LSST Camera Cryostat Design & Integration

DOE Program ReviewSLAC

June 2006

Rafe H. SchindlerExperimental Group E - SLAC

DOE Review

June 2006 SLAC

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Overview

• SLAC Is Responsible for The Major Mechanical Components & The Final Integration & Testing of the LSST Camera:

– RAFTS – BACK END ELECTRONICS – OPTICAL ELEMENTS – CRYOSTAT & FOCAL PLANE– CAMERA BODY MECHANISMS– UTILITIES (Thermal/Vacuum/Contamination)

• Will Discuss The Cryostat Design and SLAC R&D. Then Briefly the Cryostat Assembly Sequence

CRYOSTAT REQUIREMENTS

GRID PROPERTIES

METROLOGY

ASSEMBLY AND TEST

SLAC DELIVERABLES

Integration & Testing of Camera

DOE Review

June 2006 SLAC

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LSST Cryostat Design, Assembly & Test

REQUIREMENTS COMBINE:

• Mounting of Close-Packed Rafts & Ancillary Sensors Onto GRID -- Maintaining Overall Flatness (~10 um)

• Rapid Sub-m Metrology to Verify Focal Plane Flatness During Assembly

– From 200C -1000C in All Orientations and Through Optics

• Fast XY Actuation of GRID For Tracking– ~100 um Motion at ~10’s Hz

• Dissipation of ~1KW Internal Heat From Electronics & Radiation Thru L3

• Maintaining Thermal Uniformity Across Sensors (0.3 0C) For QE

– Vac Vessel (10-6 Torr) with Large Window

• Control Contamination Onto The Cold FPA

One of the More Challenging Engineering Tasks

DOE Review

June 2006 SLAC

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Focal Plane Flatness Budget

Sensor Module

5m p-v flatness over entire sensor surface

Raft Assembly

6.5m p-v flatness over entire surfaces of sensors

Focal Plane Assembly

10m p-v flatness over entire surfaces of sensors

(at -100 0C & All Camera Orientations)

Before FPA I&T

A Few Microns For Mechanical Reproducibility, Gravity, and Thermal Distortions

DOE Review

June 2006 SLAC

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Focal Plane Design Philosophy To Achieve Metrological Goals

Build Precision Into The GRID and the RAFTS In Advance Allowing Fast “Snap Together” Assembly of Focal Plane:

• Make GRID a Thermally & Mechanically Passive Structure

» Use Si Carbide For High Stiffness & Conductivity and Low Thermal Expansion (matched to Al Nitride).

» Isolate It To Minimize Heat Flow & Distortion

< 0.3 m Gravity Sag and <0.2m Sagitta for T~10C

• Make RAFTS Interchangeable Without Further Adjustment

» Use 3-Vee kinematic coupling with sub-m repeatability

» Setup Rafts relative to their kin. mnts on same metrology fixture

» Pre-load GRID & Adjust Kin. Mnt. Balls on GRID To Accept Standard Raft at Ambient Temp.

THIS SHOULD OBVIATE NEED TO FUTHER ADJUST RAFTS DURING I&T

DOE Review

June 2006 SLAC

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Raft Metrology Fixture Embodies Desired Geometry Needed on Grid

FEE Cage

Raft

Flat and parallel to 3

balls ~100 nm

Raft Metrology

Fixture

Set up detectors coincident to the flat surface of the fixture

Raft and GRID Metrology Strategy To Speed Assembly

AT BNL

DOE Review

June 2006 SLAC

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Kinematic Mounting Points On The GRID Are Measured & Adjusted to Mimic Raft Metrology Fixture

During Assembly of Focal Plane, a Motion Stage Lifts Raft Onto GRID Kin. Mounting Points From Behind

Thermal Connections Are Made

Metrological Verification Follows Immediately (see following slides)

GRID

GRID

Cold PlateCold Plate

FEE Cage

Raft

Metrology Strategy To Simplify RAFT Assembly onto GRID

AT SLAC….

DOE Review

June 2006 SLAC

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PRACTICAL REALIZATION OF THIS MOUNTING & METROLOGY SCHEME

BALLS MOUNTED IN GRID

SPRING TO LOAD KINEMATIC MOUNT TO GRID

3-Vee BLOCKS ON RAFT To Mount RAFT to GRID

ADJUSTORS FOR EACH SENSOR’S KIN. MNT. TO AlN RAFT BASE

~12cm

DOE Review

June 2006 SLAC

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Metrology Techniques Under Evaluation To Verify and Monitor Focal Plane Flatness

• During RAFT Insertion, Flatness Must Be Measured At Ambient Temperature to <<0.5m Across ~65cm Diameter Focal Plane

• When Cryostat Sealed With L3 Must Be Re-Measured Under Vacuum and Cold

– Investigating Non-Contact Laser Displacement Heads as the Primary Tool

• Also Evaluating “In-Situ” Methods To Allow On-Demand Measurements of Changes in the FPA Independent of Camera and Telescope Optics

– Capacitive Edge Sensors (Rafts)

– Diffraction Pattern Generator (Sensor Surface + Rafts)

Allow Fast Diagnostic Verification of FPA Alignment in all Orientations

Non-Contact Laser Displacement Heads For Metrology During Assembly

L3 or WINDOWFOCAL PLANE

OPTICAL REF. FLAT

TRIANGULATION HEAD

LASER TRIANGULATION HEADXY STAGE

SHOWN UPSIDE DOWN

Two Commercial Laser Displacement Heads Mounted in Opposing Directions on XY Stage

One Looks Down at Optical Reference Flat

The Other Looks Up at Focal Plane

Sum of the Two Displacements Removes Most XY Stage Errors

Sub-m Metrology Can Be Done Rapidly By Stitching Smaller Overlapping Areas

DOE Review

June 2006 SLAC

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Test of Non-Contact Displacement Heads

Sensor Head Sensor Head (LK-G15)(LK-G15)

Sensor Sensor Head Head (LK-G37)(LK-G37)

Optical FlatOptical Flat(reference(reference))

SiC SiC SampleSample

XY Actuation XY Actuation StageStage

Dual Dual ControllerController

12cm

DOE Review

June 2006 SLAC

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Displacement Sensor Test – Measurement of Polished Silicon Carbide Sample

~0.2 m

RE

SID

UA

LS

DISTANCE ALONG SiC SURFACE

1 m

FORWARD SCAN

BACKWARD SCAN

TEST AT SLAC

DOE Review

June 2006 SLAC

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Dual sensor XY carriage

Inspection Opt. Table

Assy Opt. Table

Reference surface XY carriage

Camera Focal Plane GRID

Displacement sensors (up & down looking)

Bottom View Shows Partial Population of Focal Plane Array

FPA STITCHING METROLOGY IN PRACTICE

Cryostat Open For Raft Insertion

Take Rapid Measurements After Each Insertion

Multiple Overlapping Samples With Translated Reference Flat Used to Stitch Together the Large Surface

DOE Review

June 2006 SLAC

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Stitching Metrology Strategy - Simulation

• Fidelity of Measurement Is Trade-Off Between Speed and Completeness

• Simulation Used To Determine Metrology Strategy and Approach:

Monolithic reference (eg granite surface & air bearing) versus localized sampling (smaller ref. flat)

Sample 65cm Diam. Focal Plane With a 20cm Flat

Propagated Error Distributions Compared to Input errors. Four Simulations (2x Different Grid Spacings and 2x Ref. Separations)

Input Error

3mm Spacing

10mm Spacing1.5 Radii Separation

1.2 Radii Separation

DOE Review

June 2006 SLAC

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STARTUP OF METROLOGY TEST LAB

Polycold dual circuit, recirculating cryo-cooler (1.5 kW cooling capacity @ -120ºC) – just arrived

Vacuum chamber for Cold Metrology (cryogenic thermal control & optical quality inspection window)

TEST CHAMBER

TURBO PUMP

RGA

OPTICAL WINDOW

XY STAGE

TEMP. & PRESS. CNTRLS

DOE Review

June 2006 SLAC

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In-Situ Metrology: Diffraction Pattern Generator

• Measure FPA Flatness Directly by Centroiding …Ellipses & Measuring Deviations of Known Pattern

• Centroiding Digital Images off Silicon Gives a <<1m on CCD Piston

Laser & Grating

Silicon Wafer

Raft

Grant Awarded at Stanford Nanofabrication Facility To Pursue Grating Fabrication Techniques

• Goal: Shorter spots, increased density & uniform intensity

CCD Imaged Ellipse

In-Situ Metrology: Capacitive Edge Sensors

• Measure Raft Alignment and Piston Directly

SIMPLEST IMPLEMENTATION:

• Conductive Pads Printed on Rafts & GRID

• Digitizing Chip Mounted Near Pads

• Measure Raft Piston and/or XY At Each Corner

SLAC R&D WITH THIS CHIP:

• Full Size Prototype With AD4766 Chip

• Chip Tested In Lab at -1200C

• Noise Limited To ~20 nm For Our Typical Displacements (~200m)

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DOE Review

June 2006 SLAC

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Cryostat Assembly Sequence – Designed For Tests & Arbitrary Removal Of Rafts For Repair/Replacement

SiliconCarbide

Grid

Fast Actuators

Cryo Plate

Cool Plate

Feedthrough Flange

Outer Cylinder

INSTALL GRID+ACTUATORS+CRYO PLATES INTO CLEAN & EMPTY BODYINSTALL GRID+ACTUATORS+CRYO PLATES INTO CLEAN & EMPTY BODY

ADD RAFT DUMMY LOADS & TEST FAST ACTUATION SYSTEMADD RAFT DUMMY LOADS & TEST FAST ACTUATION SYSTEM

ADD BLANKOFFS & TEST VACUUM & THERMAL SYSTEMSADD BLANKOFFS & TEST VACUUM & THERMAL SYSTEMS

VERIFY CONTAMINATION SPECIFICATIONS VERIFY CONTAMINATION SPECIFICATIONS

DOE Review

June 2006 SLAC

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RAFT LOADING SEQUENCE – IN ANY BAY

WORKING UPSIDE DOWN IN CLEAN ROOM:WORKING UPSIDE DOWN IN CLEAN ROOM:

REMOVE DUMMY LOAD IN BAY & INSTALL INSULATIONREMOVE DUMMY LOAD IN BAY & INSTALL INSULATION

ALIGN & SUPPORT RAFT FROM BACKSIDE WITH ROBOTALIGN & SUPPORT RAFT FROM BACKSIDE WITH ROBOT

INSTALL ONTO GRID’S KINEMATIC MOUNTS INSTALL ONTO GRID’S KINEMATIC MOUNTS

DOE Review

June 2006 SLAC

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WARM METROLOGY

PULL DOWN RAFT ONTO KINEMATIC MOUNTS ON GRIDPULL DOWN RAFT ONTO KINEMATIC MOUNTS ON GRID

MAKE UP THERMAL CONNECTIONS TO CRYO PLATE # 1MAKE UP THERMAL CONNECTIONS TO CRYO PLATE # 1

VERIFY SURFACE FLATNESS – WARM – USING METROLOGY HEADSVERIFY SURFACE FLATNESS – WARM – USING METROLOGY HEADS

DOE Review

June 2006 SLAC

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INSTALL BACK-END ELECTRONICS

ATTACH BEE CARDS TO FLEX CABLE - TAKE UP SRVC LOOPATTACH BEE CARDS TO FLEX CABLE - TAKE UP SRVC LOOP

MAKE UP THERMAL CONNECTIONS TO BEE CAGEMAKE UP THERMAL CONNECTIONS TO BEE CAGE

ATTACH FO CABLE TO FEEDTHROUGH & TESTATTACH FO CABLE TO FEEDTHROUGH & TEST

DOE Review

June 2006 SLAC

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REPEATFOR ALL BAYS

REPEAT METROLOGICAL & FULL ELECTRONIC TESTING – COLD REPEAT METROLOGICAL & FULL ELECTRONIC TESTING – COLD PROCEED TO INTEGRATE CRYOSTAT WITH CAMERA BODYPROCEED TO INTEGRATE CRYOSTAT WITH CAMERA BODY

CLOSE CRYOSTAT WITH L3 & REAR BULKHEAD CLOSE CRYOSTAT WITH L3 & REAR BULKHEAD VACUUM & THERMAL PROCESS THE CRYOSTAT – CHECK CONTAMINATIONVACUUM & THERMAL PROCESS THE CRYOSTAT – CHECK CONTAMINATION

DOE Review

June 2006 SLAC

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CONCLUSIONS

• EXCELLENT PROGRESS DEVELOPING AN INTEGRATED CRYOSTAT & FOCAL PLANE DESIGN TO MEET SCIENCE REQUIREMENTS:

– VIABLE STRATEGIES FOR:

– ASSEMBLY & REPAIR – RAFT AND FOCAL PLANE METROLOGY– THERMAL CONTROL OF SENSORS AND RAFTS

• DEVELOPING MORE DETAILED DESIGN FOR VACUUM, THERMAL AND CONTAMINATION CONTROL OF CRYOSTAT AS A SYSTEM AS WELL AS THE ACTUATION OF THE GRID

• R&D TO VERIFY METROLOGY TECHNIQUES PROCEEDING

• R&D TO STUDY CONTAMINATION ISSUES & MATERIALS CONTROL STARTING UP

DOE Review

June 2006 SLAC

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SPARE SLIDES

DOE Review

June 2006 SLAC

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Dual sensor XY carriage

Inspection Opt. Table

Assy Opt. Table

Reference surface XY carriage

Rear Bulkhead Closed

Displacement sensors (up & down looking)

Metrology of FPA Under Vacuum and Cold

Displacement Sensor Measures FPA Through Vacuum Barrier Window.

Cryostat Body

Cryostat Closed With Vacuum Window or L3 and Cooled To Operating Temp.

Metrology Repeated [Applying Small Optical Corrections]

DOE Review

June 2006 SLAC

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Simplify Metrology By Use of Silicon Carbide

• Significantly Better Structural and Thermal Properties Than Metals

– Expect ~ 1/3 m Sag Under Gravity & < 0.5 m From Thermal Distortion

• Good CTE Match To Al Ni In Rafts

Support Support

Support

1 G Sag of Loaded GRID

Focal Plane Assembly Unit Alum. Steel Invar 36 SC-30Total mass with rafts (25 kg) kg 100 237 246 112P-V gravity sag over aperture

0-90 elevation angle m 1.350 1.030 1.400 0.25030-90 elevation angle m 0.675 0.515 0.700 0.12545-90 elevation angle m 0.395 0.302 0.410 0.07360-90 elevation angle m 0.181 0.138 0.188 0.033

Mode shape and frequencyMode 1, torsion/twist Hz 205 219 184 463Mode 2, X translation Hz 241 261 217 546Mode 3, Y translation Hz 339 384 321 775Mode 4, Z translation Hz 366 413 346 846

Elastic modulus / density SI 25.56 25.00 17.67 130.16Thermal conductivity / CTE SI 10.00 4.69 8.08 75.00

DOE Review

June 2006 SLAC

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Stitching Metrology Checkout (3)

• Top: 4 separate realizations of resulting surface figure error propagation, depending on grid spacings and number of intermediate reference locations.

• Bottom: demonstration of recovering an input aspherical term to 1% of its “true” value (using a 200mm diameter reference to map a 640mm diameter focal plane.

DOE Review

June 2006 SLAC

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PROTOTYPE LASER PROJECTOR HEAD THAT WOULD BE MOUNTED ON GRID

2.00"0.75" 0.3930"

0.37"1.07"

1.57"0.15"

1.25"

0.83"

0.95"

0.35"

0.75"

0.65"0.22"

0.83"

0.95"

0.28"

1.00"

CONSTRUCTED UTILIZING STABILIZED SINGLE MODE FIBER COUPLED DIODE LASER, DIFFRACTIVE & FOCUSSING ELEMENTS

PROJECTOR HEAD

DIODE LASER

DOE Review

June 2006 SLAC

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IMPROVEMENTS ADDRESSING REMAINING PROBLEMS

• ELONGATED ELLIPSES:

• INCREASE DENSITY TO BETTER UTILIZE GRID REAL ESTATE:

ADD FOCUSSING ELEMENT AFTER DIFFRACTIVE ELEMENT

Lens

Laser

Diffractive beam splitterCrossed gratings

ADD BEAM SPLITTER AFTER FOCUSSING ELEMENT

OR DEVELOP CUSTOMIZED MICROMACHINED DIFFRACTIVE ELEMENTS

DOE Review

June 2006 SLAC

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OPTIMIZED MICROMACHINED 2D ARRAY OF APERTURES

Layout for chrome-on-glass diffraction grating with electron beam etched apertures being produced at Stanford in June 2006

Lens

Laser

Micromachined diffraction grating

Laser generates array of spots with relatively uniform amplitudes if apertures ~

Pattern from 0.5 micron diameter circular apertures on a grid of 150 columns per mm and 50 rows per mm.

Awarded Grant at Stanford Nanofabrication Facility To Pursue Grating Fabrication Techniques

DOE Review

June 2006 SLAC

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CABLE TO BACK ANNULAR FLANGE

ATTACH FIBER OPTIC & FLEX CABLES TO REAR FLANGE FTATTACH FIBER OPTIC & FLEX CABLES TO REAR FLANGE FTINSTALL OTHER ELEMENTS INSTALL OTHER ELEMENTS

Guide, SH SensorsGuide, SH SensorsTemperature Monitoring & ControlTemperature Monitoring & ControlIn-Situ Metrology, Fe55 Source, Service Cables…In-Situ Metrology, Fe55 Source, Service Cables…

TEST CONNECTIONSTEST CONNECTIONS

DOE Review

June 2006 SLAC

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Camera Integration and Test Sequence

SENSOR ACCEPTANCE TESTFunctional + Metrological (warm)

RAFT ACCEPTANCE TESTMetrological (warm)

RAFT TOWER ACCEPTANCE TESTFull Functional + Thermal + Metrological(warm and cold) + Contamination(?)

FEE

Si CCD Sensor

Raft Structure

Raft Assembly

Flex Cable &

FEE Cage

Thermal Strap(s)

Sensor Packages

CCD Carrier

Thermal Strap(s)

DOE Review

June 2006 SLAC

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Camera Integration and Test Sequence

CRYOSTAT BODY ACCEPTANCE TESTVacuum Processing, Contamination, Plumbing, Thermal Controls, FPA Actuation

FOCAL PLANE ASSEMBLYMetrological (warm), Limited Functional Testing of Sensors & Electronics

Grid

Cryo PlateImage Stabilization Actuators

Outer Cylinder

Tested Raft Towers

BEE (not shown)

Sensors Not Shown:GuideShack HartmanCurvature

Temp. Install L3 WindowOr Blankoff

Raft Towers

Temp. install Cryostat Back Plate

Back Flange

DOE Review

June 2006 SLAC

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Camera Integration and Test Sequence

CRYOSTAT & FPA ACCEPTANCE TEST• Metrological (warm, cold), Vacuum Processing,Contamination, Sensor Thermal Controls, Full Actuation, Full Sensor & Electronics Functional Tests

• Use In-Situ Systems To Verify Metrology In All Orientations & Following Actuation

Cryostat Rear Bulkhead

Focal Plane (one raft shown)

L3 and/or Window

Not Shown:BEE And Cables to Bulkhead Flange Other Misc CablesElements of Thermal SystemElements of Vacuum SystemIn-Situ Metrology SystemsX-Ray Source Calibration System

Cryostat Body

DOE Review

June 2006 SLAC

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Camera Integration and Test Sequence

CAMERA BODY & MECHANISMS ACCEPTANCE TESTSMech.Functionality, Contamination

CAMERA MECH. FUNCTIONALITYACCEPTANCE TEST

Base Plate

Shutter (temp. install)

Filter Changer, (temp. install)

Camera Housing

Filter Carousel, with Dummy Filters

Cryostat Assembly With L3

•Electrical Integration

•Plumbing Integration -thermal system -vacuum system -purge system

Shutter

Functional Tests Power & ConditioningExposure Control Elect.FP Control Elect.Vacuum /Purge Control Elect.Thermal Control Elect.

Filter Changer

Utilities Frame

DOE Review

June 2006 SLAC

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Camera Integration and Test Sequence

CAMERA CALIBRATIONS AND FINAL ACCEPTANCE TEST

L1/L2 Assembly

Filters on Carousel

Camera CalibrationsSee Talk: David Burke

Filter in use

LOAD FILTERS

ADD L1/L2