Boulder SCUBA-2: Next-Gen Submillimetre Camera for JCMT

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