Transcript GLAST Large Area Telescope: Tracker Subsystem 3B: EM Mini-Tower WBS 4.1.4

GLAST LAT Project
March 24, 2003
GLAST Large Area Telescope:
Gamma-ray Large
Area Space
Telescope
Tracker Subsystem
WBS 4.1.4
3B: EM Mini-Tower
Robert Johnson
Santa Cruz Institute for Particle Physics
University of California at Santa Cruz
Tracker Subsystem Manager
[email protected]
3B
Tracker Peer Review, WBS 4.1.4
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GLAST LAT Project
March 24, 2003
Mini-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.
3B
Tracker Peer Review, WBS 4.1.4
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GLAST LAT Project
March 24, 2003
Mini-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
3B
Tracker Peer Review, WBS 4.1.4
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GLAST LAT Project
March 24, 2003
Extra 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: 30C to +50C (LAT-TD-01037)
• This will complement the environmental testing of the mechanicalthermal tower module, which will not include functional detectors and
electronics.
3B
Tracker Peer Review, WBS 4.1.4
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GLAST LAT Project
March 24, 2003
Mini-Tower
Al “grid” fixture
3B
Tracker Peer Review, WBS 4.1.4
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GLAST LAT Project
March 24, 2003
Mini-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
Titanium corner reinforcement
and flexure blade
Bottom face of
the bottom tray
Stainless
Steel
3B
Tracker Peer Review, WBS 4.1.4
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GLAST LAT Project
March 24, 2003
Mini-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.
3B
Tracker Peer Review, WBS 4.1.4
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GLAST LAT Project
March 24, 2003
Mini-Tower Tray
One of the functional EM trays, inside its service box.
3B
Tracker Peer Review, WBS 4.1.4
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GLAST LAT Project
March 24, 2003
Leakage currents
Leakage current remains within specifications for all tested trays
(no damage during assembly).
TG001 Back leakage current
3500
Tray-lab
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).
3000
Expected (sum of
ladderscurrents)
Leakage current (nA)
2500
2000
1500
1000
500
0
0
20
40
60
80
100
120
Bias Voltage (V)
3B
Tracker Peer Review, WBS 4.1.4
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GLAST LAT Project
March 24, 2003
Grounding Considerations
Initially the aluminum honeycomb core was floating, resulting in a huge
increase of noise when trying to ground the box containing the tray.
Handles for
assembly/storage
fixtures
MCM ground point
(1 of 3), required
scraping off
conformal coat
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.
3B
Tracker Peer Review, WBS 4.1.4
10
GLAST LAT Project
March 24, 2003
Noise Trigger Rate
• 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.
Threshold scan FE 21
100000
10000
OR of 64 Channels
Counting rate (Hz)
1000
100
10
1
0,1
0,01
0
10
20
30
40
50
60
Threshold DAC
3B
Tracker Peer Review, WBS 4.1.4
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GLAST LAT Project
March 24, 2003
Masking Noisy Channels: TS001
Threshold Scan @ 115 V
Threshold Scan @ 115 V
with 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.
3B
Tracker Peer Review, WBS 4.1.4
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GLAST LAT Project
March 24, 2003
Pitch Adapter Issues
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).
Threshold
Scan at 115 V
with 6 noisy
strips masked.
3B
Region of bad
pitch-adapter
alignment.
Tracker Peer Review, WBS 4.1.4
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GLAST LAT Project
March 24, 2003
Ruthenium  Source Profile
TG001 Front
Some noisy strips masked.
3B
Tracker Peer Review, WBS 4.1.4
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GLAST LAT Project
March 24, 2003
Cosmic Ray Triggers
TS001 Front
Number of fired strips per event.
3B
Number of clusters per event.
Tracker Peer Review, WBS 4.1.4
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