GLAST an AstroParticle Mission to Explore

1
GLAST - an Astro-Particle Mission to Explore the
High Energy Gamma Ray Sky Alessandro Brez INFN
- sez. Pisa
VERTEX 2003 Low Wood Lake Windermere, Cumbria,
UK, September 14-19 2003
2

• SUMMARY
• The GLAST mission, the detector and the science
  goals
• The tracker of GLAST
• Status of the tracker construction and
  Engineering Model results

3
Profound Connection between Astrophysics HEP
The fundamental theory of Cosmic Genesis and the
quest for experimental evidence has led to new
and potential partnerships between Astrophysics
and HEP.

• Some Areas of Collaboration
• Origin of cosmic rays
• Dark Matter Searches
• CMBR
• Quantum gravity
• Structure Formation
• Early Universe Physics
• Understanding the HE Universe

• Typical signatures
• Ultra HE cosmic rays
• gamma-rays -gt GLAST
• n
• antimatter

• extensive use of high resolution and reliable
  particle detectors now possible after long and
  successful experience in particle physics

4
GLAST g detection technique pair conversion
telescope
Pair production is the dominant photon
interaction above 10MeV E? -gt mec2 me-c2

• GLAST Concept
• Low profile for wide f.o.v.
• Segmented anti-shield to minimize self-veto at
  high E.
• Finely segment calorimeter for enhanced
  background rejection and shower leakage
  correction.
• High-efficiency, precise track detectors located
  close to the conversions foils to minimize
  multiple-scattering errors.
• Modular, redundant design.
• No consumables.
• Low power consumption (580 W)

5
GLAST Instrument the Large Area Telescope (LAT)

• Array of 16 identical Tower Modules, each with
  a tracker (Si strips) and a calorimeter (CsI with
  PIN diode readout) and DAQ module.
• Surrounded by finely segmented ACD (plastic
  scintillator with PMT readout).
• Aluminum strong-back Grid, with heat pipes for
  transport of heat to the instrument sides.

6
LAT Instrument Performance
Including all Background Track Quality Cuts
7
The GLAST Participating Institutions
American Team Institutions SU - Stanford
University, Physics Department and EGRET group,
Hanson Experimental Physics Laboratory
SU-SLACStanford Linear Accelerator Center, SLAC,
Particle Astrophysics group GSFC-NASA Goddard
Space Flight Center, Laboratory for High Energy
Astrophysics NRL - U. S. Naval Research
Laboratory, E. O. Hulburt Center for Space
Research, X-ray and gamma-ray branches UCSC-
University of California at Santa Cruz, Physics
Department SSU- Sonoma State University,
Department of Physics Astronomy UW-
University of Washington , TAMUK- Texas AM
University-Kingsville Italian Team Institutions
INFN - Instituto
Nazionale di Fisica Nucleare Units of Bari,
Perugia, Pisa, Rome 2, Tries
ASI - Italian Space Agency
IFC/CNR- Istituto di Fisica, Cosmica,
CNR Japanese Team Institutions University of
Tokyo ICRR - Institute for Cosmic-Ray
Research ISAS- Institute for Space and
Astronautical Science Hiroshima
University French Team Institutions CEA/DAPNIA
Commissariat à l'Energie Atomique, Département
d'Astrophysique, de physique des Particules,
de physique Nucliaire et de l'Instrumentation
Associée, CEA, Saclay IN2P3 Institut
National de Physique Nucléaire et de Physique des
Particules, IN2P3 IN2P3/LPNHE-X Laboratoire
de Physique Nucléaire des Hautes Energies de
l'École Polytechnique IN2P3/PCC Laboratoire
de Physique Corpusculaire et Cosmologie, Collège
de France IN2P3/CENBG Centre d'études
nucléaires de Bordeaux Gradignan Swedish Team
Institutions KTHRoyal Institute of Technology
Stockholms Universitet
8
GLAST science - the sky above 100 MeV
9
Covering the Gamma-Ray Spectrum

• Broad spectral coverage is crucial for studying
  and understanding most astrophysical sources.
• GLAST and ground-based experiments cover
  complimentary energy ranges.
• The improved sensitivity of GLAST is necessary
  for matching the sensitivity of the next
  generation of ground-based detectors.
• GLAST goes a long ways toward filling in the
  energy gap between space-based and ground-based
  detectorsthere will be overlap for the brighter
  sources.

Predicted sensitivities to a point source.
EGRET, GLAST, and Milagro 1-yr survey.
Cherenkov telescopes 50 hours on source.
(Weekes et al., 1996, with GLAST added)
10
Identifying Sources
GLAST 95 C.L. radius on a 5? source, compared
with a similar EGRET observation of 3EG 1911-2000
Unidentified Sources
Counting stats not included.
170/271 3rd EGRET catalog still unidentified
GLAST high resolution and sensitivity will

• resolve gamma-ray point sources at arc-minute
  level
• detect typical signatures (e.g. spectra, flares,
  pulsation) for identification with known source
  types

Cygnus region (150 x 150), Eg gt 1 GeV
11
Halo WIMP annihilations
Good particle physics candidate for galactic halo
dark matter is the LSP in R-parity conserving SUSY
If true, there may well be observable halo
annihilations
If SUSY uncovered at accelerators, GLAST may be
able to determine its cosmological significance
quickly.
12
Supersymmetric Cold Dark Matter searches with
GLAST
Total photon spectrum from galactic centre with
cc annihilation contribution
infinite energy resolution
finite energy resolution
2-year scanning mode
Bergstrom et al.
13
Gamma-Ray Bursts

• GLAST LAT will be best suited to studying the GeV
  tail of the gamma-ray burst spectrum. A separate
  instrument (GBM) on the spacecraft will cover the
  energy range 10 KeV 25 MeV and will provide a
  hard X-ray trigger for GRB.
• GLAST should detect ?200 GRB per year with Egt100
  MeV, with a third of them localized to better
  than 10?, in real time.
• Excellent wide field monitor for GRB. Nearly
  real-time trigger for other wavelength bands,
  often with sufficient localization for optical
  follow-up.
• With a ?10?s dead time, GLAST will see nearly all
  of the high-E photons.

GBM
LAT
Energy dependent lags and the physics behind GRB
temporal properties will be better studied by the
broad energy coverage (10 KeV 100 GeV) provided
by GBM and LAT.
14
Gamma-Ray Bursts

• transient signal, 100 µs time scale
• light curves vs energy
• fast response/ short dead time

• spectral studies for
• non-thermal emission model
• (synchrotron, ICS)
• fireball baryon fraction
• high energy resolution

Simulated time profile of a GRB detected by the
LAT and the GBM. The pulses are narrower at LAT
energies.

• The origin of ultra-energy cosmic rays suggested
  to be GRBs (Waxman 1995)
• Burst of high energy g as signature of the
  evaporation of primordial black holes.

15
GLAST Tracker Design Overview

• 16 tower modules, each with 37cm ? 37cm of
  active cross section
• 83m2 of Si in all, like ATLAS
• 11500 SSD, 1M channels
• 18 x,y planes per tower
• 19 tray structures
• 12 with 3 W on bottom (Front)
• 4 with 18 W on bottom (Back)
• 3 with no converter foils
• Every other tray is rotated by 90, so each W
  foil is followed immediately by an x,y plane of
  detectors
• 2mm gap between x and y oriented detectors
• Trays stack and align at their corners
• The bottom tray has a flange to mount on the
  grid.
• Electronics on sides of trays
• Minimize gap between towers
• 9 readout modules on each of 4 sides

16
Tracker Production Overview
Module Structure Components SLAC Ti parts,
thermal straps, fasteners. Italy (Plyform)
Sidewalls
SSD Procurement, Testing SLAC,Japan, Italy (HPK)
SSD Ladder Assembly Italy (GA, Mipot)
10,368
Tracker Module Assembly and Test Italy (Alenia
Spazio)
2592
18
Tray Assembly and Test Italy (GA)
342
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
Readout Cables UCSC, SLAC (Parlex)
17
SSD Electrical Test Rate
SSD in Italy 9452 (82 of total, enough for 16
towers) SSD tested 7373 (64 of total) SSD to
review 201 SSD rejected 44
Cumulative test rate

18
SSD Electrical Properties
Specification leakage current lt500 nA at 25?C
and 150 V
19
Ladder Assembly
Encapsulated bondings
Ladder assembly tool
Manual fast AND precise method 24 ladder assembly
tools used in parallel Very good ladder alignment
obtained
20
Ladders Electrical Tests

• Electrical test results
• Ladder tested 513
• Accepted 501(98)
• Broken edge 6
• High current 6
• (gt2mA_at_150V)
• The cause of problem 3 has been corrected.

21
Ladders Electrical Tests
Leakage current at 150 V
Depletion voltage
22
Tray Panel Fabrication

• Machining of the Carbon-Carbon closeout material
  is just starting.
• Face sheets, cores, inserts, and tungsten are in
  hand.
• Bias circuits are out for quote.
• PRR actions are being closed.

Gr/CE Face Sheet
C-C Structural Closeout Wall
Thermal Boss
1 lb/ft3 Aluminum Honeycomb Core
C-C MCM Closeout Wall
23
Tracker Tray with Payload

• The tray payload is bonded to the sandwich
  structure using epoxy, with the exception of the
  SSD bonding, which is done with silicone.
• Silicone decouples the thermal/mechanical effects
  from the tray

24
E.M. Results DIMENSIONS
25
Vibrational test
Sine sweep before/after random
Random vibration White noise
Z accelerometer response X accelerometer
response Y accelerometer response
TG07
TG07
Resonance search ?0 815 Hz, Q ? 51
Resonance check ?0 809 Hz, Q ? 49
All the EM trays have been successfully tested at
qualification level. No damages or relevant
frequency shifts have been observed
26
Bare Panel N.D.I. Test
ESPI Thermal Loads very effective to detect bare
panel defects
Skin-closeout debonding
Honeycomb crash
Honeycomb Skin debonding
27
ESPI Vibration TEST
TG07 Bare Panel W Bias Plane
817Hz first resonance mode
1860Hz second resonance mode
28
Assembly phases
Ladder assembly on the trays
29
Ladder alignment results
measurement points
s28mm
MCM side
0.2mm
y
x
s46mm
s32mm
30
Tray box
The tray box allows safe shipping and storage.
Through the connector savers the tray can be
fully tested in the closed box.
Fixation points
Handle
Connector saver
N2 inlet
31
Trays Thermal qualification cycles

• Qualification-like test
• temperature range -30C ? 50C
• T0 24C
• number of cycles 4
• 2 hr _at_ -30 C, 50 C
• (dT/dt) 0.5 C/min

?T25 C ?L/L ? 100 ?? ?T-55 C ?L/L ? - 350
??
Thermal test lot 4 trays/cycle in 4 climatic
chambers (2 ready by Pg in Terni,
1 foreseen in Pi, 1 foreseen in Ba) Test
rate/climatic chamber 1 tower/month
32
Assembly of EM Tower in GA
Trays alignment on assembly jig
Cabling
Geometrical tolerances well within limits (0.3
mm).
33
Mini-Tower Assembly Test
Mini-tower concept 3 XY working planes for
detection capability test
(Aluminum grid fixture is removed)
34
Cosmic Rays Online DATA
The trigger occurs when particles traverse the 6
consecutive layers of the MiniTower.
35
Detection efficiency
Full efficiency plateau up to ? ½ MIP
60
1MIP
36
Spatial resolution
Alignment
37
Integration of MiniTKR and CAL at SLAC
Courtesy of IT team
38
conclusions
GLAST construction is going on with very good
results. The close combined effort of HEP
Institutes with high tech companies lead to a
fast, precise, high yield production. The HEP
Institutes have defined the project and will
conduct the test activity. The industrial
counterpart is essential in defining the more
technological details, provides the specialized
manpower, assure the Quality certification of the
production.