Radiation Issues in GLAST Si

Transcription

1 Radiation Issues in GLAST Si Science Design of Challenges Radiation Issues Hartmut F.-W. Sadrozinski Santa Cruz Institute for Particle Physics (SCIPP)

2 GLAST Gamma-Ray Large Area Space Telescope An Astro-Particle Physics Partnership Exploring the High-Energy Universe Design Optimized for Key Science Objectives 4 x 4 Array of Towers Anticoincidence Shield Understand particle acceleration in AGN, Pulsars, & SNRs Resolve the γ-ray sky: unidentified sources & diffuse emission Determine the high-energy behavior of GRBs & Transients Proven technologies and 7 years of design, development and demonstration efforts Precision Si-strip Tracker (TKR) Hodoscopic CsI Calorimeter (CAL) Segmented Anticoincidence Detector (ACD) Advantages of modular design NASA, DoE, DoD, INFN/ASI, Japan, CEA, IN2P3, Sweden Gamma Ray Tracker Module Calorimeter Module Grid Challenges of Science in Space Launch Limited Resources Space Environment Resolving the γ-ray sky

3 GLAST Detector Concept: Pair Conversion Telescope 1x10 1 Photon attenuation in lead photon attenuation length (cm) 1x10 0 1x10-1 1x10-2 1x10-3 1x10-4 1x10-5 1x10-6 charged particle anticoincidence shield conversion foils photoelectric Compton pair-conversion 1x10-3 1x10-2 1x10-1 1x10 0 1x10 1 1x10 2 1x10 3 1x10 4 1x10 5 Energy (MeV) γ 2 1 particle tracking detectors e+ e- calorimeter (energy measurement)

4 Science capabilities - sensitivity 100 s 1orbit large field-of-view 200 γ bursts per year prompt emission sampled to > 20 µs AGNflares> 2mn time profile + E/E physics of jets and acceleration γ bursts delayed emission 1day 3EG limit all 3EG sources + 80 new in 2 days periodicity searches (pulsars & X-ray binaries) pulsar beam & emission vs. luminosity, age, B 1yr LAT 1 yr cm -2 s sources in 1-yr survey AGN: logn-logs, duty cycle, emission vs. type, redshift, aspect angle extragalactic background light (γ + IR-opt) new γ sources (µqso, external galaxies, clusters)

5 Science: High-Energy Behavior of GRBs Important GLAST properties for achieving science objectives: Large area Low instrument deadtime (20 µs) Energy range to >300 GeV Large FOV Expected Numbers of GRBs and Delayed Emission in GLAST GLAST will probe the time structure of GRB s to the µs time scale Spectral and temporal information might allow observation of quantum gravity effects. Time between detection of photons

6 Science: Acceleration in AGN, Pulsars, & SNRs Multi-wavelength Observations are crucial for the understanding of Pulsars and AGN s. Flares are largest at high energy. Overlap of GLAST with ACT s provides Needed energy calibration. Mk 501 Flares Crab Synchrotron Radiation Inverse Compton

7 Instrument Performance (Single Source F.o.M ~ Aeff /[σ(68%)] 2 ) FOV: 2.4 sr SRD: 2.0 sr

8 Optimization of Converter Thickness t Effective Area vs. Conversion Plane Graded Converter (2.5%, 25%) Uniform Converter (3.5%) A eff ~ t For Background limited Sources: (Significance) = A eff / PSF(68) 2 is independent of Converter Thickness x-y Plane For High Latitude Sources: Number of detected gamma s count. 10 Gamma Angular Resolution PSF(68) 68% Front 68% Back # of Layers X 0 per Layer γ Conversion [ o ] 1 Front % 38% PSF(68) ~ t Back 4 26% 38% Gamma Energy [GeV]

9 Overview of TKR Baseline Design 16 towers, each with 37 cm 37 cm of Si (78m 2 in all) One Tracker Tower Module 18 x,y planes per tower 19 tray structures 12 with 2.5% Pb on bottom 4 with 25% Pb on bottom 2 with no converter Every other tray rotated by 90, so each Pb foil is followed immediately by an x,y plane 2mm gap between x and y Electronics on the sides of trays Minimize gap between towers 9 readout modules on each of 4 sides Trays stack and align at their corners The bottom tray has a flange to mount on the grid Carbon-fiber walls provide stiffness and the thermal pathway to the grid Electronics flex cables Carbon thermal panel

10 Silicon-Strip Detectors 400 µm thick, single sided 8.95 cm 8.95 cm (6 wafers) Strip pitch: 228 µm AC coupled with polysilicon bias (~60MΩ) Qualify Prototypes from HPK Guard Ring Bias Ring Bias Resistors DC Pads 80 x 80 AC Pads 80 x 150 Pitch 194 GLAST Needs: ~10k detectors from 6 wafers ~ 1M readout channels > 5M bonds Pads for Bypass Al Traces 80x150 Schematic layout of the detector. Bypass strips will not be used. DC pads will increase in size. A second AC pad will be added on each strip, for probing and for a second chance at wire bonding. Bypass strip

11 Tracker of the Beam Test Engineering Module The BTEM Tracker, (~1/16 of the flight instrument) for the SLAC test beam (11/99 1/00) - 2.7m 2 silicon, ~500 detectors, 42k channels - all detectors are in 32 cm long ladders. BTEM Tracker Module with side panels removed. Single BTEM Tray End of one readout hybrid. Si Detectors HPK 296 (4 ), 251 (6 ) Micron 5 (6 ) Leakage I: 300 na/detector (HPK) Bad strips: about 1 in 5000

12 Assembly of BTEM Tracker at SCIPP 2 trays and 2 observers 4 trays, 10 eyes & 10 hands 2 delicate hands All done and all smiles. 17 trays!

13 Challenge #1 : Space Environment and Launch Aluminum and carbonfiber mechanical model of 10 stacked tracker trays, used by Hytec, Inc. to validate the design in vibration tests. FEM analysis of (a) TKR tray deflections and (b) of a complete TKR module. Fundamental frequencies are above 550 Hz for the tray and 300 Hz for the module, clamped only at its base. Space Qualification: Assembly Methods Materials Tests BTEM TKR tray undergoing random vibration testing at GSFC. Vibration Testing of a live tray up to 14g. Leakage current before and after shaking identical

14 Challenge #2: On Board Cosmic Ray Rejection C.R. Rejection needed 10 5 : 1 segmented ACD segmented CAL segmented TRK LVL1 : 5kHz Downlink: 30Hz Diffuse High Latitude gamma-ray flux Radiation Levels: 1krad in a 5year mission Issue: SEE from Heavy Ions (SEU & Latch-up) See below

15 Challenge # 3: 1M channels, 250W Power Redundant, ultra-low power, low-noise FEE See Takanobu Handa s Poster TEM Hybrid: Electrical & mechanical Challenge Boss for mechanical and thermal attachment to the wall. 28 Amplifier chips Kapton Cable down the Tower needs shielding around cable. Walls 25-pin Nanonics connector Digital 3.3V Digital Ground LVDS Signals Term 4 layers of 1/2 oz copp Resis Cross-over into the side arms Digital Digital readout controller chip at each end Analog Bias + Analog 3.3V Analog Ground Analog 1.5V

16 Occupancy F2k : GLAST Challenge #4: Tracker Noise and Efficiency 1.1 Noise occupancy determines the noise rate of the LVL1 trigger, a coincidence of 6 OR d layers. Noise RMS σ = *C/pF [e - ], τ =1.3µs Hit efficiency was measured using single electron tracks and cosmic muons. The requirements were met: 99% efficiency with <<10 4 noise occupancy Layer 6x 100,000 triggers Strip Number Noise occupancy and hit efficiency for Layer 6x, using in both cases a threshold of 170 mv. No channels were masked. Efficiency Hit Efficiency Layer 10 x Layer 10 y Threshold (mv) Hit efficiency versus threshold for 5 GeV positrons. Cosmic Rays Electron Beam Layer 6x Detector Ladder

17 Space Environment: Radiation GLAST is in a Low-Earth Orbit (550km): Shielding of Atmosphere and magnetic Field Avoid (most!) of the radiation belts Orbit co-determined by Re-entry > 10 Years, < 30years. USA on ARGOS Radiation Belts: - High Latitude South Atlantic Anomaly (SAA)- Trapped electrons and protons responsible for Total Dose cause huge trigger rate (Detectors will be switched off) Outside radiation Belts: Charged Cosmic Ray Background (p, e, heavy ions) Responsible for Single Event Effects (SEE)

18 Radiation: Total Dose & Displacement Long-term Radiation Damage: Entirely given by electron and proton flux trapped in the SAA Extremely soft spectrum: Self shielding of Instrument: Blanket, ACD, walls: 2.50g/cm 2 Cut-off at 80MeV protons GLAST Silicon Tracker End-of-Mission Signal-to-Noise Electrons Bremsstrahlung Protons Total Depth (g/cm 2 Al) Full dose - Spherical shield 550 km 28 circular orbit 5-year mission - Solar Minimum Total Dose 1kRad (5 yrs) -NASA safety factor: 5x- Leakage current increase 50% surface, 50% bulk (same temperature dependence) S/N E-o-M 1x S/N E-o-M 5x Increase in shot noise due to radiation constrains operating temperature to below 25 o C. Temperature [deg C]

19 Heavy Ion Radiation: Temporal Effects (SEE) Linear Energy Transfer LET governs Single Event Effects: SEU, SEL, Punch Through LET is de/dx: LET (Min ion) 1.3*10-3 MeV/(mg/cm 2 ), LET ~ Z 2 : LET (Fe) 1-2 MeV/(mg/cm 2 ). Update from AMS Fe GLAST IRD

20 Heavy Ion Radiation: Single Event Upset Credit:

21 Silicon Detectors in High Radiation Fields Past Problems beam loss LEP (CERN) Future (?) Problems High Luminosity colliders (BaBar, ATLAS) Detectors in Space(?) (GLAST) ALEPH/Babar detector shorted out due to beam loss; unexpected large voltage across coupling capacitance prepare for large ionization in Silicon microstrip detectors either from beam loss or minimum bias particles heavy ions (Fe) will have ionization power of 1000 s of minimum ionizing particles Beam loss is measured in fluence [MIPs / cm 2 ] or total absorbed dose(si) [Rad] In 300µm thickness 1 Rad = 10 6 MIPs/ cm 2 Detectors are designed for MIP signal: 1MIP = 4fC = 24,000 electron-holes pairs Detectors might not be optimized for high radiation field

22 GLAST Challenges from Radiation Total Dose and Displacement requirements are modest, but shot noise increase is noticeable due to detector length and long shaping time. Limit on operating temperature. SEE is more demanding and need careful testing. Tests with lasers and heavy ion beams needed to make sure that SEE is not a problem. Choice of CMOS technology helps: either SoI or HP 0.5um are attractive. SEU hardened design and SEL resistant design are fallback. SEU: Frequent refreshing of registers advisable. Detectors are susceptible to breakdown for large LET. Specify coupling capacitors for full operating voltage.

23 GLAST Development Process and Status Date Activity Program Conceptual study NASA SR&D Detector R&D DoE R&D (Beam Test 1998) 98 DoE Review SAGENAP Endorsement Technology NASA ATD Development (BTEM Full Size Modules Manufact. Process ASIC s, DAQ) What New Worlds are we going to see? Fall 99 Instrument Proposal NASA AO GLAST Base LIne (Si TKR, CsI CAL, ACD) Endorsements, MoA Feb 25, 00 Decision on AO GLAST-LAT selected Sept 2005 Launch on Delta 2