A three-cartridge cryogenic receiver system is constructed for the Greenland Telescope Project. The system is equipped with a set of sub-millimeter receivers operating at 86, 230, and 345 GHz, as well as a complete set of instruments for calibration, control and monitoring. It is single pixel instrument built for VLBI observations. With the receiver system, the GLT has completed commissioning of its 12-m sub-millimeter antenna and participated in global very-long-baseline interferometry (VLBI) observations at Thule Air Base (TAB). This paper describes the receiver specification, construction, and verification.
The Sub-millimeter Common-User Bolometer Array 2 (SCUBA-2) large format Transition Edge Sensor (TES) arrays are optimized to maximize mapping speed with two commissioned regular observing scan patterns. The ancillary instruments POLarimeter 2 (POL-2) and Fourier Transform Spectrometer 2 (FTS-2) impose different demands on the arrays compared to regular stand-alone SCUBA-2 observing. This includes a change in the background optical power loading on the arrays and a requirement for a larger dynamic range from the individual TES bolometers. In this paper, we discuss the process for optimizing the TES arrays specifically for POL-2 and FTS-2 operations and report the improvements that we have obtained.
The Greenland Telescope project has recently participated in an experiment to image the supermassive black hole shadow at the center of M87 using Very Long Baseline Interferometry technique in April of 2018. The antenna consists of the 12-m ALMA North American prototype antenna that was modified to support two auxiliary side containers and to withstand an extremely cold environment. The telescope is currently at Thule Air Base in Greenland with the long-term goal to move the telescope over the Greenland ice sheet to Summit Station. The GLT currently has a single cryostat which houses three dual polarization receivers that cover 84-96 GHz, 213-243 GHz and 271-377 GHz bands. A hydrogen maser frequency source in conjunction with high frequency synthesizers are used to generate the local oscillator references for the receivers. The intermediate frequency outputs of each receiver cover 4-8 GHz and are heterodyned to baseband for digitization within a set of ROACH-2 units then formatted for recording onto Mark-6 data recorders. A separate set of ROACH-2 units operating in parallel provides the function of auto-correlation for real-time spectral analysis. Due to the stringent instrumental stability requirements for interferometry a diagnostic test system was incorporated into the design. Tying all of the above equipment together is the fiber optic system designed to operate in a low temperature environment and scalable to accommodate a larger distance between the control module and telescope for Summit Station. A report on the progress of the above electronics instrumentation system will be provided.
The Greenland Telescope (GLT) project and the East Asian Observatory (EAO) successfully commissioned the first light GLT instrument at the James Clerk Maxwell Telescope (JCMT) in Hawaii, prior to transferring the instrument to Greenland. The GLT instrument which comprises of a cryostat with three cartridge-type receivers (at 86GHz, 230GHz and 345GHz) was installed into the receiver cabin of JCMT and operated in three modes: - (a) Regular JCMT observing with the GLT instrument, using ACSIS, (JCMT’s autocorrelation spectrometer) as the backend and JCMT software for telescope control, data reduction, pointing and antenna focus adjustment. (b) Single dish observations of astronomical spectral line sources, recording data onto mark 6 recorders for offline data reduction. (c) eSMA interferometer array observations at 230GHz in conjunction with the SMA. In this paper, we report on the installation and integration of the GLT instrument at JCMT, present results from commissioning and show how the success of the GLT instrument commissioning fits with our plans for future instrumentation at JCMT.
Sub-millimeter polarization observations using the POL-2 instrument mounted on the dual wavelength (850/450 μm) 10 k pixel sub-millimeter camera SCUBA-2 is in high demand on the James Clerk Maxwell Telescope (JCMT). The high level of Instrumental Polarization (IP) generated by the Gore-TexTM wind blind protecting the telescope is a hampering factor for these observations. The wind blind both introduces an overall linear polarization and a four lobed polarization footprint seen on strong point sources after removal of a beam averaged IP. During commissioning an IP model was developed for the 850 μm band but a good 450 μm model was lacking. This paper describes the effort to improve the 850 μm IP model, establish a 450 μm model and the work to understand and model the IP. During the work the wind blind was removed for a month to isolate the contribution of the wind blind from other sources of the IP. A theoretical model for the non wind blind generated IP has been developed. However, a theoretical model for the wind blind IP is still being worked on.
The Greenland Telescope Project (GLT) has successfully commissioned its 12-m sub-millimeter. In January 2018, the fringes were detected between the GLT and the Atacama Large Millimeter Array (ALMA) during a very-long-baseline interferometry (VLBI) exercise. In April 2018, the telescope participated in global VLBI science observations at Thule Air Base (TAB). The telescope has been completely rebuilt, with many new components, from the ALMA NA (North America) Prototype antenna and equipped with a new set of sub-millimeter receivers operating at 86, 230, and 345 GHz, as well as a complete set of instruments and VLBI backends. This paper describes our progress and status of the project and its plan for the coming decade.
The Greenland Telescope completed its construction, so the commissioning phase has been started since December 2017. Single-dish commissioning has started from the optical pointing which produced the first pointing model, followed by the radio pointing and focusing using the Moon for both the 86 GHz and the 230 GHz receivers. After Venus started to rise from the horizon, the focus positions has been improved for both receivers. Once we started the line pointing using the SiO(2-1) maser line and the CO(2-1) line for the 86 GHz and the 230 GHz receivers, respectively, the pointing accuracy also improved, and the final pointing accuracy turned to be around 3" - 5" for both receivers. In parallel, VLBI commissioning has been performed, with checking the frequency accuracy and the phase stability for all the components that would be used for the VLBI observations. After all the checks, we successfully joined the dress rehearsals and actual observations of the 86 GHz and 230 GHz VLBI observations, The first dress rehearsal data between GLT and ALMA were correlated, and successfully detected the first fringe, which confirmed that the GLT commissioning was successfully performed.
We describe the control and monitoring system for the Greenland Telescope (GLT). The GLT is a 12-m radio telescope aiming to carry out the sub-millimeter Very Long Baseline Interferometry (VLBI) observations and image the shadow of the super massive black hole in M87. In November 2017 construction has been finished and commissioning activity has been started. In April 2018 we participated in the VLBI observing campaign for the Event Horizon Telescope (EHT) collaboration. In this paper we present the entire GLT control/monitoring system in terms of computers, network and software.
Under the new operational purview of the East Asian Observatory, the JCMT continues to produce premier wide-field submillimetre science. Now the Observatory looks to embark on an ambitious series of instrumentation upgrades and opportunities to keep the telescope at the bleeding edge of its performance capabilities, whilst harnessing the collaborative expertise of the participating EAO regions and its JCMT partners. New heterodyne instruments include a new receiver at 230 GHz, a super array (90 pixels) at 345 GHz and the upgrade possibilities for the continuum camera SCUBA-2. In addition, the opportunities for PI and visiting instruments, including TimePilot and Gismo-2 will be described.
SCUBA-2 is a state of the art wide field camera on the JCMT. SCUBA-2 has been fully operational since November
2011, producing a wide range of science results, including a unique series of survey programs. A new large survey
programme commenced in 2015, which included for the first time, polarisation sensitive measurements using POL-2, the
polarimeter ancillary instrument. We discuss proposals and the science case for upgrading SCUBA-2 with new detector
arrays that will keep SCUBA-2 and the JCMT at the forefront of continuum submillimetre science.
As part of the JCMT Future Instrumentation Project, the EAO looks to optimize the premier niche of the facility as the
go-to telescope for fast, deep wide-field mapping of the universe at 345 GHz (850 um). The next generation heterodyne
array for JCMT will be designed to provide deep ultra-fast mapping capabilities that takes advantage of the full field-of-view
available to the telescope, and an array of 90 SIS mixers. This paper presents a preliminary design options and the
critical science drivers for the project.
The POL-2 polarimeter for the SCUBA-2 10 000 pixel Terahertz camera on the James Clerk Maxwell Telescope
(JCMT) in it's late state of commissioning. Proposals have been accepted for POL-2 and general observing will
start in August 2016. SCUBA-2 has a field of view of 43 arcmin at both of the 850 and 450 μm focal planes.
POL-2 will map the sky in the the 850 μm band. The POL-2 polarimeter utilizes three optical components: a
half wave plate and two wire-grid polarizers used as calibrator and analyzer covering the full field of SCUBA-2.
We describe the instrument, data acquisition and features/artifacts that have been encountered during the
The newly formed East Asian Observatory assumed operations of the James Clerk Maxwell Telescope in March of 2015. In just three weeks, the facility needed to run up completely mothballed observatory operations, introduce the telescope to a vast new scientist base with no familiarity with the facility, and create a non-existent science program. The handover to the EAO has since been a succession of challenging time-lines, and nearly unique problems requiring novel solutions. The results, however, have been spectacular, with subscription rates at unprecedented levels, a new series of Large Programs underway, as well as an exciting Future Instrumentation Project that together promises to keep JCMT at the forefront of wide-field submillimeter astronomy for the next decade.
instrument’s twin focal planes, each with over 5000 superconducting Transition Edge Sensors (TES) that work simultaneously at 450 and 850 microns are producing excellent science results and in particular a unique series of JCMT legacy surveys. In this paper we give an update on the performance of the instrument over the past 2 years of science operations and present the results of a study into the noise properties of the TES arrays. We highlight changes that have been implemented to increase the efficiency and performance of SCUBA-2 and discus the potential for future enhancements.
The James Clerk Maxwell Telescope (JCMT) is the largest single-dish submillimetre telescope in the world, and throughout its lifetime the volume and impact of its science output have steadily increased. A key factor for this continuing productivity is an ever-evolving approach to optimising operations, data acquisition, and science product pipelines and archives. The JCMT was one of the first common-user telescopes to adopt flexible scheduling in 2003, and its impact over a decade of observing will be presented. The introduction of an advanced data-reduction pipeline played an integral role, both for fast real-time reduction during observing, and for science-grade reduction in support of individual projects, legacy surveys, and the JCMT Science Archive. More recently, these foundations have facilitated the commencement of remote observing in addition to traditional on-site operations to further increase on-sky science time. The contribution of highly-trained and engaged operators, support and technical staff to efficient operations will be described. The long-term returns of this evolution are presented here, noting they were achieved in face of external pressures for leaner operating budgets and reduced staffing levels. In an era when visiting observers are being phased out of many observatories, we argue that maintaining a critical level of observer participation is vital to improving and maintaining scientific productivity and facility longevity.
SCUBA-2 is a wide-field submillimeter bolometer camera operating at the James Clerk Maxwell Telescope. The camera has twin focal planes, each with 5120 superconducting Transition Edge Sensors, which provide simultaneous images in two filter bands at 450 and 850 microns matched to the atmospheric windows. Detailed knowledge of the optical filter profiles that define these bands is important for estimating potential contamination from the prevalent CO J = 3-2 and CO 6-5 line emission, and correctly interpreting the effects of the source spectral index on photometric observations. We present measurements of the spectral response of SCUBA-2 obtained with FTS-2, the ancillary Fourier transform spectrometer instrument at the JCMT. The spectral measurements will be compared with the predicted filter profile determined from the linear combination of the individual filter profiles present in the SCUBA-2 optical train.
We present the latest commissioning results and instrument performance for the SCUBA-2 imaging Fourier Transform Spectrometer (FTS-2) installed at the James Clerk Maxwell Telescope (JCMT). This ancillary instrument provides intermediate spectral resolution (R ~10 to 5000) across both the 450 and 850 μm atmospheric transmission windows with a FOV of ~5 arcmin2. The superconducting TES sensors and SQUID readout of SCUBA-2 present unique challenges for operation of an FTS; the sensitivity requirements demand high detector linearity and stability in addition to control of systematic atmospheric and optical spillover effects. We discuss the challenges encountered during commissioning and ongoing efforts to mitigate their effects.
SCUBA-2 is the largest submillimetre wide-field bolometric camera ever built. This 43 square arc- minute field-of-view instrument operates at two wavelengths (850 and 450 microns) and has been installed on the James Clerk Maxwell Telescope on Mauna Kea, Hawaii. SCUBA-2 has been successfully commissioned and operational for general science since October 2011. This paper presents an overview of the on-sky performance of the instrument during and since commissioning in mid- 2011. The on-sky noise characteristics and NEPs of the 450 μm and 850 μm arrays, with average yields of approximately 3400 bolometers at each wavelength, will be shown. The observing modes of the instrument and the on-sky calibration techniques are described. The culmination of these efforts has resulted in a scientifically powerful mapping camera with sensitivities that allow a square degree of sky to be mapped to 10 mJy/beam rms at 850 μm in 2 hours and 60 mJy/beam rms at 450 μm in 5 hours in the best weather.
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.
The James Clerk Maxwell Telescope (JCMT) Telescope Control System (TCS) received significant upgrades to provide
new observing capabilities to support the requirements of the SCUBA-2 instrument. The core of the TCS is the Portable
Telescope Control System (PTCS), which was developed through collaboration between the Joint Astronomy Centre and
the Anglo-Australian Observatory. The PTCS provides a well-designed virtual telescope function library that simplifies
these sorts of upgrades. The TCS was previously upgraded to provide the required scanning modes for the JCMT
heterodyne instruments. The heterodyne instruments required only relatively simple raster or boustrophedon patterns,
which are basically composed of multiple straight-line scans to cover a rectangular area. The most recent upgrades built
upon those heterodyne scanning modes to satisfy the SCUBA-2 requirements. With these upgrades, the TCS can scan
the telescope in any pattern that can be described as a continuous function of time. This new capability has been utilized
during the current SCUBA-2 on-sky commissioning phase to scan the telescope in a variety of patterns (Lissajous, pong,
ellipse, and daisy) on the sky. This paper will give a brief description of the PTCS, provide information on the selection
of the SCUBA-2 scanning modes, describe the changes to the TCS that were necessary to implement the new scanning
modes, and show the performance of the telescope during SCUBA-2 commissioning.
Commissioning of SCUBA-2 included a program of skydips and observations of calibration sources intended to
be folded into regular observing as standard methods of source flux calibration and to monitor the atmospheric
opacity and stability. During commissioning, it was found that these methods could also be utilised to characterise
the fundamental instrument response to sky noise and astronomical signals. Novel techniques for analysing onsky
performance and atmospheric conditions are presented, along with results from the calibration observations
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.
This paper describes the key design features and performance of HARP, an innovative heterodyne focal-plane array
receiver designed and built to operate in the submillimetre on the James Clerk Maxwell Telescope (JCMT) in Hawaii.
The 4x4 element array uses SIS detectors, and is the first sub-millimetre spectral imaging system on the JCMT. HARP
provides 3-dimensional imaging capability with high sensitivity at 325-375 GHz and affords significantly improved
productivity in terms of speed of mapping. HARP was designed and built as a collaborative project between the
Cavendish Astrophysics Group in Cambridge UK, the UK-Astronomy Technology Centre in Edinburgh UK, the
Herzberg Institute of Astrophysics in Canada and the Joint Astronomy Centre in Hawaii. SIS devices for the mixers were
fabricated to a Cavendish Astrophysics Group design at the Delft University of Technology in the Netherlands. Working
in conjunction with the new Auto Correlation Spectral Imaging System (ACSIS), first light with HARP was achieved in
December 2005. HARP synthesizes a number of interesting features across all elements of the design; we present key
performance characteristics and images of astronomical observations obtained during commissioning.
The eSMA ("expanded SMA") combines the SMA, JCMT and CSO into a single facility, providing enhanced sensitivity
and spatial resolution owing to the increased collecting area at the longest baselines. Until ALMA early
science observing (2011), the eSMA will be the facility capable of the highest angular resolution observations at
345 GHz. The gain in sensitivity and resolution will bring new insights in a variety of fields, such as protoplanetary/
transition disks, high-mass star formation, solar system bodies, nearby and high-z galaxies. Therefore the
eSMA is an important facility to prepare the grounds for ALMA and train scientists in the techniques.
Over the last two years, and especially since November 2006, there has been substantial progress toward
making the eSMA into a working interferometer. In particular, (i) new 345-GHz receivers, that match the
capabilities of the SMA system, were installed at the JCMT and CSO; (ii) numerous tests have been performed
for receiver, correlator and baseline calibrations in order to determine and take into account the effects arising
from the differences between the three types of antennas; (iii) First fringes at 345 GHz were obtained on August
30 2007, and the array has entered the science-verification stage.
We report on the characteristics of the eSMA and its measured performance at 230 GHz and that expected
at 345 GHz. We also present the results of the commissioning and some initial science-verification observations,
including the first absorption measurement of the C/CO ratio in a galaxy at z=0.89, located along the line of sight to the lensed quasar PKS 1830-211, and on the imaging of the vibrationally excited HCN line towards
A 183GHz water vapour radiometer is installed at the JCMT, but is not currently used for active atmospheric
calibration. With the installation of the SCUBA-2 submillimetre camera, it is desirable to provide more accurate
and time-sensitive calibration at specific wavelengths. It is shown here that the 183GHz water vapour monitor
data can be used to calculate the atmospheric opacity over small time-scales, directly along the line-of-sight of
the instrument. These data will be used to identify the potential for improvement in existing calibration schemes,
and the requirements of such a system if used with an instrument such as SCUBA-2.
A 350GHz 4 × 4 element heterodyne focal plane array using SIS detectors is presently being constructed for the JCMT. The construction is being carried out by a collaborative group led by the MRAO, part of the Astrophysics Group, Cavendish Laboratory, in conjunction with the UK-Astronomy Technology Centre (UK-ATC), The Herzberg Institute of Astrophysics (HIA) and the Joint Astronomy Center (JAC). The Delft Institute of Microelectronics & Sub-micron Technology (DIMES) is fabricating junctions for the SIS mixers that have been designed at MRAO.
Working in conjunction with the 'ACSIS' correlator & imaging system, HARP-B will provide 3-dimensional imaging capability with high sensitivity at 325 to 375GHz. This will be the first sub-mm spectral imaging system on JCMT - complementing the continuum imaging capability of SCUBA - and affording significantly improved productivity in terms of speed of mapping. The core specification for the array is that the combination of the receiver noise temperature and beam efficiency, weighted optimally across the array will be <330K SSB for the central 20GHz of the tuning range.
In technological terms, HARP-B synthesizes a number of interesting and innovative features across all elements of the design. This paper presents both a technical and organizational overview of the HARP-B project and gives a description of all of the key design features of the instrument. 'First light' on the instrument is currently anticipated in spring 2004.
Many telescope control systems now make use of the so-called 'virtual telescope' concept -- a software abstraction of the real telescope which masks imperfections in the hardware from higher levels of the software. In general, this approach allows for elegant and rigorous control of telescope pointing and tracking. When slewing, however, while the virtual telescope arrives on source immediately, the real telescope only catches up after some time. This is especially a problem when performing raster-scanned observations: since the demand position and velocity have discontinuities at the end of each row, a naive implementation of the standard virtual telescope system results in missing the demand positions at the start of each row. In the existing JCMT telescope control system (TCS), this problem is solved by having the TCS calculate a route in (az,el) space for the real telescope to follow which results in it arriving at the correct position, moving with the correct velocity, at a predictable time in the future. In this paper we describe a generalized implementation of this technique, which has the added advantage that the 'astrometric kernel' and 'telescope servo' layers are cleanly separated, allowing telescope-specific hardware to be combined with a generic astrometric kernel. Since the solution requires only minimal changes to the standard virtual telescope design, this approach may be of interest to other telescopes which are currently using, or are planning to use that design.