1 / 59

Boulder

Boulder. SCUBA-2: The next generation submillimetre camera for the James Clerk Maxwell Telescope. 2. SCUBA-2. JAC Presentation Outline. 2. Scientific rationale Top Level Requirements SCUBA-2 Technology Detectors Cryogenics Optics The Project. Boulder.

rcaballero
Download Presentation

Boulder

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Boulder SCUBA-2: The next generation submillimetre camera for the James Clerk Maxwell Telescope 2 SCUBA-2

  2. JAC Presentation Outline 2 • Scientific rationale • Top Level Requirements • SCUBA-2 Technology • Detectors • Cryogenics • Optics • The Project

  3. Boulder SCUBA-2: The next generation submillimetre camera for the James Clerk Maxwell Telescope 2 Scientific Case

  4. IRAM- MPIfR 1.3mm array Current Bolometer Arrays in the Submillimetre Timeline: 1988 1996 1997 1998 JCMT-SCUBA 350/450 & 750/850mm JCMT-UKT14 350mm-2mm CSO-SHARC 350 mm array Retired in 1996 Number of pixels: 1 20 91/37 37 Sensitivity (Jy/Hz): 5-0.5 1 0.6/0.08 0.06

  5. Utilise the large field-of-view of JCMT to open-up new fields of study 2 Why do we need SCUBA-2? • New technologies  Larger format arrays • Increase scientific productivity of telescope • Maximise the returns with impending arrival of SMA link and heterodyne arrays • Keep the JCMT at the forefront of submm continuum astronomy

  6. Mapping speed >100 times that of SCUBA 2 Next generation : “SCUBA-2” • Per-pixel sensitivity Goal is for 50% better than SCUBA • Dual-wavelength imaging Operation at 450 and 850m • Image fidelity and map dynamic range Full-sampling of the image plane

  7. 2 LMT-BOLOCAM 1.1mm CSO-BOLOCAM 1.4mm Future Bolometer Arrays in the Submillimetre Timeline: 1999 Timeline: 1999 2001 2003 2004 2007+ JCMT-SCUBA 350/450 & 750/850mm SOFIA-HAWC 200mm FIRST- SPIRE 250, 350, 450mm SIRTF-MIPS 160mm CSO-SHARC-II 350/450 JCMT-SCUBA2 450/850mm SCUBA+ (JCMT) Bolocam (CSO) MIPS (SIRTF) HAWC (SOFIA) SHARC-II (CSO) Bolocam (LMT) SCUBA-2 (JCMT) SPIRE (FIRST) 91/37 pixels 400/65 mJy 40 160 384 600 151 3 144 40 384 560 512/1152/2048 ~40 22500/6500 210/50

  8. Field-of-view of current and future arrays Current Future Wavelength : 200 300 400 500 700 900 1200 2000 (microns)

  9. Large-scale extragalactic surveys • Plot source detection rate as a function of 5- depth • SCUBA-2 will detect ~20 sources per hour at optimum depth • SCUBA-2 has comparable mapping speed to a compact ALMA • Space-borne instruments become confusion noise limited • Dual wavelength capability of SCUBA-2 will give insights on dust spectra Simulation based on “modified Gaussian model” (Blain 1999)

  10. Debris disks - the state of the game... e.g. HST KECK JCMT/SCUBA Detected but too far away to image...

  11. 2 Debris dust disks SCUBA-2 impact: • Help answer one of the fundamental Origins questions: Are these the disks from which planets are made? • SCUBA-2 mapping speed:  30  faster to map to the same S/N • Improved map dynamic range: Should allow higher resolution imaging at 450m • Only a small sample studied so far… More than 20 other systems nearby that could be imaged...

  12. Unbiased Galactic Surveys 850m SCUBA ~10 arcmins SCUBA-2 450m SCUBA Survey of the Galactic Centre (Pierce-Price et al. in prep)

  13. Galactic Centre Full moon SCUBA Galactic Centre Survey M8 ~ 10 shifts (or 80 hrs) of telescope time M16 SCUBA-2 Galactic PLANE Survey?

  14. 2 Unbiased Galactic Surveys • Scientific goals: Complete census of giant molecular clouds, star- forming regions, protostars, pre-stellar cores etc. • Mapping speed improvement: ~300 times faster to map to the same S/N Entire clouds can be mapped in only a few hours... • Increased sensitivity and map dynamic range: Source counts and the initial mass function Spectral index maps from dual-wavelength imaging • SCUBA-2 Galactic Plane survey would become a reality...

  15. Large-scale surveys and galaxy clustering • Shows positions of luminous dusty starburst galaxies tracing the large-scale structure at early epochs • Large sample sizes (~5000) can test theories of structure formation • SCUBA-2 can carry out large, sensitive and unbiased surveys in modest amounts of time ~ 1 arcmin CDM simulation at z ~ 3 (Governato et al. Nature 1999)

  16. 2 Large-scale extragalactic surveys • Scientific goals: Unbiased surveys of different sizes and depths for studying the formation of massive galaxies • Mapping speed improvement: Source count detection increases by > 100 times Large samples spanning ranges of flux and redshift • Increased sensitivity: Point-sources can be measured much more quickly • Dual wavelength imaging/photometry: Provide unique insights on dust spectra

  17. 2 Polarimetry with SCUBA-2 • Example: OMC3 molecular cloud - a highly ordered field crossing the filament • Science impact: Generally recognised that magnetic fields play an important role in star formation • Data consists of ~400 vectors which needed 5 shifts of SCUBA/JCMT time • Main SCUBA limitation: Undersampled field leads to systematic errors in polarisation images • Large field-of-view: Large-scale fields to be mapped very quickly OMC3 (Matthews & Wilson in press) • Improved sensitivity: Lower polarised flux limits to study magnetic fields in pre- stellar cores and nearby galaxies e.g. M51 could be mapped to p  0.5% in ~10hrs

  18. 2 Summary • SCUBA-2 mapping speed >100 times faster than SCUBA • For point-source work there is a significant speed advantage • Image fidelity will improve as a result of the instantaneously fully-sampled image plane • Many science areas that will benefit from this unique facility instrument

  19. Boulder SCUBA-2: The next generation submillimetre camera for the James Clerk Maxwell Telescope 2 Top Level Requirements

  20. 2 Summary of main requirements • A fully-sampled image plane covering at least 8 arcmin-square • Per-pixel sensitivity of < 65 and 320mJy/Hz at 850 and 450m • Simultaneous operation at two wavelengths • A compact design allowing easy maintenance and support • Novel observing modes to improve image fidelity and map dynamic range

  21. SCUBA-2 Field-of-view Array boundary Vignetted area ~11arcmin ~8 arcmin 64 arcmin2 95 arcmin2 (B) Minimum F-O-V (A) Maximum F-O-V

  22. 2 2 Pixel Details • An 8  8 arcmin field, fully-sampling the image plane:  6,500 pixels at 850m and 22,500 at 450m • Increase in mapping speed >> 100 at both wavelengths • Physical dimensions of array: • For final optics of f/2.5 the arrays are ~120mm in diameter

  23. Expected performance

  24. 2 Summary of main systemcomponents • Detectors: Transition-edge sensors with SQUID readouts • Electronics: Multiplexed SQUIDs and room temperature amplifiers • Cryogenics: Two compact 3He systems and two pulse- tube coolers • Cold optics: Re-imaging mirrors and array baffling; magnetic shielding for SQUIDs • Relay mirrors: To re-image beam onto Nasmyth platform • Data acquisition:VME crate (or similar) to fast workstation

  25. 2 Observing Modes • Calibration: Skydip and skycal • Flatfield: Use the sky to determine the flatfield • Stare-map: Simple point-and-shoot - similar to a CCD or IR array • Scan-map: Fast scanning, drift scanning or dithering method

  26. Some practical examples...

  27. Example: Deep Extragalactic Surveys SCUBA CFRS Survey 7 × 6.2 arcmin 22 sources > 3 rms noise ~ 1 mJy 78 hrs of Band 1/2 time SCUBA CFRS Survey (7 × 6.2 arcmin) 22 sources > 3 rms noise ~ 1.0 mJy 78 hrs of Band 1/2 time SCUBA-2 Survey in the same time to 1mJy rms ~ 2 degree2 ~ 1250 sources > 3

  28. SCUBA-2: The next generation submillimetre camera for the James Clerk Maxwell Telescope 2 Bolometer Technology

  29. 2 Voltage-Biased Superconducting Transition-Edge Thermometers 0.06 I SQUID Amplifier 0.04 Resistance (ž) Vbias 0.02 R(T) TES µcal 0 95.8 96 96.2 Temperature (mK) • Joule power causes each pixel to self-regulate in temperature: Self-biasing allows large format arrays

  30. 2 P joule V2 Pres P R res Negative Electrothermal Feedback As the film cools, R0, and Pjoule increases. I SQUID V Stable equilibrium 2 V R TES Thermal conductance Temperature Self-Regulation Heat Reservoir

  31. 2 Normal metal Superconductor Substrate Superconductor / Normal Metal BilayerTransition-Edge Sensor Superconductors in use: Aluminum Tc ~ 1.1 K Molybdenum Tc ~ 0.92 K Titanium Tc ~ 0.4 k Iridium Tc ~ 0.14 K • A bilayer of a thin superconducting film and a thin normal metal acts as a single superconductor with a tunable - the “proximity effect” • Sharp • Reproducible  ~2 mK • Tunable

  32. 2 Feedback Flux SQUID Output Voltage Input Coil SQUID Bias Current X X LIN X X LFB SQUIDs Column Flux Bias Column Output Addr. 1 LIN LFB X X Addr. 2 LFB LIN X X Addr. 3 Addr. N LIN LFB Addr. N+1 Price of TDM with SQUIDs: must use smart digital feedback which remembers last feedback setting to zero flux

  33. 2 X X X X X SQUIDs Must use series-array SQUID (invented at NIST) to couple to room-temperature amplifiers. • Required for high bandwidth and high dynamic range for switching feedback operation. • Conventional SQUIDs: impedance is too low. • Alternative high-bandwidth SQUIDs (“Additional positive feedback”, and other techniques to steepen V- curve): dynamic range is too small. Voltage Bias X LNYQ RLOAD X LSA X LIN LFB X X RTES X X LNYQ LIN RTES X X LFB LNYQ LIN RTES LFB X X

  34. 2 SQUID Multiplexors Column 2 Column 1 RADD RADD LIN LIN X X X X LFB LFB Row 1 RADD RADD LIN LIN X X X X LFB LFB Row 2 RADD RADD RADD RADD LIN LIN X X X X LFB LFB Row N RADD RADD

  35. 2 SQUID Multiplexer Chip 1  8 SQUID multiplexer (one column)

  36. 2 0.08 0.06 0.04 0.02 0 -0.02 0 0.5 1 1.5 2 MUX Prototype Operational De-Multiplexed Multiplexed SQUID output (mV) Time (ms) Extendable to 200  200 arrays with 200 readout channels and 201 address lines

  37. 2 Electronics Digital Integrator Computer ADC FPGA Fiber Optic DSP DAC Digital Integrator Board Interface Board Soon to be interfaced to the address line driver board for multiplexing

  38. 2 Digital Feedback Board

  39. Practical example: Photon counting

  40. Mechanical/thermal/electrical link Metal absorber 5mm TES Si grid l/4 cavity Reflector Silicon substrate Reflector Silicon grid l/4 cavity 0.3 K 50 mm • Silicon grids with resonant absorbers 400 mm TES 0.3 K Absorbing grid Reflector Indium bumps FIRST-SPIRE: CEA-SACLAY/LETI MICROMACHINED ARRAY OPTION, ADOPTED FOR TES USE Absorbing metal film

  41. 2 Summary of advantages: TES with voltage bias and electrothermal feedback • large  = 1/R dR/dT - many hundreds per K • effective time constant decreased • self biasing - excellent for arrays • Johnson noise suppressed out to eff • thermodynamic limit to energy resolution improved by electrothermal feedback by a factor of (3/) • performance limited only by phonon fluctuations • linear and measures absorbed power

  42. 2 Summary of advantages (continued): TES with voltage bias and electrothermal feedback • separate control of absorption and detection functions • easy control of TES by photolithography and pixel/array structure using Si micromachining • multiplex capability to at least 300  300 • photon counting into the mid-infrared • high count rates (10’s of kHz) • low impedance - not microphonic!

  43. 2 TES with voltage bias and electrothermal feedback Summary of disadvantages: • Must be cooled below 1 K • SQUIDS need shielding from magnetic fields • But cryo-free 3He systems and ADRs now available

  44. SCUBA-2: The next generation submillimetre camera for the James Clerk Maxwell Telescope 2 Optical design

  45. SCUBA-2: The next generation submillimetre camera for the James Clerk Maxwell Telescope 2 Cryogenics

  46. Cryogenics 2 Overall Cryogenics Requirements: • cryofree • 3He temperatures for 2 arrays • 4K for optics • low vibration • location on the LH Nasmyth • stay cold for >> 6 months • low maintenance

  47. 4K system(s): cryofree - use closed-cycle coolers Low vibration - Pulsed tubes? Temperature stability <0.2 K rms? Low maintenance 60K for second stage unbaffled window load is 8.4 watts superinsulation load ~ 25 watts 2 Cryogenics

  48. 2 Cryogenics He3 system(s): • Cool arrays structures to ~ 250 mK for ~ 20 hours • Temperature stability ~ few K • Cope with heat loads from ~ 2000 wires • Cycle time < 2 hours • Plug and play system • Quote from Chase for “Helium-10” fridge

  49. 2 Cryogenics He3 stage Pumping tube Cryopump Detector system - imagine this not here to have an idea of the naked system Base plate - the only point of mechanical attachment to thecryostat Edge of secondcryopump

  50. 2 Cryogenics Cryostat: • support the optical systems • support a good vacuum for long term hold time and low contamination of arrays • proper routing of wiring through the cryostat • easy access to internal components for maintenance • mechanical/electronic/electrical/safety interfaces to telescope

More Related