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تسجيل مستخدم جديدThe ALMA Development Program: Roadmap to 2030
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John Carpenter
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The Atacama Large Millimeter/submillimeter Array (ALMA) is the premier telescope for sensitive, high-resolution observations at millimeter and submillimeter wavelengths. The array consists of fifty 12-m diameter antennas that can be reconfigured to baselines as long as 16 km, twelve 7-m antennas that sample the short visibility spacings, and four 12-m antennas that provide total power capabilities for spectral line and continuum observations. Located in the Atacama desert in northern Chile at an elevation of 5000 m on the Chajnantour plateau, the ALMA site provides excellent observing conditions with low precipitable water vapor. The large number of antennas, the high-altitude site, and excellent receivers with low-noise performance provide an extremely sensitive, flexible instrument for submillimeter imaging.
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The present document outlines a roadmap for future developments that will significantly expand ALMAs capabilities and enable it to produce even more exciting science in the coming decades. The proposed developments are motivated by the groundbreaking
results achieved by ALMA during its first five years of operation. The roadmap described here is based on input on new scientific directions and technical feasibility of future developments from the ALMA Science Advisory Committee (ASAC), the community, and technical documents. The Working Group recommends that the top development priority, based on scientific merit and technical feasibility, is to broaden the receiver IF bandwidth by at least a factor two, and to upgrade the associated electronics and correlator. These developments will advance a wide range of scientific studies by significantly reducing the time required for blind redshift surveys, chemical spectral scans, and deep continuum surveys. In order of scientific priority, receiver upgrades are recommended for intermediate (200-425 GHz), low (< 200 GHz), and high (> 425 GHz) frequencies. The Working Group recommends that the receiver and throughput developments proceed as soon as fiscally and technically feasible. As a first step, a technical and scientific group should be formed to formalize the top-level requirements. A team of systems engineers should then be charged with flowing these requirements down to the subsystems to form a consistent new set of minimum requirements, which future development projects would have to meet. Given that upgrading the throughput will impact many ALMA subsystems, the Working Group recommends that a team within ALMA be charged with coordinating and monitoring these developments. (Abbreviated)
ALMA will sustain its transformational science through 2030 via an aggressive series of upgrades, for which an overview is provided.
(abridged) The Atacama Large Millimeter/submillimeter Array (ALMA) was the top-ranked priority for a new ground-based facility in the 2000 Canadian Long Range Plan. Ten years later, at the time of LRP2010, ALMA construction was well underway, with fi
rst science observations anticipated for 2011. In the past 8 years, ALMA has proved itself to be a high-impact, high-demand observatory, with record numbers of proposals submitted to the annual calls and large numbers of highly cited scientific papers across fields from protoplanetary disks to high-redshift galaxies and quasars. The LRP2010 ALMA white paper laid out 8 specific metrics that could be used to judge the success of Canadas participation in ALMA. Among these metrics were publications (number; impact), collaborations (international; multi-wavelength), and student training. To call out one particular metric, Canadians are making excellent use of ALMA in training graduate students and postdocs: as of June 2018, 12 of 23 Canadian first-author papers were led by a graduate student, and a further 4 papers were led by postdocs. All 8 metrics argue for Canadas involvement in ALMA over the past decade to be judged a success. The successful achievement of these wide-ranging goals argues strongly for Canadas continuing participation in ALMA over the next decade and beyond. Looking forward, our community needs to: (1) maintain Canadian access to ALMA and our competitiveness in using ALMA; (2) preserve full Canadian funding for our share of ALMA operations; (3) identify components of ALMA development in which Canada can play a significant role, including stimulating expertise in submillimetre instrumentation to capitalize on future opportunities; and (4) keep Canadians fully trained and engaged in ALMA, as new capabilities become available, reaching the widest possible community of potential users.
This white paper submitted for the 2020 Canadian Long-Range Planning process (LRP2020) presents the prospects for Canada and the Square Kilometre Array (SKA) from 2020-2030, focussing on the first phase of the project (SKA1) scheduled to begin constr
uction early in the next decade. SKA1 will make transformational advances in our understanding of the Universe across a wide range of fields, and Canadians are poised to play leadership roles in several. Canadian key SKA technologies will ensure a good return on capital investment in addition to strong scientific returns, positioning Canadian astronomy for future opportunities well beyond 2030. We therefore advocate for Canadas continued scientific and technological engagement in the SKA from 2020-2030 through participation in the construction and operations phases of SKA1.
ALMA has been operating since 2011, but has not yet been populated with the full suite of intended frequency bands. In particular, ALMA Band 2 (67-90 GHz) is the final band in the original ALMA band definition to be approved for production. We aim to
produce a wideband, tuneable, sideband-separating receiver with 28 GHz of instantaneous bandwidth per polarisation operating in the sky frequency range 67-116 GHz. Our design anticipates new ALMA requirements following the recommendations in the 2030 ALMA Development Roadmap. The cryogenic cartridge is designed to be compatible with the ALMA Band 2 cartridge slot, where the coldest components -- the feedhorns, orthomode transducers, and cryogenic low noise amplifiers -- operate at a temperature of 15 K. We use multiple simulation methods and tools to optimise our designs for both the passive optics and the active components. The cryogenic cartridge interfaces with a room temperature cartridge hosting the local oscillator (LO) and the downconverter module. This warm cartridge is largely based on GaAs semiconductor technology and is optimised to match the cryogenic receiver bandwidth with the required instantaneous LO tuning range. Our collaboration has designed, fabricated, and tested multiple technical solutions for each of the components, producing a state-of-the-art receiver covering the full ALMA Band 2 & 3 atmospheric window. The receiver is suitable for deployment on ALMA in the coming years, and is capable of dual-polarisation, sideband-separating observations in intermediate frequency bands spanning 4-18 GHz, for a total of 28 GHz on-sky bandwidth per polarisation channel. We conclude that the 67-116 GHz wideband implementation for ALMA Band 2 is now feasible, and this receiver is a compelling instrumental upgrade that will enhance observational capabilities and scientific reach.
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