The Probe of Inflation and Cosmic Origins (PICO) is a probe-class mission concept currently under study by NASA. PICO will probe the physics of the Big Bang and the energy scale of inflation, constrain the sum of neutrino masses, measure the growth of structures in the universe, and constrain its reionization history by making full sky maps of the cosmic microwave background with sensitivity 80 times higher than the <i>Planck</i> space mission. With bands at 21-799 GHz and arcmin resolution at the highest frequencies, PICO will make polarization maps of Galactic synchrotron and dust emission to observe the role of magnetic fields in Milky Way's evolution and star formation. We discuss PICO's optical system, focal plane, and give current best case noise estimates. The optical design is a two-reflector optimized open-Dragone design with a cold aperture stop. It gives a diffraction limited field of view (DLFOV) with throughput of 910 cm<sup>2</sup>sr at 21 GHz. The large 82 square degree DLFOV hosts 12,996 transition edge sensor bolometers distributed in 21 frequency bands and maintained at 0.1 K. We use focal plane technologies that are currently implemented on operating CMB instruments including three-color multi-chroic pixels and multiplexed readouts. To our knowledge, this is the first use of an open-Dragone design for mm-wave astrophysical observations, and the only monolithic CMB instrument to have such a broad frequency coverage. With current best case estimate polarization depth of 0.65 µKCMB-arcmin over the entire sky, PICO is the most sensitive CMB instrument designed to date.
The Origins Space Telescope (OST) is a NASA study for a large satellite mission to be submitted to the 2020 Decadal Review. The proposed satellite has a fleet of instruments including the HEterodyne Receivers for OST (HERO). HERO is designed around the quest to follow the trail of water from the ISM to disks around protostars and planets. HERO will perform high-spectral resolution measurements with 2x9 pixel focal plane arrays at any frequency between 468GHz to 2,700GHz (617 to 111 μm). HERO builds on the successful Herschel/HIFI heritage, as well as recent technological innovations, allowing it to surpass any prior heterodyne instrument in terms of sensitivity and spectral coverage.
The compelling science case for the observation of B-mode polarization in the cosmic microwave background (CMB) is driving the CMB community to expand the observed sky fraction, either by extending survey sizes or by deploying receivers to potential new northern sites. For ground-based CMB instruments, poorly-mixed atmospheric water vapor constitutes the primary source of short-term sky noise. This results in short-timescale brightness fluctuations, which must be rejected by some form of modulation. To maximize the sensitivity of ground-based CMB observations, it is useful to understand the effects of atmospheric water vapor over timescales and angular scales relevant for CMB polarization measurements. To this end, we have undertaken a campaign to perform a coordinated characterization of current and potential future observing sites using scanning 183 GHz water vapor radiometers (WVRs). So far, we have deployed two identical WVR units; one at South Pole, Antarctica, and the other at Summit Station, Greenland. The former site has a long heritage of ground based CMB observations and is the current location of the Bicep/Keck Array telescopes and the South Pole Telescope. The latter site, though less well characterized, is under consideration as a northern-hemisphere location for future CMB receivers. Data collection from this campaign began in January 2016 at South Pole and July 2016 at Summit Station. Data analysis is ongoing to reduce the data to a single spatial and temporal statistic that can be used for one-to-one site comparison.
The CCAT-prime telescope is a 6-meter aperture, crossed-Dragone telescope, designed for millimeter and sub-millimeter wavelength observations. It will be located at an altitude of 5600 meters, just below the summit of Cerro Chajnantor in the high Atacama region of Chile. The telescope’s unobscured optics deliver a field of view of almost 8 degrees over a large, flat focal plane, enabling it to accommodate current and future instrumentation fielding <100k diffraction-limited beams for wavelengths less than a millimeter. The mount is a novel design with the aluminum-tiled mirrors nested inside the telescope structure. The elevation housing has an integrated shutter that can enclose the mirrors, protecting them from inclement weather. The telescope is designed to co-host multiple instruments over its nominal 15 year lifetime. It will be operated remotely, requiring minimum maintenance and on-site activities due to the harsh working conditions on the mountain. The design utilizes nickel-iron alloy (Invar) and carbon-fiber-reinforced polymer (CFRP) materials in the mirror support structure, achieving a relatively temperature-insensitive mount. We discuss requirements, specifications, critical design elements, and the expected performance of the CCAT-prime telescope. The telescope is being built by CCAT Observatory, Inc., a corporation formed by an international partnership of universities. More information about CCAT and the CCAT-prime telescope can be found at www.ccatobservatory.org.
A common optical design for a coma-corrected, 6-meter aperture, crossed-Dragone telescope has been adopted for the CCAT-prime telescope of CCAT Observatory, Inc., and for the Large Aperture Telescope of the Simons Observatory. Both are to be built in the high altitude Atacama Desert in Chile for submillimeter and millimeter wavelength observations, respectively. The design delivers a high throughput, relatively flat focal plane, with a field of view 7.8 degrees in diameter for 3 mm wavelengths, and the ability to illuminate >100k diffraction-limited beams for < 1 mm wavelengths. The optics consist of offset reflecting primary and secondary surfaces arranged in such a way as to satisfy the Mizuguchi-Dragone criterion, suppressing first-order astigmatism and maintaining high polarization purity. The surface shapes are perturbed from their standard conic forms in order to correct coma aberrations. We discuss the optical design, performance, and tolerancing sensitivity. More information about CCAT-prime can be found at ccatobservatory.org and about Simons Observatory at simonsobservatory.org.
Atacama Large Millimeter/submillimeter Array (ALMA) is the world’s largest millimeter/ submillimeter (mm / Submm) interferometer. Along with science observations, ALMA has performed several long baseline campaigns in the last 6 years to characterize and optimize its long baseline capabilities. To achieve full long baseline capability of ALMA, it is important to understand the characteristics of atmospheric phase fluctuation at long baselines, since it is believed to be the main cause of mm/submm image degradation. For the first time, we present detailed properties of atmospheric phase fluctuation at mm/submm wavelength from baselines up to 15 km in length. Atmospheric phase fluctuation increases as a function of baseline length with a power-law slope close to 0.6, and many of the data display a shallower slope (02.-03) at baseline length greater than about 15 km. Some of the data, on the other hand, show a single slope up to the maximum baseline length of around 15 km. The phase correction method based on water vapor radiometers (WVRs) works well, especially for cases with precipitable water vapor (PWV) greater than 1 mm, typically yielding a 50% decrease or more in the degree of phase fluctuation. However, signicant amount of atmospheric phase fluctuation still remains after the WVR phase correction: about 200 micron in rms excess path length (rms phase fluctuation in unit of length) even at PWV less than 1 mm. This result suggests the existence of other non-water-vapor sources of phase fluctuation. and emphasizes the need for additional phase correction methods, such as band-to-band and/or fast switching.
The ALMA (Atacama Large Millimeter/submillimeter Array) radio interferometer has some different types of antennas which have a variation of gain and leakages across the primary beam of an individual antenna. We have been developing an artificial calibration source which is used for compensation of individual difference of antennas. In a high-frequency antenna, using astronomical sources to do calibration measurement would be extremely time consuming, whereas with the artificial calibration source becomes a realistic possibility. Photonic techniques are considered to be superior to conventional techniques based on electronic devices in terms of wide bandwidth and high-frequency signals. Conversion from an optical signal to a millimeter/sub-millimeter wave signal is done by a photo-mixer.
We present the temporal phase stability of the entire ALMA system. We first verified the temporal phase stability: We observed a strong quasar for a long time (a few tens of minutes), derived the temporal structure function after the atmospheric phase correction using the water vapor radiometers (WVRs), and confirmed that the phase stability of all the baselines reached the ALMA specification. We then verified frequency transfer between bands: We observed a bright quasar and switched between the two frequency bands, and confirmed that the phase returned to the original values within the phase fluctuation. In addition to these results, we also studied the effectiveness of the WVR phase correction at various frequencies, baseline lengths, and weather conditions.
The Atacama Large Millimeter/submillimeter Array (ALMA) is an international facility at an advanced stage of
construction in the Atacama region of northern Chile. ALMA will consist of two arrays of high-precision antennas: one
made up of twelve 7-meter diameter antennas operating in closely-packed configurations of about 50m in diameter, and
the other of up to sixty-four 12-meter antennas arranged in configurations with diameters ranging from about 150 meters
to 15 km. There will be four more 12-meter antennas to provide the "zero-spacing" information, which is critical for
making accurate images of extended objects. The antennas will be equipped with sensitive millimeter-wave receivers
covering most of the frequency range 84 to 950 GHz. State-of-the-art microwave, digital, photonic and software systems
will capture the signals, transfer them to the central building and correlate them, while maintaining accurate
synchronization. ALMA will provide images of a wide range of astronomical objects with great sensitivity and very
high spectral resolution. The images will have much higher "fidelity" than those from existing mm/submm telescopes.
This paper gives an update on the status of construction and on progress with the testing and scientific commissioning.
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 Atacama Large Millimeter/submillimeter Array (ALMA) is an international radio telescope under construction in
the Atacama Desert of northern Chile. ALMA will be situated on a high-altitude site at 5000 m elevation, allowing
excellent atmospheric transmission over the instrument wavelength range of 0.3 to 3 mm. ALMA will contain an array
of up to sixty-four 12-m diameter high-precision antennas arranged in multiple configurations ranging in size from 150
meters up to ~15 km, and a set of four 12-m and twelve 7-m antennas operating in closely packed configurations ~50m
in diameter. The instrument will provide both interferometric and total-power astronomical information on high-energy
electrons, molecular gas and dust in solar system, our Galaxy, and the nearby and high-redshift universe. In this paper
we outline the scientific drivers, technical challenges and construction status of ALMA.
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
We discuss the use of the water vapour radiometry technique for atmospheric phase correction as applied to the Atacama Large Millimetre Array (ALMA). The atmospheric conditions derived from site test instrumentation are summarised, and the nature of the phase correction problem quantified. We then present calculations of the expected errors in the radiometrically-corrected atmospheric phase, based on estimates of the radiometer sensitivity. These results indicate how well we need to know the atmospheric structure in order to make accurate phase estimates, and have implications for the meteorological instruments needed on the site. Finally we present the results of simulations of daytime turbulence on the site, and use these to predict the phase fluctuations due to wet and dry air, and discuss their implications for phase correction at Chajnantor.
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.
We present a physical optics analysis of the Heterodyne Array Receiver Program B-band (HARP-B) receiver for the James Clerk Maxwell Telescope (JCMT). Three sets of calculations are performed:
1. A Gaussian beam analysis to determine grid sizes for the Mach-Zehnder polarising interferometer. It is shown that an optimum grid size of 150mm clear diameter has little effect on the beam pattern and transmission of power through the system.
2. A Model of the HARP-B Imaging array is created using an ideal beam pattern for the corrugated feed. This produces an accurate beam pattern of minimal distortion.
3. The throughput and beam patterns for the whole HARP-B system are calculated. This produced beam patterns showing a high degree of symmetry with acceptable power coupling to the reflectors.
The Kolner Observatorium fur Submillimeter-Astronomie (KOSMA) has recently been equipped with a new 3 m submm telescope. The new telescope dish has a CFRP backstructure and aluminum panels with a mean surface accuracy of the individual panels of well below 10 micrometer. The 18 panels of the primary reflector have been adjusted to a surface rms of at present about 30 micrometer with the help of a holographic phase retrieval algorithm developed for and previously used at the JCMT. The present main beam efficiency derived from observations of Jupiter and Saturn is approximately 45% at 660 GHz. The new telescope features a chopping secondary and 2 Nasmyth ports. The excellent atmospheric transmission during winter time at the telescope site, Gornergrat near Zermatt, Switzerland, allow us flexible operation up to the highest atmospheric submm windows. We present the current status of the new telescope, in particular with regard to its surface alignment, and first astronomical results at 660 and 690 GHz.
The main features of recent antenna designs are reviewed. Particular reference is made to the challenges presented by the large aperture-synthesis array projects now under development. In the final section some specific problems concerned with holographic antenna measurements are discussed.
The Caltech Submillimeter Observatory and the James Clerk Maxwell Telescope have been combined to form the only astronomical interferometer currently operating at submillimeter wavelengths. The telescopes have been operating in this mode for one or two dedicated periods in each of the last 5 years. Results with sub-arcsecond resolution have been obtained at 230, 345 and 460 GHz. The interferometer differs in many ways from the existing millimeter-wave arrays. Connecting two independent telescopes of different design introduces extra problems not encountered with homogeneous arrays of antennas. The CSO-JCMT system is described, with an emphasis on these incompatibility issues and solutions that were adopted. Analysis of data from a single, fixed baseline requires direct modeling of the measured visibilities rather than a synthesized image, an approach that has since proved invaluable for analyzing data from other arrays as well. The sensitivity and angular resolution of the interferometer are limited by fluctuations in the refractive index due to water vapor in the Earth's atmosphere. Two water vapor radiometers have been designed, built and installed to monitor the fluctuations in each beam and generate a correction to the visibility phase measured by the interferometer. These radiometers are described and recent results are presented.