ACD Subsystem

GLAST LAT Project DOE/NASA Review of the GLAST/LAT Project, Feb. 13-15, 2001

J. Ormes/R. Larson 1

ACD SubsystemACD Subsystem

Jonathan F. OrmesACD Subsystem Manager

Rudolph K. LarsenACD Project Manager

Laboratory for High Energy AstrophysicsNASA Goddard Space Flight Center

[email protected]



Anti-Coincidence (ACD) SubsystemAnti-Coincidence (ACD) Subsystem

Technical overview Requirements Status Organization Schedule Budget Technical issues and mitigations Summary

Outline



Large Area Telescope (LAT) Design OverviewLarge Area Telescope (LAT) Design Overview

16 towers modularityheight/width = 0.4 large field-of-view

Si-strip detectors: 228 m 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 < 100 GeV

segmented plastic scintillator minimize self-veto > 0.9997 efficiency & redundant readout

InstrumenInstrumentt

TrackerTracker

CalorimeteCalorimeterr

Anticoincidence Detector Anticoincidence Detector ShieldShield 3000 kg, 650 W

(allocation)

1.75 m 1.75 m 1.0 m

20 MeV – 300 GeV



ACD: The First Line of Defense Against BackgroundACD: The First Line of Defense Against Background

• The purpose of the ACD is to detect incident cosmic ray charged particles that outnumber cosmic gamma rays by more than 5 orders of magnitude. Signals from the ACD can be used as a trigger veto or can be used later in the data analysis.

• Segmented plastic scintillator (Bicron-408) read with wave-shifting fibers (BCF- 91MC) + PMT (Hamamatsu R1635, R4868) readout.• Each segment (tile) has a separate light tight housing. • Separate tile housings provide resistance to accidental puncture by

micrometeoroids.• Wave-shifting fiber readout provides light collection uniformity

• Gaps between tiles are deliberately misaligned with the gaps between tracker towers and covered by scintillating fiber "tapes"



Design HeritageDesign Heritage

GLASTEGRET

ACD

Tracker

calorimeter

Dd

tracker

ACD

CsIcalorimeter

Backsplash reduced the EGRET effective area by 50% at 10 GeV compared to 1 GeV.

GLAST will be studying photons to above 300 GeV.

Anticoincidence Detector for GLAST is subdivided into smaller tiles to avoid the efficiency degradation at high energy.

0.2-2 MeV "backsplash" photons



Design ApproachDesign Approach

Lip to "hide" thermal blanket and micro-meteorite shield

Segmentation for side entry events



Science Requirement: EfficiencyScience Requirement: Efficiency

• SRD Background Rejection requirement: Contamination of the high latitude diffuse gamma rays by background in any decade of energy for > 100 MeV shall be less than 10%. The goal shall be 1%.

• Charged particle background rejection involves the use of pattern recognition in the tracker and the calorimeter as well as the ACD.

• For protons, calorimeter and tracker are powerful.• 105 : 1 at system level

• Electrons are more problematic.• Electrons create showers in the calorimeter identical with photon

showers. • Worst case is 3 x 103 : 1 at 10 GeV

• The required ACD efficiency for charged particles (detector efficiency + hermeticity) is 0.9997



Additional RequirementsAdditional Requirements

• Tile segmentation – Efficiency > 80% at 300 GeV relative to that at 1 GeV– Effective area at >60o; >0.1 of on-axis value

• No more than 10% loss of effective area – 6% in the plastic and structure– 1% from ACD deadtime– 1% loss from noise– <5% chance of loss of tile in 5 years (electronics)– <1% per year for loss of tile by micrometeoroid puncture



Physical interface specificationsPhysical interface specifications

• Mass 200 kg + 60 kg (30% reserve) = 260 kg• Electronics 34 kg + 17 kg (50% reserve) = 50 kg• Power 30 watts + 25 watts (80% reserve)• Volume - see materials presented by Martin Nordby• Electronic signals

– Fast VETO• Pre-primitives for Trigger thresholds• Hi Z trigger for calibration events

– Addresses of hit tiles• Pulse heights of hit tiles

– Rate date from all tiles– Housekeeping data– Command, command verification, and control



ACD Technical StatusACD Technical Status

• Detectors: • Scintillator tile light output tests have been performed. • Tile overlapping and detector tapes are planned to cover gaps • Electron background rejection analysis cuts being developed• Side tile segmentation is being reevaluated• Trade studies are being performed

• tile thickness, segmentation and PMT placement

• Electronics: • ASIC development proceeding

– First prototype submission was in January • Higher gain Hamamatsu PMTs are being evaluated• Electronic parts have been submitted for acceptance • High voltage power supply specs, SOW and cost estimate created

– Procurement for prototype sent to identified vendors

• Mechanical: • Tile support structure has been improved over proposal design



ACD WBS Organization ChartACD WBS Organization Chart

Alexander Moiseev, Lead

ACD Detectors4.1.6.3

Robert HartmanJohn Krizmanic

ACD Electronics4.1.6.4

Dave Sheppard, LeadS. Singh, ASIC design

Robert Baker

FabricationWilliam. DanielsDonald Righter

ACD Mechanical Components

4.1.6.5Thomas Johnson, Lead

Sharon SeipelScot Murphy

ACD Design and Science supportAlexander Moiseev,Lead

David Thompson, Robert HartmanDavid Bertsch, Jay Norris

ACD System Engineering

Tom Riley

ACD Subsystem4.1.6

Jonathan Ormes - Lead

ACD management4.1.6.1

Rudy Larsen - ManagerCristina Doria-Warner - Financial

ResourcesDennis Wicks - Scheduling

Electrical TestDarrin Buck

James Odom

ACD Flight Software4.1.6.6

Robert Schaefer, Lead

ACD SimulationsHeather KellyTaro Kotani

Alexander Moiseev

ACD Reliability and Quality Assurance4.1.6.2

Patricia. Huber, LeadRussell Murray, QualityJohn Remez, Reliability

Peter Jones, PartsFred Gross, Materials

Bo Lewis, Safety

Reserved4.1.6.7

Micrometeroid Shield /Thermal Blanket

4.1.6.BThomas Johnson, LeadLou Fantano, Thermal

LeadRobert Hartman

John Lindsay, LeadTom Johnson

Mission Integration & Test Support

4.1.6.9

John Lindsay, Lead

Mission Operation & Data Analysis

4.1.6.A

David Thompson, Lead

Insrument ACD Subsystem

Integration & Test 4.1.6.8

All ACD team members above are GSFC civil service employees or GSFC contractors



Contributing GSFC Lead OrganizationsContributing GSFC Lead Organizations• WBS 4.1.6 ACD Subsystem - Dr. Jonathan Ormes, GSFC Code 600, Space Science Directorate• WBS 4.1.6.1 ACD Management - Rudy Larsen, GSFC Code 700.1, Project Formulation

• System Engineering - Tom Riley, GSFC Code 730.4, Instrument Systems Office• Science Support- Dr. Alexander Moiseev, GSFC/USRA Code 661, Gamma Ray and Cosmic

Ray Astrophysics Branch• WBS 4.1.6.2 ACD Reliability and Quality Assurance - Patricia Huber, GSFC Code 303, Assurance

Management Office• WBS 4.1.6.3 ACD Detectors - Dr. Alexander Moiseev, GSFC/USRA Code 661• WBS 4.1.6.4 ACD Electronics - Dave Sheppard, GSFC Code 564, Microelectronics and Signal

Processing Branch• WBS 4.1.6.5 ACD Mechanical Components - Tom Johnson, GSFC Code 543, Mechanical

Engineering Branch• WBS 4.1.6.6 ACD Software - Bob Schaefer, GSFC/HSTX Code 664, Data Management and

Programming Office• WBS 4.1.6.8 Instrument Subsystem Integration & Test - John Lindsay, GSFC Code 568, Flight

Systems Integration and Test Branch• WBS 4.1.6.9 Mission I&T Support - John Lindsay, GSFC Code 568• WBS 4.1.6.A Mission Operations & Data Analysis - Dr. Dave Thompson, GSFC Code 661• WBS 4.1.6.B ACD Micrometeoroid Shield/Thermal Blanket - Tom Johnson, GSFC Code 543 /

Louis Fantano, GSFC Code 545, Thermal Engineering Branch------------------------------------------------------------------------------------------------------------------------------------

USRA- University Space Research Association EITI - Emergent Information Technologies Inc.



4.1.6 ACD Schedule

ActivityID

ActivityDescription

OrigDur

RemDur

EarlyStart

EarlyFinish

Gamma Ray Large Area Space Telescope4.1.6 ANTICOINCIDENCE DETECTOR

Subtotal 1,368 04/03/00 09/30/05+ 4.1.6.1 ACD MANAGEMENT

1,255 09/12/00 09/30/05+ 4.1.6.2 RELIABILITY & QUALITY ASSURANCE

1,176 01/11/01 09/30/05+ 4.1.6.3 ACD DETECTORS

593 11/07/00 04/04/03+ 4.1.6.4 ELECTRONICS

1,249 09/12/00 09/22/05+ 4.1.6.5 MECHANICAL COMPONENTS

776 12/01/00 01/26/04+ 4.1.6.6 ACD FLIGHT SOFTWARE

1,276 04/03/00 05/20/05+ 4.1.6.8 INSTRUMENT ACD SUB-SYSTEM I & T

1,100 01/11/01 06/14/05+ 4.1.6.9 MISSION INTEGRATION & TEST SUPPORT

1,100 01/11/01 06/14/05+ 4.1.6.B THERMAL BLANKET / MICRO SHIELD

1,100 01/11/01 06/14/05

FY00 FY01 FY02 FY03 FY04 FY05 FY06

INCOMPLETE



ACD Milestones

• ACD & Thermal Blanket Requirements Review 03/21/01• ACD & Thermal Blanket PDR 06/27/01• LAT Instrument PDR 08/06/01• ACD & Thermal Blanket CDR 06/26/02• LAT Instrument CDR 08/05/02• ACD Engineering Model (EM) Complete 05/15/03• ACD Flight Subsystem Assembly Complete 10/01/03• Thermal Blanket / Micrometeoroid Shield Ready for Integration 02/01/03 (with thermal model)• Delivery of Calibration Unit ACD to SLAC 05/15/03• Flight ACD Ready for Integration 01/26/04



Interim ACD Cost Estimate*

(Escalated K$)

*DOE/NASA funding.

4.1.6 ACD FY00 FY01 FY02 FY03 FY04 FY05 Total

GSFC (NASA) 436.2 607.1 3036.1 3136.2 1929.8 390.7 9536.1

Total 436.2 607.1 3036.1 3136.2 1929.8 390.7 9536.1



Technical Issues and Mitigations

• Increase technical margin for light collection– Add reflective termination to fibers or read out at both ends– Monitor and adjust PMT gain in flight– Request 25-30 kg additional mass for thicker tiles on top

• Required volume for electronics may exceed available– Place PMTs under ACD– Place some of electronics underneath the grid– Reduce side segmentation

• Parts acceptance and procurement– Prototype HVPS procurement is in preparation– Parts list submitted to Quality Assurance Branch

• Integration highly coupled to design– ACD I&T manager appointed to work with design team



Summary

• ACD team is in place and progress is quite rapid– Necessary trade studies underway

• Optimization of side segmentation• Optimization of redundancy• Optimization of light collection; tile thickness

– Requirements have been established

• Near term schedule advanced– Received additional funding for FY '01– Added staff to prepare for PDR– Draft Level 6 schedule is in hand

• Grass roots costing being scrubbed

ACD Subsystem

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