GLAST. Gamma Ray Large Area Space Telescope. Hartmut F.-W. Sadrozinski. Science Design Performance. Santa Cruz Institute for Particle Physics (SCIPP)

Transcription

1 GLAST Gamma Ray Large Area Space Telescope Science Design Performance 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 Understand particle acceleration in AGN, Pulsars, & SNRs Resolve the γ-ray sky: unidentified sources & diffuse emission Determine the high-energy behavior of GRBs & Transients Gamma Ray 4 x 4 Array of Towers Anticoincidence Shield 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 Tracker Module Calorimeter Module Grid International and experienced team Broad experience in high-energy astrophysics and particle physics (science + instrumentation) Resources identified, commitments made by partners Management structure in place Broad E/PO program 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 photoelectric Compton pair-conversion 1x10-6 1x10-3 1x10-2 1x10-1 1x10 0 1x10 1 1x10 2 1x10 3 1x10 4 1x10 5 charged particle anticoincidence shield conversion foils Energy (MeV) γ 2 1 particle tracking detectors e+ e- calorimeter (energy measurement)

4 Detector Design Instrument 16 towers modularity height/width = 0.4 large field-of-view TKR Si-strips: fine pitch 201 µm & high efficiency 0.44 X 0 front-end reduce multiple scattering 1.05 X 0 back-end increase sensitivity > 1 GeV CAL CsI: E/E <10 % GeV hodoscopic cosmic-ray rejection shower leakage correction X TOT = 10.1 X 0 shower max contained < 100 GeV ADC segmented plastic scintillator minimize self-veto > efficiency & redundant readout TKR+CAL: prototypes + 1engineering model 16 flight +1(qual spare) +1(spare) ACD: 1(qual) +1 flight

5 GLAST at a Glance

6 Science capabilities - sensitivity 100 s 1 orbit large field-of-view 200 γ bursts per year prompt emission sampled to > 20 µs AGN flares > 2 mn time profile + E/E physics of jets and acceleration γ bursts delayed emission 1 day 3EG limit all 3EG sources + 80 new in 2 days periodicity searches (pulsars & X-ray binaries) pulsar beam & emission vs. luminosity, age, B 1 yr 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)

7 Key Science Objective: Determine the 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

8 Source Catalogs 2 days of the survey: 344 sources GRB, AGN, 3EG + Gal. plane & halo sources Catalog strategy precise interstellar emission model new statistical analyses including variability and spectral signatures > 1 GeV Transients or Flares rapid alert for GRBs ( 15 s to the ground) sky survey data analyzed on a daily basis timely IAU circulars and WWW announcements GRB catalog distinguish unresolved gas clumps flux histories cross references M31 with > 1 GeV astronomical catalogs

9 GLAST Source Localization Capability Expected number of AGN detected with LAT at b > 30 o for 2 year survey sources ~4500 sources 1 year, all-sky survey source localization capability Spectral cutoff above 3 GeV 1 spectral index -2 s/c systematics will limit source localization capability to > 0.3` - - -

10 Key Science Objective: Understand Mechanisms of Particle 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

11 GLAST Key Science Objective: Probe dark matter Dark Matter Candidates (e.g. SUSY particles) would lead to mono-energetic gamma lines through the annihilation process. X X q q or γγ or Zγ GLAST has good sensitivity for a variety of MSSModels in the GeV range, Good energy resolution in the few % range is needed..

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

13 Importance of Energy Reach At low energy, angular resolution is determined by multiple scattering θ rms ~ 1/E, multiple scattering At high energy, resolution is determined by detector resolution σ meas and lever arm d over which measurement is made. Lever arm restricted by fact that direction measurement must be made before 1 st bremsstrahlung photon is emitted. Maximum Likelihood test statistic for detection of point sources. For typical spectral indices, the sensitivity is maximum in the GeV energy domain. θ rms ~ σ meas /d, detector resolution limit Large field of view demands small aspect ratio which means small σ meas hence silicon detectors. Steeply falling spectra require large effective area to reach the detector limit.

14 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]

15 Optimization of Pitch Trade: Performance vs. Resources (Power) GLAST LAT Front 68% Containment vs. Pitch 1 0.1GeV 1GeV 10GeV y = x R= y = x R= y = x R= Pitch [micron] Angular resolution is multiple scattering dominated at low energy (<1GeV). At High Energy, measuring precision is dominant, but lever arm of measurement still limited by accumulated multiple scattering in traversed planes. Changing pitch from 201 to 282 micron, PSF(68) (@ 10GeV ) + 12% Power - 25% Noise (Leakage currents) + 3 % Noise (Capacitance) - 7 % Improved efficiency for large angles

16 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 Vectran cables run through the corner posts to compress the stack. Carbon thermal panel

17 Tracker Module: Tray The tray must be very stiff to avoid collisions (f 0 >500 Hz). A R&D effort is in progress at Hytec Inc. (Los Alamos, NM) to make tray structures entirely from carbon fiber. Hytec is developing the carbon-fiber walls, hex-cell cores, and face sheets. 4 4 array of Si sensors arranged in 4 ladders Kapton bias circuit C-fiber face sheet 9.2cm x 9.2cm detectors Prototypes from HPK Order to STM GLAST Needs: ~10k detectors from 6 wafers ~ 1M readout channels > 5M bonds Hex cell core Al closeout C-fiber face sheet 4 4 array of Pb foils Carbon thermal panel Kapton bias circuit Electronics board 4 4 array of Si sensors arranged in 4 ladders

18 Electrical Interfaces Detector Bias circuit Detector bias: 2-layer Kapton flex circuit Top layer: pads for conductive adhesive, to carry the bias current to the detectors. Bottom layer: hatched ground plane, to isolate the detector bias from the conductive tray structure. Standard space-qualified industrial processes are adequate for this. Tray Structure Backing plate, thermal gasket Plastic extrusion with flex circuit bonded around the curve Readout IC Hybrid PC board, attached by screws >1600 fine traces bend around the corner. Old bias circuit layout (1st prototype) New concepts: The bias circuit HV and ground plane are divided into 4 separate circuits. We need to reevaluate the gluing pattern. The flex circuit for wrapping around the corner is separate from the bias circuit and is part of the hybrid assembly. It has 1 trace for each detector strip, plus bias and ground connections for each ladder.

19 1997 Beam Test of Prototypes Results of 1997 beam test of instrument components: Atwood, W.B. et al. 1999, NIM A (in press) Layout of beam test tracker. For configuration on left, the converter/detector planes are 3 cm apart; Layout of hodoscopic CsI beam test calorimeter on the right the separation is 6 cm.

20 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

21 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)

22 Hiroshima 2000 : GLAST Challenge # 3: 1M channels, 250W Power See Takanobu Handa s Poster Redundant, ultra-low power, low-noise FEE 28 Amplifier chips Hybrid: Electrical & mechanical Challenge Boss for mechanical and thermal attachment to the wall. Digital readout controller chip at each end Kapton Cable down the Tower Walls 25-pin Nanonics connector Cross-over into the side arms Lengthy run past the Calorimeter, needs shielding around cable. TEM 4 layers of 1/2 oz copper traces and power/ground planes Power filtering, and connection of digital and analog grounds to the shield here. Termination Resistors Digital 3.3V Digital Ground LVDS Signals Bias + Analog 3.3V Analog Ground Analog 1.5V Digital Analog

23 Occupancy Hiroshima 2000 : 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 occupancy was obtained by inducing triggers, followed by readout, at random times. 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

24 Hiroshima 2000 : GLAST Tracker of the Beam Test Engineering Module The BTEM Tracker, with 16 x,y planes, underwent tests in the SLAC test beam (11/99 1/00). - partially (81%) instrumented with detectors - all detectors are in 32 cm long ladders. BTEM Tracker Module with side panels removed. Single BTEM Tray End of one readout hybrid. See Eduardo de Couto e Silva s talk

25 GLAST Team E/PO Principal Investigator P. Michelson (Stanford University) Project Manager W. Althouse (SU-SLAC) Collaboration Science Team Senior Scientist Advisory Committee Tracker UCSC, SU- SLAC, Japan, Italy Calorimeter NRL, France, Sweden DAQ SU, NRL ACD GSFC Grid Thermal SU-SLAC Inst. Ops. Ctr. SU-HEPL Country co-investigators associates Science Team: experienced in Astro and HEP USA France 6 3 Japan 4 5 Italy 3 2 Sweden 2 2 Germany 3

26 GLAST Development Process and Status Date Activity Program Result Conceptual study NASA SR&D Beam Test 1998: Detector R&D DoE R&D Verification of Simulations 98 DoE Review SAGENAP Endorsement Technology Development NASA ATD BTEM Full Size Modules Manufacturing Process ASIC s, DAQ Fall 99 GLAST Instrument Proposal NASA AO GLAST Base Line Instr. (Si Tracker, CsI Calorimeter, ACD) Budget, Schedule, WBS Endorsements, MoA Feb 25, 00 Decision on AO Si-GLAST selected Sept 2005 Launch on Delta 2

27 GLAST Schedule Calendar Years SRR I-PDR NAR M-PDR I-CDR M-CDR Inst. Delivery Launch Formulation Implementation Ops. Build & Test Engineering Models Build & Test Flight Units Inst. I&T Inst.-S/C I&T Procurement of ~10k Si Detectors Schedule Reserve