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LSST Camera Overview

LSST Camera Overview. SLAC Program Review June 7, 2006 Kirk Gilmore Stanford/SLAC/KIPAC. Camera Assembly. Raft Tower. L3 Lens. Shutter. L1/L2 Housing. Filter in stored location. L1 Lens. Camera Housing. L2 Lens. Filter in light path. Telescope/Camera Configuration.

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LSST Camera Overview

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  1. LSST Camera Overview SLAC Program Review June 7, 2006 Kirk Gilmore Stanford/SLAC/KIPAC

  2. Camera Assembly Raft Tower L3 Lens Shutter L1/L2 Housing Filter in stored location L1 Lens Camera Housing L2 Lens SLAC Program Review June 7, 2006 Filter in light path

  3. Telescope/Camera Configuration SLAC Program Review June 7, 2006

  4. Flowdown from Science to Camera Four Main Science Themes for LSST: 1. Constraining Dark Energy and Dark Matter 2. Taking an Inventory of the Solar System 3. Exploring the Transient Optical Sky 4. Mapping the Milky Way MajorImplications to the Camera: • Large Etendue • Excellent Image Quality and Control of PSF Systematics • High Quantum Efficiency over the Range 320 – 1,050 nm • Fast Readout SLAC Program Review June 7, 2006

  5. Large Etendue

  6. Excellent Image Quality with ~10 micron (0.2 arc-sec ) diameter images Camera: Flat 64 cm f CCD array Aspheric surface

  7. SDSS Band-pass Transition Half Maximum Transmission Wavelength (nm) g r i z Blue side 402 552 693 840 Red side 548 693 851 - Photometric redshifts of galaxies Separation of stellar populations Photometric selection of quasars LSST Band-pass Transition Half Maximum Transmission Wavelength (nm) u g r i z Y Blue side 350 400 552 691 818 948 Red side 400 552 691 818 922 1050 G-Balmer break @400. OI line@ 557 R-matches SDSS I-red side short of sky emission @826 Z-red side stop before H2O bands Y– red side cut-off by sensor

  8. LSSTSystem Throughput

  9. Optics Summary • Baseline design of LSST camera optics exists • Refinements continuing • Optics fabrication discussed with vendors • Substantial industrial base exists for optics fabrication • Optics coating discussed with vendors • Adequate industrial base exists for optics coating Next steps • Complete tolerance analysis for camera optics • Complete RFQ for filter coating risk reduction study SLAC Program Review June 7, 2006

  10. Sensor Requirements • High QE to 1000nm  thick silicon (> 75 µm) • PSF << 0.7” (0.2”)  high internal field in the sensor  high resistivity substrate (> 5 kohm∙cm)  high applied voltages (30 - 50 V) • Fast f/1.2 focal ratio  sensor flatness < 5µm  package with piston, tip, tilt adj. to ~1µm • Wide FOV  ~ 3200 cm2 focal plane  > 200-CCD mosaic (~16 cm2 each)  industrialized production process required • High throughput  > 90% fill factor  4-side buttable package, sub-mm gaps • Fast readout (1 - 2 s)  segmented sensors (~6400 TOTALoutput ports) SLAC Program Review June 7, 2006

  11. Detail of output port Full CCD showing segmentation. Note pads on left and right edges only Detail of one edge Multi-port 4K x 4K = 16M Pixel CCD strawman 32 segments/port J. Geary, “LSST Strawman CCD Design”, Dec. 2004

  12. Control of PSF Monte-Carlo simulation of long-wavelength light absorption silicon sensorRight-hand figures show the simulated points where 10,000 photons are absorbed. Left-hand panels show the projections onto the charge-collection plane.

  13. Focal Plane Metrology Requirement Sensor Module 5mm p-v flatness over entire sensor surface Raft Assembly 6.5mm p-v flatness over entire surfaces of sensors Focal Plane Assembly 10mm p-v flatness over entire surfaces of sensors SLAC Program Review June 7, 2006

  14. Sensor Study Projects • Funding mass-production vendor for design study plus fabrication of known-good CCDs on 100u high-rho silicon. • Our first tests of thick CCDs with backside bias voltage. • Verify QE, PSF, dark current performance. _______________________________________________________________ • Funding the development of a CMOS readout 4K X 4K, 10u pixel array with 100u thick high-rho material and backside bias capability. Very promising but largely untested for precision astronomical photometry. • Pros: electronic shutter, very low power, low blooming, interface ASIC. Cons: noise floor for single reads, crosstalk between channels. SLAC Program Review June 7, 2006

  15. Focal Plane Read-out: The Challenge • Large focal plane  201 Sensors, 3.2 Gpixels • High speed readout  2 sec goal • Low read noise, sky noise dominated > ~ 5 e rms • High crosstalk immunity ~ 80 db • Fully synchronous readout across entire focal plane • Large number of sensor pads (signals)  150/sensor ~ 30,000 pads total • High vacuum environment  contamination control • Minimization of vacuum feedthroughs SLAC Program Review June 7, 2006

  16. Focal Plane Read-out: Strategy • Utilize highly segmented sensors to allow modest read speed • 32 segments (ports) / sensor  250 kHz readout • “Raft” based electronics package  9 x 32 = 288 ports per raft • Electronic package located within Dewar to avoid ~30k Dewar penetrations • FPA electronics packaging requirement All electronics must live in “shadow” of raft footprint ~ 125 mm x 125 mm • 21 rafts 6,048 readout ports (source followers) • Data output on one optical fiber per raft  144 Mpixels/2 sec ~1.4 Gbps on fiber SLAC Program Review June 7, 2006

  17. Raft Towers Si CCD Sensor Raft Assembly CCD Carrier Thermal Strap(s) SENSOR Flex Cable & Thermal Straps Sensor Packages FEE Cage FEE Raft Structure RAFT TOWER RAFT SLAC Program Review June 7, 2006

  18. In-dewar electronics partitioning 32-port CCD 32-port CCD 32-port CCD RIGHT LEFT • Front End Boards (6 per raft): • 48-channel video signal chain through CDS processing • clock and bias drive • ASIC-based 180K Flex cables (~ 20,000 signals) Cold sink 240K • BEE motherboard and backplane: • differential receiver • signal chain ADC • frame buffer • data transport to optical fiber • clock pattern generation • clock and bias DACs SLAC Program Review June 7, 2006

  19. Camera Overview Tasks and Summary • Detector requirements: (Radeka/Geary - BNL/SAO) • 10 mm pixel size Pixel full-well > 90,000 e– High QE 400 – 1000 nm • Low noise (< 5 e– rms), fast (< 2 sec) readout, stable T (-90 C) • Package large number of detectors, with integrated readout electronics, • with high fill factor and serviceable design (O’Connor/Oliver - BNL/Harvard) • Sensor and focal plane precision alignment/stabilility/motion control Sensor flatness 5u p-v, focal plane flatness 10u p-v(Takacs/Rasmussen/Schindler - BNL/SLAC/SLAC) • Fabricate large diameter (75cm) filters with uniform coatings (Olivier - LLNL) • Constrained volume (camera in beam) (Nordby - SLAC) • Makes shutter, filter exchange mechanisms challenging • Focal Plane Calibration - (Burke - SLAC) SLAC Program Review June 7, 2006

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