arXiv subjects

Nicholas F. Cothard

Publications and source records attributed to Nicholas F. Cothard.

45 records · Page 3Linked to original sources

arXiv2020

Sensitivity of the Prime-Cam Instrument on the CCAT-prime Telescope

CCAT-prime is a new 6 m crossed Dragone telescope designed to characterize the Cosmic Microwave Background (CMB) polarization and foregrounds, measure the Sunyaev-Zel'dovich effects of galaxy clusters, map the [CII] emission intensity from the Epoch of Reionization (EoR), and monitor accretion luminosity over multi-year timescales of hundreds of protostars in the Milky Way. CCAT-prime will make observations from a 5,600 m altitude site on Cerro Chajnantor in the Atacama Desert of northern Chile. The novel optical design of the telescope combined with high surface accuracy ($<$10 $μ$m) mirrors and the exceptional atmospheric conditions of the site will enable sensitive broadband, polarimetric, and spectroscopic surveys at sub-mm to mm wavelengths. Prime-Cam, the first light instrument for CCAT-prime, consists of a 1.8 m diameter cryostat that can house seven individual instrument modules. Each instrument module, optimized for a specific science goal, will use state-of-the-art kinetic inductance detector (KID) arrays operated at $\sim$100 mK, and Fabry-Perot interferometers (FPI) for the EoR science. Prime-Cam will be commissioned with staged deployments to populate the seven instrument modules. The full instrument will consist of 60,000 polarimetric KIDs at a combination of 220/280/350/410 GHz, 31,000 KIDS at 250/360 GHz coupled with FPIs, and 21,000 polarimetric KIDs at 850 GHz. Prime-Cam is currently being built, and the CCAT-prime telescope is designed and under construction by Vertex Antennentechnik GmbH to achieve first light in 2021. CCAT-prime is also a potential telescope platform for the future CMB Stage-IV observations.

astro-ph.IM↗

arXiv2020

Characterization of Transition Edge Sensors for the Simons Observatory

The Simons Observatory is building both large (6 m) and small (0.5 m) aperture telescopes in the Atacama desert in Chile to observe the cosmic microwave background (CMB) radiation with unprecedented sensitivity. Simons Observatory telescopes in total will use over 60,000 transition edge sensor (TES) detectors spanning center frequencies between 27 and 285 GHz and operating near 100 mK. TES devices have been fabricated for the Simons Observatory by NIST, Berkeley, and HYPRES/SeeQC corporation. Iterations of these devices have been tested cryogenically in order to inform the fabrication of further devices, which will culminate in the final TES designs to be deployed in the field. The detailed design specifications have been independently iterated at each fabrication facility for particular detector frequencies. We present test results for prototype devices, with emphasis on NIST high frequency detectors. A dilution refrigerator was used to achieve the required temperatures. Measurements were made both with 4-lead resistance measurements and with a time domain Superconducting Quantum Interference Device (SQUID) multiplexer system. The SQUID readout measurements include analysis of current vs voltage (IV) curves at various temperatures, square wave bias step measurements, and detector noise measurements. Normal resistance, superconducting critical temperature, saturation power, thermal and natural time constants, and thermal properties of the devices are extracted from these measurements.

astro-ph.IM↗

arXiv2019

The Simons Observatory: Astro2020 Decadal Project Whitepaper

The Simons Observatory (SO) is a ground-based cosmic microwave background (CMB) experiment sited on Cerro Toco in the Atacama Desert in Chile that promises to provide breakthrough discoveries in fundamental physics, cosmology, and astrophysics. Supported by the Simons Foundation, the Heising-Simons Foundation, and with contributions from collaborating institutions, SO will see first light in 2021 and start a five year survey in 2022. SO has 287 collaborators from 12 countries and 53 institutions, including 85 students and 90 postdocs. The SO experiment in its currently funded form ('SO-Nominal') consists of three 0.4 m Small Aperture Telescopes (SATs) and one 6 m Large Aperture Telescope (LAT). Optimized for minimizing systematic errors in polarization measurements at large angular scales, the SATs will perform a deep, degree-scale survey of 10% of the sky to search for the signature of primordial gravitational waves. The LAT will survey 40% of the sky with arc-minute resolution. These observations will measure (or limit) the sum of neutrino masses, search for light relics, measure the early behavior of Dark Energy, and refine our understanding of the intergalactic medium, clusters and the role of feedback in galaxy formation. With up to ten times the sensitivity and five times the angular resolution of the Planck satellite, and roughly an order of magnitude increase in mapping speed over currently operating ("Stage 3") experiments, SO will measure the CMB temperature and polarization fluctuations to exquisite precision in six frequency bands from 27 to 280 GHz. SO will rapidly advance CMB science while informing the design of future observatories such as CMB-S4.

astro-ph.IM↗

arXiv2019

The Simons Observatory: Science goals and forecasts

The Simons Observatory (SO) is a new cosmic microwave background experiment being built on Cerro Toco in Chile, due to begin observations in the early 2020s. We describe the scientific goals of the experiment, motivate the design, and forecast its performance. SO will measure the temperature and polarization anisotropy of the cosmic microwave background in six frequency bands: 27, 39, 93, 145, 225 and 280 GHz. The initial configuration of SO will have three small-aperture 0.5-m telescopes (SATs) and one large-aperture 6-m telescope (LAT), with a total of 60,000 cryogenic bolometers. Our key science goals are to characterize the primordial perturbations, measure the number of relativistic species and the mass of neutrinos, test for deviations from a cosmological constant, improve our understanding of galaxy evolution, and constrain the duration of reionization. The SATs will target the largest angular scales observable from Chile, mapping ~10% of the sky to a white noise level of 2 $μ$K-arcmin in combined 93 and 145 GHz bands, to measure the primordial tensor-to-scalar ratio, $r$, at a target level of $σ(r)=0.003$. The LAT will map ~40% of the sky at arcminute angular resolution to an expected white noise level of 6 $μ$K-arcmin in combined 93 and 145 GHz bands, overlapping with the majority of the LSST sky region and partially with DESI. With up to an order of magnitude lower polarization noise than maps from the Planck satellite, the high-resolution sky maps will constrain cosmological parameters derived from the damping tail, gravitational lensing of the microwave background, the primordial bispectrum, and the thermal and kinematic Sunyaev-Zel'dovich effects, and will aid in delensing the large-angle polarization signal to measure the tensor-to-scalar ratio. The survey will also provide a legacy catalog of 16,000 galaxy clusters and more than 20,000 extragalactic sources.

astro-ph.CO↗

arXiv2018

Far Sidelobes from Baffles and Telescope Support Structures in the Atacama Cosmology Telescope

The Atacama Cosmology Telescope (ACT) is a 6 m telescope located in the Atacama Desert, designed to measure the cosmic microwave background (CMB) with arcminute resolution. ACT, with its third generation polarization sensitive array, Advanced ACTPol, is being used to measure the anisotropies of the CMB in five frequency bands in large areas of the sky ($\sim 15,000$ $\rm deg^2$). These measurements are designed to characterize the large scale structure of the universe, test cosmological models and constrain the sum of the neutrino masses. As the sensitivity of these wide surveys increases, the control and validation of the far sidelobe response becomes increasingly important and is particularly challenging as multiple reflections, spillover, diffraction and scattering become difficult to model and characterize at the required levels. In this work, we present a ray trace model of the ACT upper structure which is used to describe much of the observed far sidelobe pattern. This model combines secondary mirror spillover measurements with a 3D CAD model based on photogrammetry measurements to simulate the beam of the camera and the comoving ground shield. This simulation shows qualitative agreement with physical optics tools and features observed in far sidelobe measurements. We present this method as an efficient first-order calculation that, although it does not capture all diffraction effects, informs interactions between the structural components of the telescope and the optical path, which can then be combined with more computationally intensive physical optics calculations. This method can be used to predict sidelobe patterns in the design stage of future optical systems such as the Simons Observatory, CCAT-prime, and CMB Stage IV.

astro-ph.IM↗

arXiv2018

Optimizing the Efficiency of Fabry-Perot Interferometers with Silicon-Substrate Mirrors

We present the novel design of microfabricated, silicon-substrate based mirrors for use in cryogenic Fabry-Perot Interferometers (FPIs) for the mid-IR to sub-mm/mm wavelength regime. One side of the silicon substrate will have a double-layer metamaterial anti-reflection coating (ARC) anisotropically etched into it and the other side will be metalized with a reflective mesh pattern. The double-layer ARC ensures a reflectance of less than 1% at the surface substrate over the FPI bandwidth. This low reflectance is required to achieve broadband capability and to mitigate contaminating resonances from the silicon surface. Two silicon substrates with their metalized surfaces facing each other and held parallel with an adjustable separation will compose the FPI. To create an FPI with nearly uniform finesse over the FPI bandwidth, we use a combination of inductive and capacitive gold meshes evaporated onto the silicon substrate. We also consider the use of niobium as a superconducting reflective mesh for long wavelengths to eliminate ohmic losses at each reflection in the resonating cavity of the FPI and thereby increase overall transmission. We develop these silicon-substrate based FPIs for use in ground (e.g. CCAT-prime), air (e.g. HIRMES), and future space-based telescopes (e.g. the Origins Space Telescope concept). Such FPIs are well suited for spectroscopic imaging with the upcoming large IR/sub-mm/mm TES bolometer detector arrays. Here we present the fabrication and performance of multi-layer, plasma-etched, silicon metamaterial ARC, as well as models of the mirrors and FPIs.

astro-ph.IM↗

arXiv2018

Prime-Cam: A first-light instrument for the CCAT-prime telescope

CCAT-prime will be a 6-meter aperture telescope operating from sub-mm to mm wavelengths, located at 5600 meters elevation on Cerro Chajnantor in the Atacama Desert in Chile. Its novel crossed-Dragone optical design will deliver a high throughput, wide field of view capable of illuminating much larger arrays of sub-mm and mm detectors than can existing telescopes. We present an overview of the motivation and design of Prime-Cam, a first-light instrument for CCAT-prime. Prime-Cam will house seven instrument modules in a 1.8 meter diameter cryostat, cooled by a dilution refrigerator. The optical elements will consist of silicon lenses, and the instrument modules can be individually optimized for particular science goals. The current design enables both broadband, dual-polarization measurements and narrow-band, Fabry-Perot spectroscopic imaging using multichroic transition-edge sensor (TES) bolometers operating between 190 and 450 GHz. It also includes broadband kinetic induction detectors (KIDs) operating at 860 GHz. This wide range of frequencies will allow excellent characterization and removal of galactic foregrounds, which will enable precision measurements of the sub-mm and mm sky. Prime-Cam will be used to constrain cosmology via the Sunyaev-Zeldovich effects, map the intensity of [CII] 158 $μ$m emission from the Epoch of Reionization, measure Cosmic Microwave Background polarization and foregrounds, and characterize the star formation history over a wide range of redshifts. More information about CCAT-prime can be found at www.ccatobservatory.org.

astro-ph.IM↗

arXiv2018

Advanced ACTPol Low Frequency Array: Readout and Characterization of Prototype 27 and 39 GHz Transition Edge Sensors

Advanced ACTPol (AdvACT) is a third generation polarization upgrade to the Atacama Cosmology Telescope, designed to observe the cosmic microwave background (CMB). AdvACT expands on the 90 and 150 GHz transition edge sensor (TES) bolometer arrays of the ACT Polarimeter (ACTPol), adding both high frequency (HF, 150/230 GHz) and low frequency (LF, 27/39 GHz) multichroic arrays. The addition of the high and low frequency detectors allows for the characterization of synchrotron and spinning dust emission at the low frequencies and foreground emission from galactic dust and dusty star forming galaxies at the high frequencies. The increased spectral coverage of AdvACT will enable a wide range of CMB science, such as improving constraints on dark energy, the sum of the neutrino masses, and the existence of primordial gravitational waves. The LF array will be the final AdvACT array, replacing one of the MF arrays for a single season. Prior to the fabrication of the final LF detector array, we designed and characterized prototype TES bolometers. Detector geometries in these prototypes are varied in order to inform and optimize the bolometer designs for the LF array, which requires significantly lower noise levels and saturation powers (as low as ${\sim}1$ pW) than the higher frequency detectors. Here we present results from tests of the first LF prototype TES detectors for AdvACT, including measurements of the saturation power, critical temperature, thermal conductance and time constants. We also describe the modifications to the time-division SQUID readout architecture compared to the MF and HF arrays.

astro-ph.IM↗

arXiv2016

Readout of two-kilopixel transition-edge sensor arrays for Advanced ACTPol

Advanced ACTPol is an instrument upgrade for the six-meter Atacama Cosmology Telescope (ACT) designed to measure the cosmic microwave background (CMB) temperature and polarization with arcminute-scale angular resolution. To achieve its science goals, Advanced ACTPol utilizes a larger readout multiplexing factor than any previous CMB experiment to measure detector arrays with approximately two thousand transition-edge sensor (TES) bolometers in each 150 mm detector wafer. We present the implementation and testing of the Advanced ACTPol time-division multiplexing readout architecture with a 64-row multiplexing factor. This includes testing of individual multichroic detector pixels and superconducting quantum interference device (SQUID) multiplexing chips as well as testing and optimizing of the integrated readout electronics. In particular, we describe the new automated multiplexing SQUID tuning procedure developed to select and optimize the thousands of SQUID parameters required to readout each Advanced ACTPol array. The multichroic detector pixels in each array use separate channels for each polarization and each of the two frequencies, such that four TESes must be read out per pixel. Challenges addressed include doubling the number of detectors per multiplexed readout channel compared to ACTPol and optimizing the Nyquist inductance to minimize detector and SQUID noise aliasing.

astro-ph.IM↗