ALMA SIS mixer optimization for stable operation

ABSTRACT The Atacama Large Millimeter/Submillimeter Array (ALMA), an interferometric radio telescope will have 66 array elements when complete. The ALMA Front End is designed to accommodate up to 10 receiver bands covering most of the wavelength range from 10 to 0.3 mm. Superconductor-insulator-superconductor (SIS) mixers are employed for Bands 3 (~3 mm) through 10 (~0.3 mm). Ordinarily the SIS bias is selected to achieve the lowest receiver noise temperatures. However, in order to obtain the lowest detection threshold, the SIS bias also needs to be optimized with respect to receiver stability. There are also other parameters to be optimized such as the magnetic field strength used to suppress the Josephson currents and avoidance of Shapiro. This paper will summarize the results of work carried out to derive the optimal operating parameters for the large number of mixers in use on the telescope so as to keep the telescope operating reliably and repeatably

First analysis of solar structures in 1.21 mm full-disc ALMA image of the Sun

Various solar features can be seen on maps of the Sun in the mm and sub-mm wavelength range. The recently installed Atacama Large Millimeter/submillimeter Array (ALMA) is capable of observing the Sun in that wavelength range with an unprecedented spatial, temporal and spectral resolution. To interpret solar observations with ALMA the first important step is to compare ALMA maps with simultaneous images of the Sun recorded in other spectral ranges. First we identify different structures in the solar atmosphere seen in the optical, IR and EUV parts of the spectrum (quiet Sun (QS), active regions (AR), prominences on the disc, magnetic inversion lines (IL), coronal holes (CH) and coronal bright points (CBPs)) in a full disc solar ALMA image. The second aim is to measure the intensities (brightness temperatures) of those structures and compare them with the corresponding QS level. A full disc solar image at 1.21 mm obtained on December 18, 2015 during a CSV-EOC campaign with ALMA is calibrated and compared with full disc solar images from the same day in H\alpha, in He I 1083 nm core, and with SDO images (AIA at 170 nm, 30.4 nm, 21.1 nm, 19.3 nm, and 17.1 nm and HMI magnetogram). The brightness temperatures of various structures are determined by averaging over corresponding regions of interest in the ALMA image. Positions of the QS, ARs, prominences on the disc, ILs, CHs and CBPs are identified in the ALMA image. At 1.21 mm ARs appear as bright areas (but sunspots are dark), while prominences on the disc and CHs are not discernible from the QS background, although having slightly less intensity than surrounding QS regions. ILs appear as large, elongated dark structures and CBPs correspond to ALMA bright points. These results are in general agreement with sparse earlier measurements at similar wavelengths. The identification of CBPs represents the most important new result.Comment: 9 pages, 3 figure

Solar science with the Atacama Large Millimeter/submillimeter Array - A new view of our Sun

The Atacama Large Millimeter/submillimeter Array (ALMA) is a new powerful tool for observing the Sun at high spatial, temporal, and spectral resolution. These capabilities can address a broad range of fundamental scientific questions in solar physics. The radiation observed by ALMA originates mostly from the chromosphere - a complex and dynamic region between the photosphere and corona, which plays a crucial role in the transport of energy and matter and, ultimately, the heating of the outer layers of the solar atmosphere. Based on first solar test observations, strategies for regular solar campaigns are currently being developed. State-of-the-art numerical simulations of the solar atmosphere and modeling of instrumental effects can help constrain and optimize future observing modes for ALMA. Here we present a short technical description of ALMA and an overview of past efforts and future possibilities for solar observations at submillimeter and millimeter wavelengths. In addition, selected numerical simulations and observations at other wavelengths demonstrate ALMA's scientific potential for studying the Sun for a large range of science cases.Comment: 73 pages, 21 figures ; Space Science Reviews (accepted December 10th, 2015); accepted versio

Observing the Sun with Atacama Large Millimeter/submillimeter Array (ALMA): High Resolution Interferometric Imaging

Observations of the Sun at millimeter and submillimeter wavelengths offer a unique probe into the structure, dynamics, and heating of the chromosphere; the structure of sunspots; the formation and eruption of prominences and filaments; and energetic phenomena such as jets and flares. High-resolution observations of the Sun at millimeter and submillimeter wavelengths are challenging due to the intense, extended, low- contrast, and dynamic nature of emission from the quiet Sun, and the extremely intense and variable nature of emissions associated with energetic phenomena. The Atacama Large Millimeter/submillimeter Array (ALMA) was designed with solar observations in mind. The requirements for solar observations are significantly different from observations of sidereal sources and special measures are necessary to successfully carry out this type of observations. We describe the commissioning efforts that enable the use of two frequency bands, the 3 mm band (Band 3) and the 1.25 mm band (Band 6), for continuum interferometric-imaging observations of the Sun with ALMA. Examples of high-resolution synthesized images obtained using the newly commissioned modes during the solar commissioning campaign held in December 2015 are presented. Although only 30 of the eventual 66 ALMA antennas were used for the campaign, the solar images synthesized from the ALMA commissioning data reveal new features of the solar atmosphere that demonstrate the potential power of ALMA solar observations. The ongoing expansion of ALMA and solar-commissioning efforts will continue to enable new and unique solar observing capabilities.Comment: 22 pages, 12 figures, accepted for publication in Solar Physic

An ultra-broadband optical system for ALMA Band 2+3

ALMA is the largest radio astronomical facility in the world providing high sensitivity between 35 and 950 GHz, divided in 10 bands with fractional bandwidths between 19 and 36%. Having a lifespan of at least 30 years, ALMA carries out a permanent upgrading plan which, for the receivers, is focused on achieving better sensitivity and larger bandwidths. As result, an international consortium works on demonstrating a prototype receiver covering currents Bands 2 and 3 (67 to 116 GHz) which corresponds to a fractional bandwidth of 54%. Here we present the preliminary design, implementation and characterization of suitable refractive optics. Results indicate an excellent performance in good agreement with simulations

Observing the Sun with the Atacama Large Millimeter-submillimeter Array (ALMA): Fast-Scan Single-Dish Mapping

The Atacama Large Millimeter-submillimeter Array (ALMA) radio telescope has commenced science observations of the Sun starting in late 2016. Since the Sun is much larger than the field of view of individual ALMA dishes, the ALMA interferometer is unable to measure the background level of solar emission when observing the solar disk. The absolute temperature scale is a critical measurement for much of ALMA solar science, including the understanding of energy transfer through the solar atmosphere, the properties of prominences, and the study of shock heating in the chromosphere. In order to provide an absolute temperature scale, ALMA solar observing will take advantage of the remarkable fast-scanning capabilities of the ALMA 12m dishes to make single-dish maps of the full Sun. This article reports on the results of an extensive commissioning effort to optimize the mapping procedure, and it describes the nature of the resulting data. Amplitude calibration is discussed in detail: a path that utilizes the two loads in the ALMA calibration system as well as sky measurements is described and applied to commissioning data. Inspection of a large number of single-dish datasets shows significant variation in the resulting temperatures, and based on the temperature distributions we derive quiet-Sun values at disk center of 7300 K at lambda=3 mm and 5900 K at lambda=1.3 mm. These values have statistical uncertainties of order 100 K, but systematic uncertainties in the temperature scale that may be significantly larger. Example images are presented from two periods with very different levels of solar activity. At a resolution of order 25 arcsec, the 1.3 mm wavelength images show temperatures on the disk that vary over about a 2000 K range.Comment: Solar Physics, accepted: 24 pages, 13 figure

Wideband 67-116 GHz cryogenic receiver development for ALMA Band 2

The Atacama Large Millimeter/sub-millimeter Array (ALMA) is already revolutionising our understanding of the Universe. However, ALMA is not yet equipped with all of its originally planned receiver bands, which will allow it to observe over the full range of frequencies from 35-950 GHz accessible through the Earth's atmosphere. In particular Band 2 (67-90 GHz) has not yet been approved for construction. Recent technological developments in cryogenic monolithic microwave integrated circuit (MMIC) high electron mobility transistor (HEMT) amplifier and orthomode transducer (OMT) design provide an opportunity to extend the originally planned on-sky bandwidth, combining ALMA Bands 2 and 3 into one receiver cartridge covering 67-116 GHz. The IF band definition for the ALMA project took place two decades ago, when 8 GHz of on-sky bandwidth per polarisation channel was an ambitious goal. The new receiver design we present here allows the opportunity to expand ALMA's wideband capabilities, anticipating future upgrades across the entire observatory. Expanding ALMA's instantaneous bandwidth is a high priority, and provides a number of observational advantages, including lower noise in continuum observations, the ability to probe larger portions of an astronomical spectrum for, e.g., widely spaced molecular transitions, and the ability to scan efficiently in frequency space to perform surveys where the redshift or chemical complexity of the object is not known a priori. Wider IF bandwidth also reduces uncertainties in calibration and continuum subtraction that might otherwise compromise science objectives. Here we provide an overview of the component development and overall design for this wideband 67-116 GHz cryogenic receiver cartridge, designed to operate from the Band 2 receiver cartridge slot in the current ALMA front end receiver cryostat.Comment: 8 pages, proceedings from the 8th ESA Workshop on Millimetre-Wave Technology and Applications (https://atpi.eventsair.com/QuickEventWebsitePortal/millimetre-wave/mm-wave

ALMA band 2+3 (67-116 GHz) optics: Design and first measurements

The ALMA telescope is one of the largest on-ground astronomical projects in the world. It has been producing great scientific results since the beginning of operations in 2011. Of all the originally planned bands, band 2 (67-90 GHz) is the last band to be implemented into the array. Recent technological progress has open the possibility to combine bands 2 and 3 (84-116 GHz) into a single wideband receiver. This paper describes the first efforts to design wideband optics which cover both bands, from 67 to 116 GHz, using a profiled corrugated horn and a modified Fresnel lens. First measurements were performed at ESO in Dec15-Jan16 and showed good agreement with simulations

ALMA Observations of the Sun in Cycle 4 and Beyond

This document was created by the Solar Simulations for the Atacama Large Millimeter Observatory Network (SSALMON) in preparation of the first regular observations of the Sun with the Atacama Large Millimeter/submillimeter Array (ALMA), which are anticipated to start in ALMA Cycle 4 in October 2016. The science cases presented here demonstrate that a large number of scientifically highly interesting observations could be made already with the still limited solar observing modes foreseen for Cycle 4 and that ALMA has the potential to make important contributions to answering long-standing scientific questions in solar physics. With the proposal deadline for ALMA Cycle 4 in April 2016 and the Commissioning and Science Verification campaign in December 2015 in sight, several of the SSALMON Expert Teams composed strategic documents in which they outlined potential solar observations that could be feasible given the anticipated technical capabilities in Cycle 4. These documents have been combined and supplemented with an analysis, resulting in recommendations for solar observing with ALMA in Cycle 4. In addition, the detailed science cases also demonstrate the scientific priorities of the solar physics community and which capabilities are wanted for the next observing cycles. The work on this White Paper effort was coordinated in close cooperation with the two international solar ALMA development studies led by T. Bastian (NRAO, USA) and R. Brajsa, (ESO). This document will be further updated until the beginning of Cycle 4 in October 2016. In particular, we plan to adjust the technical capabilities of the solar observing modes once finally decided and to further demonstrate the feasibility and scientific potential of the included science cases by means of numerical simulations of the solar atmosphere and corresponding simulated ALMA observations.Comment: SSALMON White Paper with focus on potential solar science with ALMA in Cycle 4; 54 pages. Version 1.2, March 29th, 2016 (updated technical capabilities and observing plans

Superconducting Submm Integrated Receiver for TELIS

In this report we present design and first experimental results for development of the submm superconducting integrated receiver spectrometer for Terahertz Limb Sounder (TELIS). TELIS is a collaborative European project to build up a three-channel heterodyne balloon-based spectrometer for measuring a variety of atmospheric constituents of the stratosphere. The 550 - 650 GHz channel of TELIS is based on a phase-locked Superconducting Integrated Receiver (SIR). SIR is an on-chip combination of a low-noise Superconductor-Insulator-Superconductor (SIS) mixer with quasioptical antenna, a superconducting Flux Flow Oscillator (FFO) acting as Local Oscillator (LO), and SIS harmonic mixer (HM) for FFO phase locking. A number of new solutions were implemented in the new generation of SIR chips. To achieve the wide-band performance of the spectrometer, a side-feed twin-SIS mixer and balanced SIS mixer with 0.8 µm2 junctions integrated with a double-dipole (or double-slot) antenna is used. An improved design of the FFO for TELIS has been developed and optimized providing a free-running linewidth between 10 and 2 MHz in the frequency range 500 - 700 GHz. It is important to ensure that tuning of a phase-locked (PL) SIR can be performed remotely by telecommand. For this purpose a number of approaches for the PL SIR automatic computer control have been developed. All receiver components (including input optical elements and Martin-Puplett polarization rotating interferometer for single side band operation) will be mounted on a single 4.2 K plate inside a 40 × 180 × 80 mm3 box. First measurements give an uncorrected double side band (DSB) noise temperature below 250 K measured with the phase-locked FFO; more detailed results are presented at the conference