. Figure (b) and (c) are results on lGeV/c particles. The charge of lGeV/c particles was determined with almost 100% and more than 93% accuracy on the condition that detector noise is 0% and 5% respectively. The performance -nir,- of the network less depends on detection efficiency. Figure 4(a) shows the final output distribution for 3GeV/c particles. From this data, negative particle detection efficiency versus positive particle contamination can be calculated and the result is shown in figure 4(b). The positive particle contaminalion less lhan 20% was achieved at negative particle detection efficiency of 90% for 3 GeV/c tracks. 4. Summary and outlook The basic performances of charge identifier using neural network with back propagation method were studied for BESS experiment. The fraction of correctly classified tracks versus momentum of particles, efficiency and noise of detector cells were presented. An example of positive particle contamination versus negative particle detection efficiency was also given. As this study has just started, there is a lot of works which should be done before realistic triggering system fitted for BESS experiment is developed. The performances of neural network should be checked more precisely, for example, the behavior when two tracks come in the detector, the possibilities to improve performances by use of position information in the hit cell instead of hit cell number and by use of additional TOF information etc. It is important to know the variation of network performances caused by the fluctuation of parameters in case of making the network circuit. It is scheduled that more sophisticated simulator such as GEANT and/or real data are used for these study. Since the neural network technique can be effective method to fast on-line trigger, the study on hardware also has been started. References [1] B. Denbyetal., "Spatialpattern recognition in a high energy particle detector using a neural network algorithm", FSU-SCRI-89-79. C.S. Lindsey et al., "Primary Vertex Finding in Proton-Antiproton Events with a Neural Network Simulation", FERMILAB-Pub-90/192, Submitted to Nucl. Instrum. Methods A. B. Denby et al., "Status of HEP Neural NET Research in U.SA.", FERMILAB-Conf- 90/21, The 1989 Conference on Computing in High Energy Physics, Oxford, England, 1989. G.S-Abele et al., "Fast Track Finding with Neural Nets",UAB-LFAE 90-06, Submitted to Computer Physics Communications. L. Lonnblad et al, "Finding Gluon Jets with Neural Trigger", Phys. Rev. Lett. 65,1321(1990). C. Peterson, "Neural Networks and High Energy Physics", LU-TP 90-6, International Workshop on Software Engineering, Artificial Intelligence and Expert Systems for High Energy and Nuclear Physics, Lyon, France, 1990. L. Lonnblad et al, "Using Neural Networks to Identify Jets", LU TP 90-8, Submitted to Nuclear Physics B. P. Bliat et a!., "Using Neural Networks to Identify Jets in Hadron-Hadron Collisions", ISSN 0418-9833, the proceedings of the 1990 Summer Study on High Energy Physics Research Directions for the Decade, Snowmass, Colorado, 1990. C. Peterson, "Neural Networks in Particle Physics", LU TP 91-20, Workshop on Neural Nettvorks: From Biology to High energy Physics, Elba, Italy, 1991. L. Bellantoni et al., "Using Neural Networks with Jet Shapes to Identify b Jets in e'e Interaction", CERN-PPE/91/80, Submitted to Nucl. Instrum. and Method A. D. E. Rumelliart et al., "Parallel Distributed Processing, Explorations in the Microstructure of Cognition", Vol.1, ch 8, MIT Press, Cambridge, Mass. L. Lonnblad et al., "Pattern Recognition in High Energy Physics with Artificial Neural Networks -JETNET 2.0", LU TP 91-18, Submitted to Computer Physics Communications. Input(Ik) Hidden(Hj) Output(Oi) Target(ti) [Aimed output] Figure 1. Feed forward neural network with input;!) hidden(H) and output (O) layer. And a neuron processor. - 1"N-- i—i i 11 mi 1—i i i mil (a) J i i 11 nil -I I I I I III! I I I I I III 104 105 10« # Tracks 3000 (1) 2000 1000 w 2000 2 I 1500 In < > £ 1000 =a= 500 ... .Ink ... 1000 (3) 750 500 - •L 250 - 0 0.5 10 0.5 1 Output values Output values Figure 2. (a)Network performance as a function of number of tracks used for training. (b)Output distributions for positive(thin line) and negative(bold line) particles on several steps of training. (1) for 1,000 tracks, (2) for 3,000 tracks (3) for 5,000 tracks, (4) for 7,000 tracks, (5) for 10,000 tracks and(6) for 80,000 tracks. - low- 100 - D 90 (a) 80 70 60 1 I I I 0 0 2 4 6 8 10 Momentum (Gev/c) £1 o 100 u ^ n D 95 — D (b) OT CO 90 *o 85 u on 1 1 i u 1 1 i o o 0 0.02 0.04 0.06 0.08 0.1 Noise level of detector cells o CO u 100 B a D 95 — (c) 90 85 an 1 i 1 1 1 0.98 0.96 0.94 Efficiency of detector cells ure 3. Network performances plotted against (a)momentum of particles at efficiency and noise are 100% and 0% respectively, (b)detector noise and (c) efficiency for lGeV/c particles. -llo- Distribution of output value P=3(GeV/c) Eff=1.0 Noize=0.0 (a) 3000 ^2000 o 0 0.2 0.4 0.6 0.8