LAT Calorimeter Subsystem

1
LAT Calorimeter Subsystem

• W. Neil Johnson
• Calorimeter Subsystem Manager
• Paolo Carosso
• Calorimeter Project Manager
• Space Science Division
• Naval Research Laboratory
• johnson_at_gamma.nrl.navy.mil

2
LAT Calorimeter Subsystem

• Outline
• Participating Institutions
• Technical Description and Requirements
• Status
• Organization and WBS responsibilities
• Schedule
• Milestones
• Cost Summary
• Key Issues and Concerns

3
Calorimeter Hardware Team

• Naval Research Laboratory (NRL), Washington DC
• Overall scientific and management lead
• System engineering performance assurance
• Electronics
• Software
• Integration, test, and calibration
• Stanford Linear Accelerator Center (SLAC),
  Stanford, CA
• ASIC design and development
• Electronics oversight
• Commissariat à l'Energie Atomique / Direction des
  Sciences de la Matière, Département
  d'Astrophysique, de Physique des Particules, de
  Physique Nucléaire et de l'Instrumentation
  Associée (CEA/DSM/DAPNIA), Saclay, France
• Management, France
• PIN Photodiodes
• LAT Power Supplies
• Centre National de la Recherche Scientifique /
  Institut National de Physique Nucléaire et de
  Physique des Particules (IN2P3) 3 Laboratories
• LPNHE, Ecole Polytechnique - Lead, mechanical
  structure optical performance, assembly and
  test
• PCC, Collège de France - CsI detector elements,
  Simulations, Software
• CENBG of Université de Bordeaux - ASIC Test
  Bench, Beam Test support and analyses
• Royal Institute of Technology (KTH) and Stockholm
  University in Stockholm, Sweden
• CsI Crystals and acceptance testing

4
Large Area Telescope (LAT) Design Overview
Instrument
16 towers ? modularity height/width 0.4 ?
large field-of-view Si-strip detectors 228 mm
pitch, total of 8.8 x 105 ch.
hodoscopic CsI crystal array ?
cosmic-ray rejection ? shower leakage
correction XTkr Cal 10 X0 ? shower max
contained lt 100
GeV segmented plastic scintillator ?
minimize self-veto gt 0.9997 efficiency
redundant readout
Tracker
Calorimeter
Anticoincidence Detector Shield
3000 kg, 650 W (allocation) 1.75 m ? 1.75 m ?
1.0 m 20 MeV 300 GeV
5
Calorimeter Module Concept
Modular Design 4 x 4 array of calorimeter modules

• Mechanical packaging Carbon Composite cell
  structure
• Electronics boards attached to each side.
• Electronic readout to connectors at base of
  calorimeter.
• Outer wall is EMI shield and provides structural
  stiffness as well.

• Each Module
• 8 layers of 12 CsI(Tl) Crystals
• Crystal dimensions 27 x 20 x 336 mm
• Hodoscopic stacking - alternating orthogonal
  layers
• Dual PIN photodiode on each end of crystals.

6
Calorimeter Technical Challenges

• Imaging calorimetry to support background
  rejection and improve energy measurement via
  shower profile correction or leakage estimation.
• Hodoscopic arrangement of CsI crystals, 8 layers
  of 12 crystals
• Longitudinal positioning in individual crystals
  using light asymmetry measurements at each end of
  crystal
• Large dynamic range ( 5 x 105) with low power
  electronics
• Divide signal into two ranges using dual PIN
  Photodiode of differing areas
• Custom CMOS ASIC front end electronics
• Minimize passive material and gaps in active
  material caused by modular design, yet survive 7g
  launch loads.
• Carbon composite structure with individual cells
  for each CsI crystal.
• PIN diode readout via PCB on four sides of
  module.
• EMI/structural outer wall.
• Low dead time (lt 20 usec), low power spectral
  measurements over full energy range.
• Dedicated ADC for each CsI crystal end
• COTS low-power successive approximation ADCs
• In-flight calibration
• Use cosmic rays (p Fe)

7
Beam-Test Prototype Calorimeter Assembly
8
Derived Calorimeter Requirements
9
Calorimeter Design Status

• Full scale prototype designed and fabricated as
  part of NASA Advanced Technology Development
  (ATD) Program
• Tested in SLAC Beam Test, Dec 1999 Jan 2000
• Tested in GSI Beam Test (C, Ni beams), July 2000
• Refurbished for Suborbital flight, planned June
  2001
• Current design builds on ATD prototype with
  significant changes
• Mechanical design is based on carbon composite
  cell structure proposed by IN2P3, based on CMS
  concepts and experience
• Electronics designs and interfaces have been
  modified to reflect the LAT-wide trigger and data
  flow concepts and communications protocols
• Design and fabrication responsibilities were
  redistributed to include major contributions from
  collaborators in France and Sweden
• As a result
• The optical and mechanical performance
  characteristics of the new mechanical packaging
  concept are in progress
• The analog front end ASIC design was delayed for
  two years. The work has recently been
  transferred from France to SLAC.
• Restructuring of the responsibilities and the
  French management requires a re-definition of the
  baseline schedule and costs.

10
Design Status (cont)

• Mechanical Structure
• Prototype fabricated and populated with dummy
  crystals for vibration testing. Vibration
  testing complete.
• Optical properties of structure coating and
  possible crystal wrappings have been studied.
• Crystal Detector Elements
• CsI Crystal procurement has been advertised, 3
  bids have been received for 1st crystals
  delivered by May 01.
• PIN Photodiode specification is complete for
  engineering model prototype diodes.
• Light yield studies completed for various
  wrapping materials.
• PIN diode bonding tests epoxies and silicone
  elastomers have been tested.
• Baseline design uses silicone elastomer bond
  stabilized by external frame that is epoxied to
  CsI crystal tests beginning.
• Electronics
• Test structures for analog front end ASIC are
  under test.
• 1st submission of fully functional ASIC scheduled
  for March.
• Radiation testing (SEU, SEL) of COTS ADCs has
  identified two potential ADCs.

11
Calorimeter Institutional Organization
12
Calorimeter WBS Organization
13
Calorimeter Module Assembly

• 18 Identical Calorimeter Modules
• 2 Calibration Units (Flt spares)
• 16 Flight Units

14
Calorimeter Key Documentation Status
15
4.1.5 Calorimeter
16
Schedule Milestones

• Calorimeter (CAL) Requirements Review 03/14/01
• Interim Subsystem Review 02/28/01
• Interim Subsystem Review 06/29/01
• Calorimeter PDR 07/11/01
• LAT Instrument PDR 08/06/01
• Engineering Model (EM) assembly complete 04/01/02
• Calorimeter CDR 06/05/02
• EM Test complete 06/28/02
• LAT Instrument CDR 08/05/02
• Qual Modules A B Ready for Integration
  (calibration unit) 05/15/03
• Flight Modules 1 2 Ready forIntegration
  (calibration unit) 08/01/03
• Flight Modules 3 16 Ready forIntegration
  
  10/01/03 12/24/03

17
Interim Calorimeter Cost Estimate
(Escalated K)
DOE/NASA funding.
18
Issues

• Delays in committing to and implementing MoA and
  International Agreement are impacting schedule
• NASA now moving forward with International
  Agreement (CNES) MoA is ready for signature
  CAL Implementation Plan being developed
• Hardware responsibilities have been
  re-allocated and French management and
  staffing is underway
• Frequency of technical exchange to increase
  series of face-to-face meetings scheduled and
  committed to focus on finalizing Implementation
  Plan
• Establishing baseline performance by PDR
• Accelerated fabrication and testing of prototype
  PEM structure
• Accelerated PIN diode specification and prototype
  procurement
• Optical bond of PIN diode to CsI crystals
• Issue is degradation of optical quality of bond
  through temperature cycling
• Hard epoxies have failed LAT prototype and
  ESAs Integral Pixit instrument
• Aggressively investigating silicone elastomeric
  pads and soft epoxy solutions
• Qualification of COTS ADC
• Speed and power requirements essentially require
  COTS (commercial off the shelf) successive
  approximation CMOS ADCs.
• Testing 5 different COTS parts from Burr Brown
  and Maxim. SEL measurements on two Maxim parts
  are encouraging
• SEU testing at Brookhaven will occur in March.
• Fabrication, test, calibration and delivery
  schedule for 16 flight modules.
• Delivery rate represents schedule risk will work
  closely with LAT IPO to optimize overall schedule