GLAST LAT Project March 24, 2003

3B Tracker Peer Review, WBS 4.1.4 1

GLAST Large Area Telescope:GLAST Large Area Telescope:

Tracker SubsystemWBS 4.1.4

3B: EM Mini-Tower

Robert JohnsonSanta Cruz Institute for Particle PhysicsUniversity of California at Santa CruzTracker Subsystem Manager

johnson@scipp.ucsc.edu

Gamma-ray Large Gamma-ray Large Area Space Area Space TelescopeTelescope

GLAST LAT Project March 24, 2003

3B Tracker Peer Review, WBS 4.1.4 2

Mini-Tower ObjectivesMini-Tower Objectives

• Develop and test tray assembly procedures with real electronics and detectors.

• Test the readout electronics in a realistic environment.• Test the detector system with minimum-ionizing particles (cosmic

rays).• Exercise the TEM based readout with multiple layers and multiple

cables.• Platform for development of Tracker subsystem test procedures and

software that will be needed for flight-module production.• Platform for I&T preparations.

• Note: this device is not intended to be used for environmental testing, mechanical or thermal.

GLAST LAT Project March 24, 2003

3B Tracker Peer Review, WBS 4.1.4 3

Mini-Tower ConfigurationMini-Tower Configuration

• The essence: – 3 instrumented x,y silicon-strip detector planes– Each x,y plane is preceded by a thin tungsten foil (3% rad. len.)

• The details:– 4 light composite panels supporting SSD ladders– 1 bottom tray with no SSD but with the mechanical interface to

the grid • This is an older prototype tray refitted by COI with preliminary

versions of the titanium reinforcement

– 8 short versions of the readout cables– 8 MCMs (2 for each pair of readout cables)

• The 2 lowest MCMs have no SSDs connected but are required in order to complete the data transmission circuit

– Inexpensive aluminum walls

GLAST LAT Project March 24, 2003

3B Tracker Peer Review, WBS 4.1.4 4

Extra Functional TrayExtra Functional Tray

• Another tray, instrumented on both sides with SSD and electronics, plus thin converter foils, is being assembled in Italy. This is in addition to the Mini-Tower.

• This tray will undergo complete environmental testing to qualification levels, including– Random vibration: GEVS (LAT-TD-01004)– Thermal vacuum: 30C to +50C (LAT-TD-01037)

• This will complement the environmental testing of the mechanical-thermal tower module, which will not include functional detectors and electronics.

GLAST LAT Project March 24, 2003

3B Tracker Peer Review, WBS 4.1.4 5

Mini-TowerMini-Tower

Al “grid” fixture

GLAST LAT Project March 24, 2003

3B Tracker Peer Review, WBS 4.1.4 6

Mini-Tower Bottom TrayMini-Tower Bottom Tray

• Refurbished extra bottom tray from the prototype mechanical tower• Titanium and carbon-fiber reinforcement added by COI (intermediate

design between the prototype tower and the final Hytec design).

Vibration fixture frame

Bottom face of the bottom tray

Titanium corner reinforcement and flexure blade

Stainless Steel

GLAST LAT Project March 24, 2003

3B Tracker Peer Review, WBS 4.1.4 7

Mini-Tower ElectronicsMini-Tower Electronics• 13 functional MCMs were assembled at Teledyne.• 6 are in the mini-tower, and 2 more will be on the tray destined for

environmental testing.• 2 of them are shown below, in protective cases, connected to 2 Mini-Tower

readout cables (via connector savers). The cables are connected to a TEM module.

GLAST LAT Project March 24, 2003

3B Tracker Peer Review, WBS 4.1.4 8

Mini-Tower TrayMini-Tower Tray

One of the functional EM trays, inside its service box.

GLAST LAT Project March 24, 2003

3B Tracker Peer Review, WBS 4.1.4 9

Leakage currentsLeakage currents

TG001 Back leakage current

0

500

1000

1500

2000

2500

3000

3500

0 20 40 60 80 100 120

Bias Voltage (V)

Leak

age

curr

ent (

nA)

Tray-lab

Expected (sum ofladderscurrents)

Leakage current remains within specifications for all tested trays (no damage during assembly).

The leakage current measured on full trays is in most cases lower than the sum of the single-ladder currents (but ladders were tested at 22º average temperature, while trays were tested at 17.5 º).

GLAST LAT Project March 24, 2003

3B Tracker Peer Review, WBS 4.1.4 10

Grounding ConsiderationsGrounding Considerations

Handles for assembly/storage fixtures

MCM ground point (1 of 3), required scraping off conformal coat

Initially the aluminum honeycomb core was floating, resulting in a huge increase of noise when trying to ground the box containing the tray.

Good ground electrical contact (handles-honeycomb and MCM-honeycomb) was accomplished through long screws that touch the honeycomb (as was always in the specification). This solved all grounding-related noise problems.

GLAST LAT Project March 24, 2003

3B Tracker Peer Review, WBS 4.1.4 11

Noise Trigger RateNoise Trigger Rate

Threshold scan FE 21

0,01

0,1

1

10

100

1000

10000

100000

0 10 20 30 40 50 60

Threshold DAC

Co

un

tin

g r

ate

(H

z)• The noise trigger rate is monitored for each FE chip as a function of

discriminator threshold.• Residual triggers at high threshold are due to cosmic rays.

OR of 64 Channels

GLAST LAT Project March 24, 2003

3B Tracker Peer Review, WBS 4.1.4 12

Masking Noisy Channels: TS001Masking Noisy Channels: TS001

Threshold Scan @ 115 VThreshold Scan @ 115 Vwith 7 noisy strips masked

With the 7 noisy strips (<0.5%) masked, the behavior of the counting rate as a function of threshold is quite uniform over the whole tray.

GLAST LAT Project March 24, 2003

3B Tracker Peer Review, WBS 4.1.4 13

Pitch Adapter IssuesPitch Adapter Issues

Threshold Scan at 115 V with 6 noisy strips masked.

Problems with the pitch adapters used by Teledyne for the functional EM MCMs resulted in sections of some MCMs in which most strips could not be wire bonded to the SSDs. This leaves holes in the coverage, as illustrated below. This problem with the pitch adapter design has been resolved (Presentation 6E).

Region of bad pitch-adapter alignment.

GLAST LAT Project March 24, 2003

3B Tracker Peer Review, WBS 4.1.4 14

Ruthenium Ruthenium Source Profile Source Profile

Some noisy strips masked.

TG001 Front

GLAST LAT Project March 24, 2003

3B Tracker Peer Review, WBS 4.1.4 15

Cosmic Ray TriggersCosmic Ray Triggers

Number of fired strips per event. Number of clusters per event.

TS001 Front