Internal Camera Review
October 14, 2008

Philosophy To Control Contamination Starts With
Understanding Each Individual Material Allowed In Cryostat
• Establish A Database of Permissible Materials and How They Must
Be Processed & Stored in Advance of Integration into Cryostat
– Materials Test Facility Provides The Input Data
• Provides outgassing species, outgassing rates (incl. temperature dependence), condensability, evaporability and impact on optical transmission
– Program:
• Study all Potential Materials (eg: NASA Database) & Their Preparation
• Study Coatings for Non-vacuum Friendly Materials
(eg: use of Parylene-C and HT on epoxy and electronics)
• Develop cleaning and handling procedures
• Create Database For Tracking All Components In Cryostat
– Individual materials tests and verification
– Sub-assembly tests and verification
– Tests and verification after shipping but before I&T at SLAC
– Tests during the buildup of the cryostat  no suprises since disassembly and cleaning would be a long process
LSST Internal Review
October 14, 2008
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• Material Test Facility Started Commissioning In July
–
Developing procedure for operating the chambers and protocol for measurements.
– Started making preliminary ROR measurements on some of the critical components:
• circuit board materials,
• epoxies in feedthroughs and connectors,
• effect of Parylene-C coating on adsorption
– Still assembling the cryogenic parts, so we have no data from the
QCM or optical transmission chamber yet.
• Started to Assemble the Database For Measuring Materials and
Tracking All Components In Cryostat
– Ultimately tells you what to expect from each subcomponent in cryostat --- and in particular, during the sub-integrations
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LSST Internal Review
October 14, 2008

Material Contamination Test Facility Schematic
LSST Internal Review
October 14, 2008
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Transport arm
Heater
Power supplies
Ion pump
Transport arm
Samples Exposed to
50%rh 24 hrs. (
D mass)
Samples Enter in A1
Baked & Pumped in C1
Sample moved to C2
Outgasses in C2
Measure Species and
Rate of Rise with RGA vrs temperature
Condensable Products
Deposited on cold Quartz
Microbalance
TC and
Instruments Condensible Products deposited on cold optical glass disk
Sample exits thru LL
Wobble stick
Scroll pump
Turbo pump
LSST Internal Review
October 14, 2008
Inert Gas
Delivery Glass disk moves to C3
Light Transmittance versus wavelength thru disk measured in C3
Re-evaporated condensables measured with RGA in C3
Glass disks enter and exit thru A3
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Rear view
CC Vac gauges
RGA units
Quartz
Crystal micro balance unit
LSST Internal Review
October 14, 2008
Turbopump manifold
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Snapshot: RGA during Outgassing of Polyimide/E-Glass sample at 84 ° C
Rate Of Rise (H
2
O)
& Bkd Curve at 79 0 C water
4x10 -8
9 cm 2 Polyimide E-
Glass Sample
Sample In: H
2
O
1.4x10
-9 Torr/sec
3x10 -8
H
2
2x10 -8
1x10 -8
Empty Chamber: H
2
O
8x10 -12 Torr/sec
N
2
CO
2
2x10 -9
LSST Internal Review
October 14, 2008
400 Seconds
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Outgas rate 55 °C
(torr-liters/sec/cm 2 )
Outgas rate 90 °C
(torr-liters/sec/cm 2 )
H
2
H
2
O
N
2
CO
2
6.2x10
-8
1.6x10
-8
1.7x10
-8
5.6x10
-9
3.7x10
-7
1.4x10
-7
1.5x10
-7
6.7x10
-8
*These Feedthroughs Are on the Back Flange and Operate
Close to Ambient Temperature
Surface area of epoxy Sample : 4.2 cm 2
LSST Internal Review
October 14, 2008
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Example of Sensitivity: Airborn Connector Body
• First Look At Our
Baseline Connector
Body Used Everywhere
--- Between Sensors,
FEE and RCC.
H
2
O
• Shows The Usual H
2
,
H
2
O and N
2 and CO
2
• But Also a set of spikes
– Possibly Sulphur
Dioxide (64+66)
H
2
N
2
CO
2
LSST Internal Review
October 14, 2008
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LSST Internal Review
October 14, 2008
10

•
All seals in the cryostat are double
O-ringed with pumpouts
• Divide cryostat into two vacuum regions (i) focal plane &
(ii) everything else
•
Connect them thru the lowest conductivity seals we can obtain
•
The GRID, GRID Shrouds, Cryoplate and FEE run at coldest temperatures.
•
The sensor surface is 10

20 0 C warmer than almost everything around it
– except L3. Its temp. is controlled by the raft-tower makeup heaters.
• Focal plane region sees L3, colder
GRID walls, GRID Shroud and the pumping chimneys. A 400l/sec TMP at rear gives ~130 l/sec at CCD’s
•
Everything else (BEE, Cables, MLI) is pumped by 2 nd TMP at ~400 l/sec
LSST Internal Review
October 14, 2008
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Pump path
Conductance: 195 l/sec
Eff. Pump speed: 130 l/sec
F.P. chimney connects front end vacuum region to pumping plenum — this is attached to the Cryo Plate
400 l/sec turbo pump
Sheet metal F.P. pumping plenum drops into Feedthrough Plate
LSST Internal Review
October 14, 2008
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•
The CCD surface should never be the coldest surface in the cryostat
•
During operation The CCD sensors will always be warmer (~10 0 C) than the surrounding materials that are most likely to outgas (FEE electronics, connectors, and cables)
• Before cooldown we envisage a long period of N
2 flushing the cryostat and pumping (at somewhat elevated temperatures) to reduce H
2
0 in the cryostat.
Additional pumping capacity during the initial pumpdown might be used.
•
Cooldown requires the Cryo plate be cooled with the FEE off but the makeup heaters on -- to keep the CCDs warmer than the FEE and GRID. We cool only within the allowed “survival range” of the FEE, before turning them on…and completing the cooldown.
•
If FEE electronics in a tower fails, the CCD & Raft Plate temperature drifts down in the tower. The makeup heaters should be adequate (and redundant) to avoid the CCD being over-cooled
LSST Internal Review
October 14, 2008
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• All material will be vacuum baked and stored in inert atmosphere prior to I&T. During I&T we will work in as dry/inert an atmosphere as is safe.
• We are selecting, processing and coating materials in the cryostat to reduce the uptake of H
2
0, CO/CO
2 during assembly and the subsequent desorption during operation
• Assuming we can reduce or eliminate all materials that produce other heavier condensables or contaminants that react chemically with the optical coatings, we will still be left with some residual slow - desorption of the usual condensibles molecules onto the focal plane. (Water etc…..)
• We are looking into the use of more passive pumping in the focal plane region to provide backup to the TMP’s, and/or mitigate the need to run them during observing.
LSST Internal Review
October 14, 2008
14

• Two Options Exist:
– “cold” evaporable getters that trap gases (zeolytes and charcoals)
–
Need to be tied to the GRID or Cryo-Plate
– Problem of containment and dusting in FP region
(eg: people have used 0.2 m m PTFE mesh)
–
Desorption during warmup
– need temp. control, isolatation or pumped
– “warm” non-evaporable getters that chemically break down gases
(NEG Pumps)
– commonplace in accelerators and electronics packaging
– Need to be kept “warmer” for better performance:
…. Eg: tied to the cryostat wall
• Both Options have (not insurmountable) problems
– Space in cryostat Focal Plane region
– Access to insert and replace materials near focal plane
• We want to understand from our materials testing, what we really will need, but are looking into these other options in parallel
LSST Internal Review
October 14, 2008
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LSST Internal Review
October 14, 2008
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A VERY OLD ESTIMATE OF OUTGASSING RATES
BASED ON EARLIER DESIGN AND MATERIALS
ZONE MATERIALS
Metals/Glass/ Ceramic
Focal
Plane Coated PCB's/ Plastics
Metals/Glass/ Ceramic
GRID and
FEE Super Insulation
Cu Thermal Straps
Coated PCB's/ Plastics
BEE Metals/Glass/ Ceramic
Super Insulation
Coated PCB's/ Plastics
EXPOSED
AREA
OUT GASSING m 2
4.7
0.89
18
10 -6 Torr-L/sec
907
3
10602
263
11280
7.9
12
178
7.3
LSST Internal Review
October 14, 2008
293
122
5761
0.28
220
2468
PRESSURE
(10 Hrs @500 L/s)
Torr
1.8E-06
3.4E-05
5.4E-06
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C1 inside view
Samples come in from A1 on mag.
transport arm
Heaters (2)
Samples proceed to C2
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LSST Internal Review Thermocouples (2)

C2 inside view
RGA
Samples enter from C1
Cold strap
Glass disk stage
Quartz balance
(crystal is under stage)
Heaters (2)
Sample boxes enter and exit thru A2
“Wobble stick”
Sample box
LSST Internal Review
Thermocouples (3) refrigerant loop
Glass disks come in from C3 clean and go back dirty
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C3 inside view
To C2
Refrigerant loop
Cold strap
Cold strap bent down in “U” to allow motion
Actuator piston moves basket back and forth
Thermocouple (1)
Glass disks come in and go out thru A3
Light beam comes up thru bottom, passes thru disks and is detected above
LSST Internal Review
October 14, 2008
“wobble stick” double glass disk stage
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Glass Disk Holder and Sample Box
Glass Disk Holder
(clamps glass and sits snuggly in baskets)
LSST Internal Review
October 14, 2008
Sample box
(sliding lid and
22
2 holes for outgassing)

Optical setup overview
Repeated with each of 6 band passes:
- 400 nm
- 500 nm
- 600 nm
- 750 nm
- 850 nm
- 1000 nm LSST Internal Review
October 14, 2008 detector diode mounted here
Light source
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Optical setup box
TO C3 aperture
Beam splitter
Reference diode
LSST Internal Review
October 14, 2008
Filter wheel
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Final picture: some peripherals
Vacuum oven 50% RH environment microbalance
LSST Internal Review
October 14, 2008
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INSTRUMENTATION FOR 3 rd OPTICAL TRANSMISSION CHAMBER
Contaminated & Reference Samples Moved (Cold) From 2 nd Chamber
White Light  Monitor Diode & Window  Filter Wheel (LSST)  Cold Sample
Slide or Uncontaminated Slide  Window  Precision Photodiode/PM. Diode
Temporal Stability of Light Source Calibrated Out Using Monitor Diode
Piston Moves Samples Back & Forth In Vacuum Thru Same Optical Path to
Interleave Measurements (Avg. Out Instabilities in Light Output & Light Path)
Observe <0.1% sensitivity: comparable to photometric target
LSST Internal Review
October 14, 2008
Measurements
Sequenced By
Computer (~0.1 Hz) and Recorded and
Analyzed
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RESULTS FROM TESTS OF OPTICAL TRANSMISSION
CHAMBER
400nm 500nm 600nm
750nm 850nm 1000nm
0.02%
DISTRIBUTION OF MEANS OF 120 EXPERIMENTS
(@1000 samples) TAKEN OVER ~20 MINUTES
ERROR AS A PERCENT OF MEAN (DURING 20min)
LSST Internal Review
October 14, 2008
TARGET < 0.1%
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