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LSST Camera Cryostat Design & Integration

LSST Camera Cryostat Design & Integration. DOE Program Review SLAC June 2006 Rafe H. Schindler Experimental Group E - SLAC. Overview. SLAC Is Responsible for The Major Mechanical Components & The Final Integration & Testing of the LSST Camera:

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LSST Camera Cryostat Design & Integration

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  1. LSST Camera Cryostat Design & Integration DOE Program Review SLAC June 2006 Rafe H. Schindler Experimental Group E - 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 One of the More Challenging Engineering Tasks REQUIREMENTS COMBINE: • Mounting of Close-Packed Rafts & Ancillary Sensors Onto GRID --Maintaining Overall Flatness (~10 um) • Rapid Sub-mm 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 DOE Review June 2006 SLAC

  4. Focal Plane Flatness Budget Sensor Module 5mm p-v flatness over entire sensor surface Before FPA I&T Raft Assembly 6.5mm p-v flatness over entire surfaces of sensors Focal Plane Assembly 10mm p-v flatness over entire surfaces of sensors (at -100 0C & All Camera Orientations) 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 mm Gravity Sagand<0.2mm Sagitta for DT~10C • Make RAFTS Interchangeable Without Further Adjustment • Use 3-Vee kinematic coupling with sub-mm 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 and GRID Metrology Strategy To Speed Assembly Raft Metrology Fixture Embodies Desired Geometry Needed on Grid Raft Metrology Fixture FEE Cage AT BNL Raft Flat and parallel to 3 balls ~100 nm Set up detectors coincident to the flat surface of the fixture DOE Review June 2006 SLAC

  7. Cold Plate Cold Plate FEE Cage GRID GRID Raft Kinematic Mounting Points On The GRID Are Measured & Adjusted to Mimic Raft Metrology FixtureDuring Assembly of Focal Plane, a Motion Stage Lifts Raft Onto GRID Kin. Mounting Points From BehindThermal Connections Are MadeMetrological Verification Follows Immediately (see following slides) 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 ~12cm ADJUSTORS FOR EACH SENSOR’S KIN. MNT. TO AlN RAFT BASE 3-Vee BLOCKS ON RAFT To Mount RAFT to GRID SPRING TO LOAD KINEMATIC MOUNT TO GRID 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 <<0.5mm 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 DOE Review June 2006 SLAC

  10. Non-Contact Laser Displacement Heads For Metrology During Assembly 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-mm Metrology Can Be Done Rapidly By Stitching Smaller Overlapping Areas OPTICAL REF. FLAT LASER TRIANGULATION HEAD XY STAGE TRIANGULATION HEAD FOCAL PLANE L3 or WINDOW SHOWN UPSIDE DOWN

  11. Test of Non-Contact Displacement Heads SiC Sample 12cm Sensor Head (LK-G37) Dual Controller XY Actuation Stage Optical Flat (reference) Sensor Head (LK-G15) DOE Review June 2006 SLAC

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

  13. 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 Bottom View Shows Partial Population of Focal Plane Array Camera Focal Plane GRID Dual sensor XY carriage Displacement sensors (up & down looking) Inspection Opt. Table Assy Opt. Table Reference surface XY carriage 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) 3mm Spacing 1.2 Radii Separation 10mm Spacing 1.5 Radii Separation Input Error • Propagated Error Distributions Compared to Input errors. Four Simulations (2x Different Grid Spacings and 2x Ref. Separations) Sample 65cm Diam. Focal Plane With a 20cm Flat DOE Review June 2006 SLAC

  15. STARTUP OF METROLOGY TEST LAB RGA TEST CHAMBER TURBO PUMP XY STAGE OPTICAL WINDOW TEMP. & PRESS. CNTRLS 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) DOE Review June 2006 SLAC

  16. In-Situ Metrology: Diffraction Pattern Generator • Measure FPA Flatness Directlyby Centroiding …Ellipses & Measuring Deviations of Known Pattern • Centroiding Digital Images off Silicon Gives a s <<1mm on CCD Piston Laser & Grating CCD Imaged Ellipse Silicon Wafer • Goal: Shorter spots, increased density & uniform intensity Raft GrantAwardedat Stanford Nanofabrication Facility To Pursue Grating Fabrication Techniques DOE Review June 2006 SLAC

  17. 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 (~200mm) 25

  18. Cryostat Assembly Sequence – Designed For Tests & Arbitrary Removal Of Rafts For Repair/Replacement Outer Cylinder Fast Actuators SiliconCarbideGrid Cryo Plate Cool Plate Feedthrough Flange 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. REPEATFOR ALL BAYS CLOSE CRYOSTAT WITH L3 & REAR BULKHEAD VACUUM & THERMAL PROCESS THE CRYOSTAT – CHECK CONTAMINATION REPEAT METROLOGICAL & FULL ELECTRONIC TESTING – COLD PROCEED TO INTEGRATE CRYOSTAT WITH CAMERA BODY 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. Metrology of FPA Under Vacuum and Cold Cryostat Closed With Vacuum Window or L3 and Cooled To Operating Temp. Metrology Repeated [Applying Small Optical Corrections] Rear Bulkhead Closed Displacement Sensor Measures FPA Through Vacuum Barrier Window. Cryostat Body Dual sensor XY carriage Displacement sensors (up & down looking) Inspection Opt. Table Assy Opt. Table Reference surface XY carriage DOE Review June 2006 SLAC

  26. Simplify Metrology By Use of Silicon Carbide • Significantly Better Structural and Thermal Properties Than Metals • Expect ~ 1/3 mm Sag Under Gravity & < 0.5 mm From Thermal Distortion • Good CTE Match To Al Ni In Rafts Support Support 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 DIODE LASER PROJECTOR HEAD DOE Review June 2006 SLAC

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

  30. OPTIMIZED MICROMACHINED 2D ARRAY OF APERTURES Laser generates array of spots with relatively uniform amplitudes if apertures ~l Pattern from 0.5 micron diameter circular apertures on a grid of 150 columns per mm and 50 rows per mm. Layout for chrome-on-glass diffraction grating with electron beam etched apertures being produced at Stanford in June 2006 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 Si CCD Sensor Raft Assembly CCD Carrier Thermal Strap(s) SENSOR ACCEPTANCE TEST Functional + Metrological (warm) Flex Cable & Thermal Strap(s) Sensor Packages FEE Cage FEE Raft Structure RAFT TOWER ACCEPTANCE TEST Full Functional + Thermal + Metrological (warm and cold) + Contamination(?) RAFT ACCEPTANCE TEST Metrological (warm) DOE Review June 2006 SLAC

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

  34. Camera Integration and Test Sequence Cryostat Rear Bulkhead Cryostat Body Focal Plane (one raft shown) L3 and/or Window • 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 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 DOE Review June 2006 SLAC

  35. Camera Integration and Test Sequence Base Plate Utilities Frame Filter Carousel, with Dummy Filters • Electrical Integration Camera Housing • Plumbing Integration • -thermal system • -vacuum system • -purge system Shutter (temp. install) Filter Changer, (temp. install) Shutter CAMERA BODY & MECHANISMS ACCEPTANCE TESTS Mech.Functionality, Contamination Filter Changer Functional Tests Power & Conditioning Exposure Control Elect. FP Control Elect. Vacuum /Purge Control Elect. Thermal Control Elect. CAMERA MECH. FUNCTIONALITY ACCEPTANCE TEST Cryostat Assembly With L3 DOE Review June 2006 SLAC

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

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