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Astrofisica Gamma

Astrofisica Gamma. EGRET AGILE GLAST. Energy loss mechanisms:. . Pair-Conversion Telescope. anticoincidence shield. conversion foil. particle tracking detectors. e –. calorimeter (energy measurement). e +. Experimental Technique.

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Astrofisica Gamma

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  1. Astrofisica Gamma EGRET AGILE GLAST

  2. Energy loss mechanisms:  Pair-Conversion Telescope anticoincidence shield conversion foil particle tracking detectors e– • calorimeter • (energy measurement) e+ Experimental Technique • Instrument must measure the direction, energy, and arrivaltime of high • energy photons (from approximately 20 MeV to greater than 300 GeV): • - photon interactions with matter in GLAST • energy range dominated by pair conversion: • determinephoton direction • clear signature for background rejection - limitations on angular resolution (PSF) low E: multiple scattering => many thin layers high E: hit precision & lever arm • must detect -rays with high efficiency and reject the much larger (~104:1) flux of background cosmic-rays, etc.; • energy resolution requires calorimeter of sufficient depth to measure buildup of the EM shower. Segmentation useful for resolution and background rejection. Astrofisica Gamma

  3. Science Drivers on Instrument Design  e– e+ Background rejection requirements drive the ACD design (and influence the calorimeter and tracker layouts). Effective area and PSF requirements drive the converter thicknesses and layout. PSF requirements also drive the sensor performance, layer spacings, and drive the design of the mechanical supports. Field of view sets the aspect ratio (height/width) Energy range and energy resolution requirements bound the thickness of calorimeter Electronics Time accuracy provided by electronics and intrinsic resolution of the sensors. On-board transient detection requirements, and on-board background rejection to meet telemetry requirements, are relevant to the electronics, processing, flight software, and trigger design. Instrument life has an impact on detector technology choices. Derived requirements (source location determination and point source sensitivity) are a result of the overall system performance. Astrofisica Gamma

  4. IRD and MSS Constraints Relevant to LAT Science Performance Lateral dimension < 1.8m Restricts the geometric area. Mass < 3000 kg Primarily restricts the total depth of the CAL. Power < 650W Primarily restricts the # of readout channels in the TKR (strip pitch, # layers), and restricts onboard CPU. Telemetry bandwidth < 300 kbps orbit average Sets the required level of onboard background rejection and data volume per event. Center-of-gravity constraint restricts instrument height, but a low aspect ratio is already desirable for science. Launch loads and other environmental constraints. Astrofisica Gamma

  5. X X X Y Y Y Tracker/Converter Issues Expanded view of converter-tracker: Some lessons learned from simulations g At low energy, measurements at first two layers completely dominate due to multiple scattering-- MUST have all these hits, or suffer factor ~ 2 PSF degradation. If eff = 90%, already only keep (.9)4= 66% of potentially good photons. => want >99% efficiency. At 100 MeV, opening angle ~ 20 mrad All detectors have some dead area: if isolated, can trim converter to cover only active area; if distributed, conversions above or near dead region contribute tails to PSF unless detailed and efficient algorithms can ID and remove such events. Low energy PSF completely dominated by multiple scattering effects: q0 ~ 2.9 mrad / E[GeV] (scales as (x0)½) High energy PSF set by hit resolution/plane spacing: qD ~ 1.8 mrad. ~1/E PSF At higher energies, more planes contribute information: Energy# significant planes 100 MeV 2 1 GeV ~5 10 GeV >10 Roll-over and asymptote (q0 and qD)depend on design Astrofisica Gamma E

  6. e– e+ Large Area Telescope (LAT) Overview Tracker • Precision Si-strip Tracker (TKR) • 18 XY tracking planes. Single-sided silicon strip detectors (228 mm pitch), 880,000 channels. • Tungsten foil converters • 1.5 radiation lengths • Measures the photon direction; gamma ID. • Hodoscopic CsI Calorimeter(CAL) • Array of 1536 CsI(Tl) crystals in 8 layers. 3072 spectroscopy chans. • 8.5 radiation lengths • Hodoscopic array supports bkg rejection and shower leakage correction • Measures the photon energy; images the shower. • Segmented Anticoincidence Detector (ACD) • 89 plastic scintillator tiles. • Rejects background of charged cosmic rays; segmentation minimizes self-veto effects at high energy. • Electronics System • Includes flexible, robust hardware trigger and software filters. ACD [surrounds 4x4 array of TKR towers] Calorimeter Astrofisica Gamma

  7. g e+ e- Overview of the Large Area Telescope • Overall modular design: • 4x4 array of identical towers - each one including a Tracker, a Calorimeter and an Electronics Module. • Surrounded by an Anti-Coincidence shield (not shown in the picture). • Tracker/Converter (TKR): • Silicon strip detectors (single sided, each layer is rotated by 90 degrees with respect to the previous one). • W conversion foils. • ~80 m2 of silicon (total). • ~106 electronics chans. • High precision tracking, small dead time. • Anti-Coincidence (ACD): • Segmented (89 tiles). • Self-veto @ high energy limited. • 0.9997 detection efficiency (overall). • Calorimeter (CAL): • 1536 CsI crystals. • 8.5 radiation lengths. • Hodoscopic. • Shower profile reconstruction (leakage correction) Astrofisica Gamma

  8. Benefits of Modularity • Construction and Test more manageable, reduce costs and schedule risk. • Early prototyping and performance tests done on detectors that are full-scale relevant to flight. • Aids pattern recognition. • Good match for triggering large-area detector with relatively localized event signatures. Issue: demonstrate that internal dead areas associated with support material and gaps between towers are not a problem. Resolution: Detailed Monte-Carlo model of instrument, combined with beam-test data of prototype hardware, used to validate design performance. Astrofisica Gamma

  9. Detector Choices TRACKER single-sided silicon strip detectors for hit efficiency, low noise occupancy, resolution, reliability, readout simplicity. Noise occupancy requirement primarily driven by trigger. CALORIMETER hodoscopic array of CsI(Tl) crystals with photodiode readout ANTICOINCIDENCE DETECTOR segmented plastic scintillator tiles with wavelength shifting fiber/phototube readout for high efficiency (0.9997 flows from background rejection requirement) and avoidance of ‘backsplash’ self-veto. for good resolution over large dynamic range; modularity matches TKR; hodoscopic arrangement allows for imaging of showers for leakage corrections and background rejection pattern recognition. Astrofisica Gamma

  10. Tracker Optimization • Radiator thickness profile iterated and selected. • Resulting design: “FRONT”:12 layers of 3% r.l. converter “BACK”: 4 layers of 18% r.l. converter followed by 2 “blank” layers • Large Aeff with good PSF and improved aspect ratio for BACK. • Two sections provide measurements in a complementary manner: FRONT has better PSF, BACK greatly enhances photon statistics. • Radiator thicknesses, SSD dimensions (pitch 228 microns), and instrument footprint finalized. TKR has ~1.5 r.l. of material. Combined with ~8.5 r.l. CAL provides 10 r.l. total. Astrofisica Gamma

  11. Anatomia di una torre 38 C-fiber facesheets • 576 SSD • 55K channels • 228 mm pitch 19 Al honeycomb 38 C-C MCM closeouts 38 C-C structural closeouts 36 Multi-Chip Modules 4 C-fiber sidewalls 8 kapton flex cables 36 kapton bias circuits ~ 1000 screws (several types) 192 3% X0 W tiles 64 12% X0 W tiles glue, paint, tape …… Astrofisica Gamma

  12. SSD Procurement, Testing SLAC,Japan, Italy (HPK) SSD Ladder Assembly Italy (G&A, Mipot) 10,368 342 2592 Tray Assembly and Test Italy (G&A) 342 Electronics Fabrication, burn-in, & Test UCSC, SLAC (Teledyne) 648 Composite Panel, Converters, and Bias Circuits Italy (Plyform): fabrication SLAC: CC, bias circuits, thick W, Al cores Tracker construction workflow Module Structure Components SLAC: Ti parts, thermal straps, fasteners. Italy (Plyform): Sidewalls 18 Tracker Module Assembly and Test Italy (INFN, Alenia Spazio) inter-tower stay-clear 2mm inter-ladder // 100mm Readout Cables UCSC, SLAC (Parlex) Astrofisica Gamma

  13. Silicon strip sensors Standard design Aggressive specs • Hamamatsu Photonics qualified producer • 11500 SSDs delivered (~>90 m2 of active Si) (10368 for 18 towers + spare, wastage, prototype) • up to 700 SSD/month • fully tested at HPK • body IV, CV  final rejection rate ~0.5%

  14. Ladders testing Ladders probe station: 5 probes are used to measure body and single strip I, C to check sanity of each single channel • Flight ladders production: • Total construction 2700 • rejected ~ 1% • 0.016% bad chans caused by bonding or probing • 2mm RMS alignment spread • All results in good agreement with what expected from SSDs Astrofisica Gamma

  15. > 11500 SSD from HPK tested in 3.5 years • 0.5% rejection rate • ~2900 ladders built by industry (G&A, Mipot) and tested in ~ 3 years • ~ 1% ladder rejection rate • 370 bare panels assembled by industry (Plyform) Astrofisica Gamma

  16. Tray assembly Tray positioning Ladder positioning Microbonding Astrofisica Gamma

  17. Tray test • Stack of trays: • functional tests/CR burn-in for a whole tower in parallel • external trigger capability • 4 stacks operating in parallel Astrofisica Gamma

  18. Trays burn-in test with C.R. Trays thermal cycle • 360 trays integrated (Si/MCM/mechanics) by industry (G&A) Tray test by INFN >540 equivalent days of operation for space qual • 3 non-flight trays (bad channels >1% any side) due to delaminations in the MCM • good for calibration unit (max bad chans on one side 9%, average 4%) Astrofisica Gamma

  19. Tower assembly Astrofisica Gamma

  20. Tower assembly and alignment • Many different components are integrated into the tracker: • the excellent intrinsic precision of base components (SSD, 2mm rms wafer cut precision) is fully exploited and maintained in higher level components (e.g. measured ladders displacement (X/Y/Z) on trays has an RMS ~ 20mm) • assembly procedures overcome limitations from specific materials (composites, glue) and deliver integrated units (trays, towers) with monolithic performance • the silicon layer position in the tower can be controlled offline with 3 parameters (Dx/y, DZ, Df)  only 1728 constants for the LAT (>55K for single SSD) CR layer residual after offline corrections MC layer residual perfect geometry rms= 137 mm rms= 124 mm what remains after the correction is very similar to MC data, where only intrinsic tracking fluctuations hold (single hit resolution and multiple scattering) Astrofisica Gamma

  21. Environmental tests in Alenia Accelerometers liquid N2 shroud TV chamber Radiator for power dissipation Astrofisica Gamma Vibrational test

  22. The Silicon Tracker performance • Construction/testing highlights: • Average detection efficiency higher than 99.5% @ the nominal threshold setting. • Single strip noise occupancy lower than 10-6. • Flight production completed in less than one year. 11500 sensors 360 trays 18 towers ~ 1M channels 83 m2 Si surface Astrofisica Gamma

  23. 97.7 % of layers have efficiency >= 99% Silicon layers detection efficiency <= • very similar performance for all >11500 SSD • carefully grouped for ladder and tray assembly based on Vdep Astrofisica Gamma

  24. The GLAST-LAT Calibration Unit • 2.5 towers, >1/8 of the LAT • 110k Si strip • 288 CsI logs + 5 ACD tiles on ISC TKR 8 TKR 16 tower 1 tower 2 tower 3 bay 0 CAL 109 CAL 119 CAL 101 Astrofisica Gamma

  25. The CU in the experimental area and first online events CU VME GASU TRGbox FREE 28V PS ISC ACD XYZq Table 7/25/2006

  26. The H4-SPS Beam Test • Beams • e-, p, p 10-300GeV mostly clean • Focus on • High energy EM shower • High occupancy in TKR • ACD backsplash • Installation completed on sept 5 • Data taken up to sept 16 Astrofisica Gamma

  27. Double gammas in the CU Must correctly simulate them and filter with proper analysis cut From VLE tagged-g Could see these in real-time using Socket-Gleam Astrofisica Gamma

  28. More photons g Astrofisica Gamma

  29. More photons p sneaking dump g Astrofisica Gamma

  30. 280 GeV electrons Astrofisica Gamma

  31. First comparison of g data with MC Full-brem data CAL log E deposit Full-brem data angular distribution Astrofisica Gamma Lott  within few hours from raw data, thanks to MC, recon, pipeline!

  32. 2.5GeV e beam Gamma Tagger for photon data • Tagger operation • Several E beam • Constant E/BL to preserve geometry • Resolution worse at low E • Modified geometry at the end for Low and Very Low E • Carefully planned calibration strategy and online tools to minimize time to few hours • Maximum bending power with low E beam • Crucial for energy recon studies • e energy (tagger) • g energy (CU) • sum Tagged g spectrum combined Astrofisica Gamma Brez, Baldini, Sgro, Bregeon

  33. Integration and test at SLAC 8 TKR towers in the GRID half LAT) 8 towers g candidate events TKR inter-tower alignment (top) 1stg event Astrofisica Gamma

  34. Astrofisica Gamma

  35. Astrofisica Gamma

  36. x x x • CAL: LO – independent check on TKR trigger. HI – indicates high energy event disengage use of ACD. LAT Instrument Triggering and Onboard Data Flow Level 1 Trigger On-board Processing Hardware trigger based on special signals from each tower; initiates readout Function: • “did anything happen?” • keep as simple as possible full instrument information available to processors. Function: reduce data to fit within downlink Hierarchical process: first make the simple selections that require little CPU and data unpacking. • complete event information • signal/bkgd tunable, depending on analysis cuts: :cosmic-rays~ 1:~few • • subset of full background rejection analysis, with loose cuts • only use quantities that • are simple and robust • do not require application of sensor calibration constants • TKR 3 x•y pair planes in a row** workhorse gtrigger OR Total L3T Rate: <25-30 Hz> (average event size: ~8-10 kbits) Upon a L1T, all towers are read out within 20ms On-board science analysis: transient detection (AGN flares, bursts) Instrument Total L1T Rate: <4 kHz> Spacecraft **4 kHz orbit averaged without throttle (1.8 kHz with throttle); peak L1T rate is approximately 13 kHz without throttle and 6 kHz with throttle). Astrofisica Gamma

  37. select quantities that are simple to calculate. Intelligent use of ACD information to preserve acceptance of high-energy events. Filter scheme is tunable. Filters use ACD info: match simple tracks to selected hit ACD tiles, count # hit tiles at low energy CAL info: energy deposition pattern consistent with downward-going electromagnetic interactions. TKR info: remove low-energy particles up the ACD-TKR gap by projecting track to CAL face and selecting on XY position; for very low CAL energy, require TKR hit pattern inconsistent with single prong. filter first designed using LAT simulation/reconstruction, then pieces implemented by FSW group. Now wrapping existing FSW code for use in LAT simulation/recon packages for verification and optimization for science. On-board Filters Astrofisica Gamma

  38. GLAST - Sommario Astrofisica Gamma

  39. Field of View and Instrument Aspect Ratio For energy measurement and background rejection, want events to pass through the calorimeter*. The aspect ratio (Area/Height) then governs the main field of view of the tracker: EGRET had a relatively small aspect ratio GLAST has a large aspect ratio TKR TKR CAL CAL *note: “peripheral vision” events useful at low energy, but are not included in performance calculations. Astrofisica Gamma

  40. LAT Instrument Performance More than 40 times the sensitivity of EGRET Large Effective Area (20 MeV – > 300 GeV) Optimized Point Spread Function (0.35o @ 1 GeV) Wide Field of View (2.4 sr) Good Energy Resolution (DE/E < 10%, E >100 MeV) Astrofisica Gamma

  41. GLAST - EGRET - SKY EGRET, All Years, E> 100 MeV GLAST, 1 Year, E> 100 MeV Astrofisica Gamma

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