Microwave SQUID multiplexing is a promising technique for multiplexing large arrays of transition edge sensors. A major bottleneck in the development and distribution of microwave SQUID multiplexer ...chips occurs in the time-intensive design testing and quality assurance stages. To obtain useful RF measurements, these devices must be cooled to temperatures below 500 mK. The need for a more efficient system to screen microwave multiplexer chips has grown as the number of chips requested by collaborators per year reaches into the hundreds. We have therefore assembled a test bed for microwave SQUID circuits, which decreases screening time for four 32-channel chips from 24 h in an adiabatic demagnetization refrigerator to approximately 5 h in a helium dip probe containing a closed cycle
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He sorption refrigerator. We discuss defining characteristics of these microwave circuits and the challenges of establishing an efficient testing setup for them.
MUSTANG-2 is a 90 GHz feedhorn-coupled, microwave SQUID-multiplexed TES bolometer array in the final stages of development for operation on the 100-m Robert C. Byrd Green Bank Telescope. We present ...the camera design and report the performance during the first season of observation, in which 64 of the available 215 pixels in the focal plane were populated. We highlight the microwave multiplexing readout technology, which is envisioned as a path to read out the next generation of large pixel-count cryogenic focal planes. In this regard, MUSTANG2 is a pathfinder for this multiplexing technology. We present noise spectra which show no detector noise degradation when read out with microwave SQUID multiplexing, and we present first light images of Jupiter and M87, which demonstrate the end-to-end system performance.
The stability of Al–Mn transition edge sensor (TES) bolometers is studied as we vary the engineered TES transition, heat capacity, and/or coupling between the heat capacity and TES. We present ...thermal structure measurements of each of the 39 designs tested. The data is accurately fit by a two-body bolometer model, which allows us to extract the basic TES parameters that affect device stability. We conclude that parameters affecting device stability can be engineered for optimal device operation, and present the model parameters extracted for the different TES designs.
Multi-chroic polarization sensitive detectors offer an avenue to increase both the spectral coverage and sensitivity of instruments optimized for observations of the cosmic-microwave background (CMB) ...or sub-mm sky. We report on an effort to adapt the Truce Collaboration horn coupled bolometric polarimeters for operation over octave bandwidth. Development is focused on detectors operating in both the 90 and 150 GHz bands which offer the highest CMB polarization to foreground ratio. We plan to deploy an array of 256 multi-chroic 90/150 GHz polarimeters with 1024 TES detectors on ACTPol in 2013, and there are proposals to use this technology for balloon-borne instruments. The combination of excellent control of beam systematics and sensitivity make this technology ideal for future ground, ballon, and space missions.
Dielectric loss in low-temperature superconducting integrated circuits can cause lower overall efficiency, particularly in the 90 to 220 GHz regime. We present a method to tune the dielectric loss ...for silicon oxide deposited by plasma-enhanced chemical-vapor deposition at ambient temperatures. Deposition in an environment with a higher silane-to-oxygen ratio produces silicon oxide films with a lower loss-tangent and a slightly higher optical index of refraction, while contributing no appreciable change in film stress. We measured the dielectric loss by fabricating a series of Nb-SiO x -Nb microstrip resonators in the frequency range of 6 to 9 GHz and comparing their temperature dependence to a model of parasitic two-level-system fluctuators. The dielectric loss-tangent of silicon oxide was improved from 6 ×10 -3 for stoichiometric silicon dioxide to 2 ×10 -3 for a more silicon-rich silicon oxide. We present details of the fabrication process and measurements of microstrip resonators.
We present a catalog of 4195 optically confirmed Sunyaev-Zel'dovich (SZ) selected galaxy clusters detected with signal-to-noise ratio >4 in 13,211 deg2 of sky surveyed by the Atacama Cosmology ...Telescope (ACT). Cluster candidates were selected by applying a multifrequency matched filter to 98 and 150 GHz maps constructed from ACT observations obtained from 2008 to 2018 and confirmed using deep, wide-area optical surveys. The clusters span the redshift range 0.04 < z < 1.91 (median z = 0.52). The catalog contains 222 z > 1 clusters, and a total of 868 systems are new discoveries. Assuming an SZ signal versus mass-scaling relation calibrated from X-ray observations, the sample has a 90% completeness mass limit of M500c > 3.8 × 1014 M , evaluated at z = 0.5, for clusters detected at signal-to-noise ratio >5 in maps filtered at an angular scale of 2 4. The survey has a large overlap with deep optical weak-lensing surveys that are being used to calibrate the SZ signal mass-scaling relation, such as the Dark Energy Survey (4566 deg2), the Hyper Suprime-Cam Subaru Strategic Program (469 deg2), and the Kilo Degree Survey (825 deg2). We highlight some noteworthy objects in the sample, including potentially projected systems, clusters with strong lensing features, clusters with active central galaxies or star formation, and systems of multiple clusters that may be physically associated. The cluster catalog will be a useful resource for future cosmological analyses and studying the evolution of the intracluster medium and galaxies in massive clusters over the past 10 Gyr.
We present the design for arrays of dual-polarization sensitive, superconducting sensors for far infrared astrophysics. Each pixel is feedhorn-coupled and consists of orthogonal, lumped-element ...kinetic inductance detectors (LEKIDs) both fabricated in the same deposition layer. Each LEKID pair contains an absorptive "one-turn" inductor and a large interdigitated capacitor (IDC) made of stoichiometric titanium nitride (TiN) with T c ~ 4.5 K. Crossovers between the two inductors are bridged with short sections of niobium. This design enables dual-polarization sensitivity at frequencies above the superconducting gap of niobium (>; 700 GHz). Simulations of the optical coupling show 83% co-polar and ≤ 0.3% cross-polar coupling averaged over a 400 GHz band centered on 1.2 THz. The intrapixel resonator cross-talk is <; 0.01%. Arrays of dual-polarization sensitive LEKIDs (or POLEKIDs) will be deployed on the balloon-borne instrument super-BLASTPol.
ACTPol is a polarization-sensitive receiver upgrade to the Atacama Cosmology Telescope (ACT) which will make millimeter wavelength measurements of the small-scale polarization anisotropies of the ...cosmic microwave background to investigate the properties of inflation, dark energy, dark matter, and neutrinos in the early Universe. ACTPol will employ three arrays of transition edge sensor (TES) bolometer detectors. The detectors, with a target transition temperature of 150 mK, will be operated at a bath temperature of 100 mK provided by a dilution refrigerator. One array operating at a central frequency of 150 GHz and consisting of 1024 TESes achieved first light at the ACT site in July 2013. We anticipate fielding the remainder of the focal plane, consisting of a second 150 GHz array and a multi-chroic array sensitive to 90 and 150 GHz, at the end of the 2013 observing season. In these proceedings, we present characterization of key detector parameters from measurements performed on the first array both in the lab and during initial field testing. We comment on the design goals, measurements, and uniformity of the detector transition temperatures, saturation powers, and thermal conductivities while detailing measurement methods and results for the detector optical efficiencies and time constants.
Our group at UC Berkeley has produced the next generation of millimeter-wave spiderweb-absorber transition edge sensor (TES) bolometer technology, which was originally developed for the Atacama ...Pathfinder Experiment—Sunyaev Zel’dolvich (APEX-SZ) and South Pole Telescope (SPT) experiments. We will discuss the adaptation of this technology to a balloon-borne environment and to sub-millimeter wavelengths for the E and B Experiment (EBEX) and the Atacama Sub-millimeter Telescope Experiment (ASTE). Specifically, this proceedings will address the methods we used to increase the thermal contact between the TES and a heat capacity used to limit electrothermal bandwidth, increase the optical efficiency at sub-millimeter wavelengths by reducing the grid spacing of the spiderweb absorber, and reduce the saturation power of the bolometers by a factor of 4 compared to the lowest saturation power SPT bolometers by the altering the bolometer geometry.
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