LSST Camera Cryostat Design & Integration DOE Program Review SLAC June 2006 Rafe H. Schindler Experimental Group E - SLAC

DOE Review June 2006 SLAC 2 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 3 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 20 0 C  C 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 (  C) 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 4 Focal Plane Flatness Budget Sensor Module 5  m p-v flatness over entire sensor surface Raft Assembly 6.5  m p-v flatness over entire surfaces of sensors Focal Plane Assembly 10  m p-v flatness over entire surfaces of sensors (at C & All Camera Orientations) Before FPA I&T A Few Microns For Mechanical Reproducibility, Gravity, and Thermal Distortions

DOE Review June 2006 SLAC 5 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 <0.2  m Sagitta for  T~1 0 C 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 6 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 7 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) GRIDGRID GRIDGRID Cold Plate FEE CageRaft Metrology Strategy To Simplify RAFT Assembly onto GRID AT SLAC….

DOE Review June 2006 SLAC 8 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 9 Metrology Techniques Under Evaluation To Verify and Monitor Focal Plane Flatness During RAFT Insertion, Flatness Must Be Measured At Ambient Temperature to <<0.5  m 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 WINDOW FOCAL PLANE OPTICAL REF. FLAT TRIANGULATION HEAD LASER TRIANGULATION HEAD XY 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 11 Test of Non-Contact Displacement Heads Sensor Head (LK-G15) SensorHead(LK-G37) Optical Flat (reference ) SiCSample XY Actuation Stage DualController 12cm

DOE Review June 2006 SLAC 12 Displacement Sensor Test – Measurement of Polished Silicon Carbide Sample  ~0.2  m RESIDUALS DISTANCE ALONG SiC SURFACE 1  m FORWARD SCAN BACKWARD SCAN TEST AT SLAC

DOE Review June 2006 SLAC 13 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 14 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 Spacing 1.5 Radii Separation 1.2 Radii Separation

DOE Review June 2006 SLAC 15 STARTUP OF METROLOGY TEST LAB Polycold dual circuit, recirculating cryo-cooler (1.5 kW cooling -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 16 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  <<1  m 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 C Noise Limited To ~20 nm For Our Typical Displacements (~200  m) 25

DOE Review June 2006 SLAC 18 Cryostat Assembly Sequence – Designed For Tests & Arbitrary Removal Of Rafts For Repair/Replacement Silicon Carbide Grid Fast Actuators Cryo Plate Cool Plate Feedthrough Flange Outer Cylinder INSTALL GRID+ACTUATORS+CRYO PLATES INTO CLEAN & EMPTY BODY ADD RAFT DUMMY LOADS & TEST FAST ACTUATION SYSTEM ADD BLANKOFFS & TEST VACUUM & THERMAL SYSTEMS VERIFY CONTAMINATION SPECIFICATIONS

DOE Review June 2006 SLAC 19 RAFT LOADING SEQUENCE – IN ANY BAY WORKING UPSIDE DOWN IN CLEAN ROOM: REMOVE DUMMY LOAD IN BAY & INSTALL INSULATION ALIGN & SUPPORT RAFT FROM BACKSIDE WITH ROBOT INSTALL ONTO GRID’S KINEMATIC MOUNTS

DOE Review June 2006 SLAC 20 WARM METROLOGY PULL DOWN RAFT ONTO KINEMATIC MOUNTS ON GRID MAKE UP THERMAL CONNECTIONS TO CRYO PLATE # 1 VERIFY SURFACE FLATNESS – WARM – USING METROLOGY HEADS

DOE Review June 2006 SLAC 21 INSTALL BACK-END ELECTRONICS ATTACH BEE CARDS TO FLEX CABLE - TAKE UP SRVC LOOP MAKE UP THERMAL CONNECTIONS TO BEE CAGE ATTACH FO CABLE TO FEEDTHROUGH & TEST

DOE Review June 2006 SLAC 22 REPEAT FOR ALL BAYS REPEAT METROLOGICAL & FULL ELECTRONIC TESTING – COLD PROCEED TO INTEGRATE CRYOSTAT WITH CAMERA BODY CLOSE CRYOSTAT WITH L3 & REAR BULKHEAD VACUUM & THERMAL PROCESS THE CRYOSTAT – CHECK CONTAMINATION

DOE Review June 2006 SLAC 23 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 24 SPARE SLIDES

DOE Review June 2006 SLAC 25 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 26 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 1 G Sag of Loaded GRID

DOE Review June 2006 SLAC 27 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 28 PROTOTYPE LASER PROJECTOR HEAD THAT WOULD BE MOUNTED ON GRID CONSTRUCTED UTILIZING STABILIZED SINGLE MODE FIBER COUPLED DIODE LASER, DIFFRACTIVE & FOCUSSING ELEMENTS PROJECTOR HEAD DIODE LASER

DOE Review June 2006 SLAC 29 IMPROVEMENTS ADDRESSING REMAINING PROBLEMS ELONGATED ELLIPSES: INCREASE DENSITY TO BETTER UTILIZE GRID REAL ESTATE: ADD FOCUSSING ELEMENT AFTER DIFFRACTIVE ELEMENT ADD BEAM SPLITTER AFTER FOCUSSING ELEMENT OR DEVELOP CUSTOMIZED MICROMACHINED DIFFRACTIVE ELEMENTS

DOE Review June 2006 SLAC 30 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 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 31 CABLE TO BACK ANNULAR FLANGE ATTACH FIBER OPTIC & FLEX CABLES TO REAR FLANGE FT INSTALL OTHER ELEMENTS Guide, SH Sensors Temperature Monitoring & Control In-Situ Metrology, Fe55 Source, Service Cables… TEST CONNECTIONS

DOE Review June 2006 SLAC 32 Camera Integration and Test Sequence SENSOR ACCEPTANCE TEST Functional + Metrological (warm) RAFT ACCEPTANCE TEST Metrological (warm) RAFT TOWER ACCEPTANCE TEST Full 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 33 Camera Integration and Test Sequence CRYOSTAT BODY ACCEPTANCE TEST Vacuum Processing, Contamination, Plumbing, Thermal Controls, FPA Actuation FOCAL PLANE ASSEMBLY Metrological (warm), Limited Functional Testing of Sensors & Electronics Grid Cryo Plate Image Stabilization Actuators Outer Cylinder Tested Raft Towers BEE (not shown) Sensors Not Shown: Guide Shack Hartman Curvature Temp. Install L3 Window Or Blankoff Raft Towers Temp. install Cryostat Back Plate Back Flange

DOE Review June 2006 SLAC 34 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 Cables Elements of Thermal System Elements of Vacuum System In-Situ Metrology Systems X-Ray Source Calibration System Cryostat Body

DOE Review June 2006 SLAC 35 Camera Integration and Test Sequence CAMERA BODY & MECHANISMS ACCEPTANCE TESTS Mech.Functionality, Contamination CAMERA MECH. FUNCTIONALITY ACCEPTANCE 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 & Conditioning Exposure Control Elect. FP Control Elect. Vacuum /Purge Control Elect. Thermal Control Elect. Filter Changer Utilities Frame

DOE Review June 2006 SLAC 36 Camera Integration and Test Sequence CAMERA CALIBRATIONS AND FINAL ACCEPTANCE TEST L1/L2 Assembly Filters on Carousel Camera Calibrations See Talk: David Burke Filter in use LOAD FILTERS ADD L1/L2