SCUBA-2 is a revolutionary 10,000 pixel wide-field submillimetre camera, recently commissioned and now operational
at the James Clerk Maxwell Telescope (JCMT). Twin focal planes each consist of four 32 by 40 sub-arrays of
superconducting Transition Edge Sensor (TES) bolometers, the largest combined low temperature bolometer arrays in
operation, to provide simultaneous imaging at wavelengths of 450 and 850 microns. SCUBA-2 was designed to map
large areas of sky more than 100 times faster than the original ground breaking SCUBA instrument and has achieved this
goal. In this paper we describe the performance of the instrument and present results of characterising the eight science
grade TES bolometer arrays. We discuss the steps taken to optimise the setup of the TES arrays to maximise mapping
speed and show how critical changes to the sub-array module thermal design, the introduction of independent focal plane
and 1K temperature control and enhancements to the cryogenics have combined to significantly improve the overall
performance of the instrument.
We describe the current state of the ground segment of Herschel-SPIRE photometer data processing, approximately
one year into the mission. The SPIRE photometer operates in two modes: scan mapping and chopped
point source photometry. For each mode, the basic analysis pipeline - which follows in reverse the effects from
the incidence of light on the telescope to the storage of samples from the detector electronics - is essentially
the same as described pre-launch. However, the calibration parameters and detailed numerical algorithms have
advanced due to the availability of commissioning and early science observations, resulting in reliable pipelines
which produce accurate and sensitive photometry and maps at 250, 350, and 500 μm with minimal residual
artifacts. We discuss some detailed aspects of the pipelines on the topics of: detection of cosmic ray glitches,
linearization of detector response, correction for focal plane temperature drift, subtraction of detector baselines
(offsets), absolute calibration, and basic map making. Several of these topics are still under study with the
promise of future enhancements to the pipelines.
SCUBA-2 is a state of the art 10,000 pixel submillimeter camera installed and being commissioned at the James Clerk
Maxwell Telescope (JCMT) providing wide-field simultaneous imaging at wavelengths of 450 and 850 microns. At each
wavelength there are four 32 by 40 sub-arrays of superconducting Transition Edge Sensor (TES) bolometers, each
packaged with inline SQUID multiplexed readout and amplifier. In this paper we present the results of characterising
individual 1280 bolometer science grade sub-arrays, both in a dedicated 50mk dilution refrigerator test facility and in the
instrument installed at the JCMT.
SCUBA-2 is a new wide-field submillimeter continuum instrument being commissioned on the James Clerk
Maxwell Telescope on Mauna Kea in Hawaii. SCUBA-2 uses large-scale arrays of superconducting bolometers
with SQUID- (superconducting quantum interference device) based multiplexing and amplification. The sensitivity
of the devices that compose the detector arrays to magnetic fields is such that magnetic shielding, consisting
of superconducting and high-permeability materials, was fitted to the detector enclosure at 1 K to reduce the
magnetic field strength at the focal plane. This paper describes the design and construction of the cryogenic
shielding, and presents verification measurements. The shielding performance was found to meet the instrument
requirements, and compared well to the modelled results.
SCUBA-2 is a new wide-field submillimeter continuum instrument being commissioned on the James Clerk
Maxwell Telescope on Mauna Kea in Hawaii. SCUBA-2 images simultaneously at 450 and 850 μm using large-scale
arrays of superconducting bolometers, with over five thousand pixels at each wavelength. The arrays are
cooled to less than 100 mK by the mixing chamber of a dilution refrigerator (DR), with a radiation shield at a
nominal temperature of 1 K cooled by the DR still. The DR is a "dry" system, using a pulse tube cooler for
precooling of the circulating helium in place of a liquid helium bath. This paper presents key performance data
for the DR.
Bolometers are very simple devices. In principle, the behaviour of a bolometer can be described by a simple model along
with a small number of parameters. The SPIRE instrument for the Herschel Space Observatory contains five arrays of
NTD germanium spiderweb bolometers containing up to 139 pixels. We show from characterisation measurements on the
ground using the flight read-out system that the bolometers follow the ideal model extremely well, are very stable, and that
the read-out system is sufficiently well behaved to take advantage of this. Calibration should be greatly simplified by being
able to take advantage of this behaviour.
SPIRE, the Spectral and Photometric Imaging Receiver, is a submillimetre camera and spectrometer for Herschel. It
comprises a three-band camera operating at 250, 350 and 500 µm, and an imaging Fourier Transform Spectrometer
covering 194-672 μm. The photometer field of view is 4x8 arcmin., viewed simultaneously in the three bands. The FTS
has an approximately circular field of view of 2.6 arcmin. diameter and spectral resolution adjustable between 0.04 and 2
cm-1 ( λ/▵λ=20-1000 at 250 μm). Following successful testing in a dedicated facility designed to simulate the in-flight
operational conditions, SPIRE has been integrated in the Herschel spacecraft and is now undergoing system-level testing
prior to launch. The main design features of SPIRE are reviewed, the key results of instrument testing are outlined, and
a summary of the predicted in-flight performance is given.
Various planned space astronomy missions such as SPICA, SAFIR, Constellation-X and XEUS will require detectors
operating at ultra-low temperatures. Our current relevant experience in space is limited, and future instruments are in any
case likely to have more demanding requirements. We must therefore take advantage of experience on the ground. The
SCUBA-2 ground-based instrument is probably the largest and (thermally) most complex astronomical instrument ever
built to operate at such low temperatures. The thermal design has been very successful, and I discuss techniques we have
developed and lessons we have learned that will be applicable to future space missions.
We present the results of characterization measurements on a 1280 pixel superconducting bolometer array designed for operation at wavelengths around 450 μm. The array is a prototype for the sub-arrays which will form the focal plane for the SCUBA-2 sub-mm camera, being built for the James Clerk Maxwell Telescope (JCMT) in Hawaii. With over 10 000 pixels in total, it will provide a huge improvement in both sensitivity and mapping speed over existing instruments. The array consists of molybdenum-copper bi-layer TES (transition edge sensor) pixels, bonded to a multiplexer. The detectors operate at a
temperature of approximately 175 mK, and require a heat sink at a temperature of approximately 60 mK. In contrast to previous TES arrays, the multiplexing elements are located beneath each pixel (an "in-focal plane" configuration). We present the results of electrical and optical measurements, and show that the optical NEP (noise equivalent power) is less than 1.4 × 10-16 W Hz-0.5 and thus within the goal of 1.5 × 10-16 W Hz-0.5.
SCUBA-2 is an innovative 10,000 pixel submillimeter camera due to be delivered to the James Clerk Maxwell Telescope in late 2006. The camera is expected to revolutionize submillimeter astronomy in terms of the ability to carry out wide-field surveys to unprecedented depths addressing key questions relating to the origins of galaxies, stars and planets. This paper presents an update on the project with particular emphasis on the laboratory commissioning of the instrument. The assembly and integration will be described as well as the measured thermal performance of the instrument. A summary of the performance results will be presented from the TES bolometer arrays, which come complete with in-focal plane SQUID amplifiers and multiplexed readouts, and are cooled to 100mK by a liquid cryogen-free dilution refrigerator. Considerable emphasis has also been placed on the operating modes of the instrument and the "common-user" aspect of the user interface and data reduction pipeline. These areas will also be described in the paper.
The Spectral and Photometric Imaging REceiver (SPIRE) is one of the three scientific instruments to fly on the
European Space Agency's Herschel Space Observatory, and contains a three-band imaging submillimetre photometer
and an imaging Fourier transform spectrometer. The flight model of the SPIRE cold focal plane unit has been built up
in stages with a cold test campaign associated with each stage. The first campaign focusing on the spectrometer took
place in early 2005 and the second campaign focusing on the photometer was in Autumn 2005. SPIRE is currently
undergoing its third cold test campaign following cryogenic vibration testing. Test results to date show that the
instrument is performing very well and in general meets not only its requirements but also most of its performance
goals. We present an overview of the instrument tests performed to date, and the preliminary results.
The Spectral and Photometric Imaging REceiver (SPIRE) is one of the three scientific instruments on the European Space Agency's Herschel mission. At the start of 2004 the Cryogenic Qualification Model (CQM) of SPIRE was tested with the aim of verifying the instrument system design and evaluating key performance parameters. We present a description of the test facility, an overview of the instrument tests carried out on the CQM, and the first results from the analysis of the test data. Instrument optical efficiency and detector noise levels are close to the values expected from unit-level tests, and the SPIRE instrument system works well, with no degradation in performance from stray light, electromagnetic interference or microphonically induced noise. Some anomalies and imperfections in the instrument performance, test set-up, and test procedures have been identified and will be addressed in the next test campaign.
SPIRE, the Spectral and Photometric Imaging Receiver, is one of three instruments to be flown on ESA's Herschel Space Observatory. It contains a three-band submillimetre camera and an imaging Fourier transform spectrometer, and uses arrays of feedhorn-coupled bolometric detectors operating at a temperature of 300 mK. Detailed software simulators are being developed for the SPIRE photometer and spectrometer. The photometer simulator is based on an adaptable modular representation of the relevant instrument and telescope subsystems, and is designed to produce highly realistic science and housekeeping data timelines. It will be used for a variety of purposes, including instrument characterisation during ground testing and in orbit, testing and optimisation of operating modes and strategies, evaluation of data reduction software using simulated data streams (derived by "observing" a simulated sky intensity distribution with the simulator), observing time estimation, and diagnostics of instrument systematics. In this paper we present the current status of the photometer simulator and the future development and implementation strategy.
The SCUBA-2 instrument is a new wide field submillimeter imager currently being designed for the James Clerk Maxwell telescope on Mauna Kea in Hawaii. The instrument will observe simultaneously in the 450 and 850 micron bands and has a field of view of approximately 50 square arcminutes. To meet the performance requirements the detectors require a heat sink at a temperature of 50 mK or lower, and must be surrounded by an enclosure at a temperature of 1.1 K or below.
Cooling is provided by the mixing chamber and still of a cryogen-free dilution refrigerator (DR), via thermal links of the order of a metre in length. A challenging set of requirements result from the need for a small temperature drop between the detectors and the refrigerator insert despite the large distance between them, the need to provide flexibility in the links to allow for movement during thermal contraction, and the need to allow for the detectors to be
removed from the cryostat. Further, the arrays require a mounting structure which provides rigid mechanical support from the 1-K stage yet causes a very small heat input to millikelvin stage. This paper describes the design which has been evolved to meet these difficult (and often conflicting) requirements.
The Astronomical Instrumentation Group at University of Cardiff is
already a UK center for submillimetre bolometric detector testing.
The next generation of submillimetre astronomical instrumentation
will incorporate arrays of transition-edge sensor (TES)
bolometers. With the recently expanded facilities and personnel,
the University of Cardiff is poised to become a UK centre for TES
development and testing. We have undertaken a coordinated
programme to develop TES simulation and test capabilities. One
aspect of the programme is to address the problem of saturation of
TES bolometers at high optical loads. We have developed a
"tunable-G" device, which can vary its thermal conductance
whilst in operation. For infrastructure, several sub-Kelvin
cryogenic testbeds have been specifically designed to suit the
requirements of testing submillimetre TES development bolometers.
A description of our tunable-G device to solve the optical
saturation problem will be given along with a description of the
test facilities available at Cardiff.
The SCUBA-2 instrument is a new wide-field imager under development for the James Clerk Maxwell Telescope on Mauna Kea in Hawaii and due to be operational in 2006. The instrument has two separate focal planes and is designed to observe simultaneously at wavelengths of 450 and 850μm. The instrument cryostat will weigh around 2500kg and has a volume of approximately 2.4x1.8x2.0m. The two detector arrays are operated at ~100mK and are surrounded by a cold enclosure at ~1K. Both the arrays and cold enclosure are cooled by a novel, liquid cryogen-free dilution refrigerator. To reduce the thermal background on the arrays to a minimum the main optics structure, weighing in excess of 450kg, must be cooled to less than 15K. A pair of low vibration pulse tube coolers are used to cool this structure and a radiation shield at ~60K. This paper describes the cryo-mechanical design of SCUBA-2 and discusses some of the issues and techniques needed to both cool the instrument within a reasonable timescale, and operate it in the required temperature regime