The National Radio Astronomy Observatory (NRAO) has engaged the broad scientific and technical communities in the design of a next-generation Very Large Array [1] (ngVLA), a large-scale research infrastructure project under development for the National Science Foundation Astronomical Sciences Division (NSF-AST) through a cooperative agreement with Associated Universities, Inc. The ngVLA is envisaged as an interferometric array with ten times greater sensitivity and spatial resolution than the current VLA and ALMA, operating in the frequency range of 1.2 - 116 GHz. Replacing both the VLA and VLBA, the ngVLA will be an open-skies, transformative, multi-disciplinary scientific instrument opening a new window on the Universe through ultra-sensitive imaging of thermal line and continuum emission down to milliarcsecond-scale resolution, as well as unprecedented broad-band continuum polarimetric imaging of non-thermal processes. The ngVLA will be optimized for observations in the spectral region between the superb performance of ALMA at sub-mm wavelengths, and the future Phase I Square Kilometer Array (SKA-1) at decimeter and longer wavelengths, resulting in a transformational instrument for the entire scientific community. In 2019, the ngVLA project completed the public release of the ngVLA Reference Design [2][3] as the technical and cost basis of the ngVLA Astro2020 Decadal Survey proposal [4]. With a strong endorsement of the facility concept by the Decadal Survey [5] and continued support from the National Science Foundation, the project is preparing for a System Conceptual Design Review in the spring of 2022. This paper provides a technical update, noting technical advancements and changes to the design baseline.
The next-generation Very Large Array (ngVLA) is an astronomical observatory planned to operate at centimeter wavelengths (25 to 0.26 centimeters, corresponding to a frequency range extending from 1.2 GHz to 116 GHz). The observatory will be a synthesis radio telescope constituted of approximately 214 reflector antennas each of 18 meters diameter, operating in a phased or interferometric mode.
We provide an overview of the current system design of the ngVLA. The concepts for major system elements such as the antenna, receiving electronics, and central signal processing are presented. We also describe the major development activities that are presently underway to advance the design.
The North American astronomical community is considering a future large area radio array optimized to perform imaging of thermal emission down to milliarcsecond scales. This `Next Generation Very Large Array' would entail ten times the effective collecting area of the Jansky Very Large Array, operate from 1GHz to 115GHz, with ten times longer baselines (300km) providing milliarcsecond resolution, and include a dense core on kilometer scales for high surface brightness imaging. The preliminary design, capabilities, and some of the priority science goals of the instrument are summarized.
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.
KEYWORDS: Antennas, Astronomy, Optical correlators, Receivers, Signal processing, Calibration, Data archive systems, Digital signal processing, Galactic astronomy, Interferometry
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 which provides excellent atmospheric transmission over the instrument wavelength range of 0.3 to 3 mm. ALMA will be comprised of two key observing components - an array of up to sixty-four 12-m diameter antennas arranged in a multiple configurations ranging in size from 0.15 to ~14 km, and a set of four 12-m and twelve 7-m antennas operating in closely-packed configurations ~50m in diameter (known as the Atacama Compact Array, or ACA), providing both interferometric and total-power astronomical information. High-sensitivity dual-polarization 8 GHz-bandwidth spectral-line and continuum measurements between all antennas will be available from two flexible digital correlators. At the shortest planned wavelength and largest configuration, the angular resolution of ALMA will be 0.005". The instrument will use superconducting (SIS) mixers to provide the lowest possible receiver noise contribution, and special-purpose water vapor radiometers to assist in calibration of atmospheric phase distortions. A complex optical fiber network will transmit the digitized astronomical signals from the antennas to the correlators in the Array Operations Site Technical Building, and post-correlation to the lower-altitude Operations Support Facility (OSF) data archive. Array control, and initial construction and maintenance of the instrument, will also take place at the OSF. ALMA Regional Centers in the US, Europe and Japan will provide the scientific portals for the use of ALMA; a call for early science observations is expected in 2009. In this paper, we present the status of the ALMA project as of mid 2006.
A new Combined Array for Research in Millimeter-wave Astronomy (CARMA) interferometer is being assembled from the existing Owens Valley Radio Observatory (OVRO), the Berkeley-Illinois-Maryland Association (BIMA) millimeter interferometers and the new Sunyaev?Zeldovich Array (SZA) at Cedar Flat, a site at 2,200 m altitude in the Inyo Mountains east of OVRO. The array will consist of 23 antennas of three different diameters, 3.5, 6.1 and 10.4 m, and will support observations in the 1 cm, 3 mm and 1.3 mm bands. The fist-light correlator is a flexible FPGA based system that will process up to 8 GHz of bandwidth on the sky for two subarrays consisting of 8 and 15 elements. The array configurations will offer antenna spacings from 5 m to 1.9 km allowing unprecedented high resolution and wide field imaging at millimeter wavelengths. Radiometers observing the 22 GHz water vapor emission line will be used to measure and correct for the water vapor induced path delay along the line of sight for each telescope and thereby minimize the time lost to “bad seeing”. This university based facility will emphasize technology development and student training along with leading edge astronomical research in areas ranging from Sunyaev-Zeldovich effect galaxy cluster surveys to studying protoplanetary disks.
The Combined Array for Research in Millimeter-wave Astronomy (CARMA) is a 23-antenna heterogeneous millimeter array under construction in the White/Inyo Mountains of eastern California. CARMA will merge the existing Owens Valley and Berkeley-Illinois-Maryland Association arrays into a single instrument focusing on pure research, technology development and student training. A new high-altitude site will enable routine 205-265 GHz observing, and may allow observations in the 345 GHz window. Eight additional 3.5-m antennas from the University of Chicago will also be integrated into CARMA when not imaging the Sunyaev-Zel'dovich effect towards clusters of galaxies.
At first light, the array will observe at 12, 3 and 1.3 mm using a mix of SIS and MMIC-based receivers. A new, highly flexible correlator incorporating reprogrammable FPGA technology will process configurable subsets of the antennas specified according to the science objectives. Leading-edge water vapor radiometers will be used to correct for atmospheric opacity and signal phase fluctuations. CARMA will be capable of both high resolution and wide-field imaging, covering a range of angular scales unmatched by any current or planned millimeter-wave instrument. The high sensitivity, sub-arcsecond angular resolution and excellent uv-coverage of CARMA will ensure major advances in studies of the universe. The array will provide high-fidelity resolved images of solar-system objects, protostars, protoplanetary disks, and galaxies both nearby and at high redshift - directly addressing many key research areas in astronomy and astrophysics.
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