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Nicholas F Cothard

Publications and source records attributed to Nicholas F Cothard.

6 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2021

The Simons Observatory Microwave SQUID Multiplexing Detector Module Design

Advances in cosmic microwave background(CMB)science depend on increasing the number of sensitive detectorsobserving the sky. New instruments deploy large arrays of superconducting transition-edge sensor(TES)bolometers tileddensely into ever larger focal planes. High multiplexing factors reduce the thermal loading on the cryogenic receivers andsimplify their design. We present the design of focal-plane modules with an order of magnitude higher multiplexingfactor than has previously been achieved with TES bolometers. We focus on the novel cold readout component, whichemploys microwave SQUID multiplexing(μmux). Simons Observatory will use 49 modules containing 70,000bolometers to make exquisitely sensitive measurements of the CMB. We validate the focal-plane module design,presenting measurements of the readout component with and without a prototype detector array of 1728 polarization-sensitive bolometers coupled to feedhorns. The readout component achieves a 95% yield and a 910 multiplexing factor.The median white noise of each readout channel is 65pA Hz. This impacts the projected SO mapping speed by<8%,which is less than is assumed in the sensitivity projections. The results validate the full functionality of the module. Wediscuss the measured performance in the context of SO science requirements, which are exceeded.

Heather McCarrick↗
NASA NTRS2021

Simons Observatory HoloSim-ML: Machine Learning Applied to the Efficient Analysis of Radio Holography Measurements of Complex Optical Systems

Near-field radio holography is a common method for measuring and aligning mirror surfaces for millimeter andsub-millimeter telescopes. In instruments with more than a single mirror, degeneracies arise in the holographymeasurement, requiring multiple measurements and new fitting methods. We present HoloSim-ML, a Pythoncode for beam simulation and analysis of radio holography data from complex optical systems. This code usesmachine learning to efficiently determine the position of hundreds of mirror adjusters on multiple mirrors with fewmicrometer accuracy. We apply this approach to the example of the Simons Observatory 6 m telescope.

Grace E Chesmore↗
NASA NTRS2021

Atacama Cosmology Telescope: Detection of Millimeter-Wave Transient Sources

We report on the serendipitous discovery of three transient millimeter-wave sources using data from the Atacama Cosmology Telescope. The first, detected at R.A. = 273.8138, decl. = −49.4628 at ∼50σ total, brightened from less than 5 mJy to at least 1100 mJy at 150 GHz with an unknown rise time shorter than 13 days, during which the increase from 250 mJy to 1100 mJy took only 8 minutes. Maximum flux was observed on 2019 November 8. The source's spectral index in flux between 90–150 GHz was positive, α = 1.5 ± 0.2. The second, detected at R.A. = 105.1584, decl. = −11.2434 at ∼20σ total, brightened from less than 20 mJy to at least 300 mJy at 150 GHz with an unknown rise time shorter than 8 days. Maximum flux was observed on 2019 December 15. Its spectral index was also positive, α = 1.8 ± 0.2. The third, detected at R.A. = 301.9952, decl. = 16.1652 at ∼40σ total, brightened from less than 8 mJy to at least 300 mJy at 150 GHz over a day or less but decayed over a few days. Maximum flux was observed on 2018 September 11. Its spectrum was approximately flat, with a spectral index of α = −0.2 ± 0.1. None of the sources were polarized to the limits of these measurements. The two rising-spectrum sources are coincident in position with M and K stars, while the third is coincident with a G star.

Time domain astronomy↗
NASA NTRS2021

In Situ Performance of the Low Frequency Array for Advanced ACTPol

The Advanced Atacama Cosmology Telescope Polarimeter (AdvACT) is an upgrade for the Atacama Cosmology Telescope using Transition Edge Sensor (TES) detector arrays to measure cosmic microwave background (CMB) temperature and polarization anisotropies in multiple frequencies. The low frequency (LF) array was deployed early 2020. It consists of 292 TES bolometers observing in two bands centered at 27 GHz and 39 GHz. At these frequencies, it is sensitive to synchrotron radiation from our galaxy as well as to the CMB, and complements the AdvACT arrays operating at 90, 150 and 230 GHz. We present the initial LF array on-site characterization, including the time constant, optical efficiency and array sensitivity.

Superconducting detectors↗