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Boulder

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

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Boulder

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

  2. 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 • A high level of user support

  3. 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

  4. 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: • Pixel size >  to ensure good coupling • For final optics of f/2.5 the arrays are ~120mm in diameter

  5. Expected performance

  6. 2 Wavelengths of operation • Propose to operate a two fixed wavelengths • No equivalent of the SCUBA filter drum • Provision for changing filters if needed: e.g. 450m  350m • This will require a hardware change

  7. 2 Optical design • Complex design since need to re-image a large field-of-view onto a small array • Necessitates that SCUBA-2 be located on the Nasmyth platform • All mirror design with complex path • Mirrors will be large and aspheric in shape • expensive to manufacture...

  8. 2 Summary of main systemcomponents • Detectors: Transition-edge sensors with SQUID readouts • Electronics: Multiplexed SQUIDs and room temperature amplifiers • Filters: Fixed frequency operation at 450 and 850m • 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

  9. 2 Observing Modes • Calibration: Skydip and sky-cal • 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

  10. Some practical examples...

  11. 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

  12. 2 Summary: SCUBA-2 Goals • Field-of-view : At least 8 arcmin-square • Sensitivity : Sky background limited • Wavelengths : 450 and 850m • Mapping speed : >100 times that of SCUBA • Confusion limit : Achievable in about 2 hours • Cryogenics : Cryo-free (closed cycle systems) • On the telescope : In 5 years time!

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