Search

The Simons Observatory (SO) is an upcoming polarization-sensitive Cosmic Microwave Background (CMB) experiment on the Cerro Toco Plateau (Chile) with large overlap with other optical and infrared surveys (e.g., DESI, LSST, HSC). To enable the readout of \bigO(10,000) detectors in each of the four telescopes of SO, we will employ the microwave SQUID multiplexing technology. With a targeted multiplexing factor of \bigO{(1,000)}, microwave SQUID multiplexing has never been deployed on the scale needed for SO. Here we present the design of the cryogenic coaxial cable and RF component chain that connects room temperature readout electronics to superconducting resonators that are coupled to Transition Edge Sensor bolometers operating at sub-Kelvin temperatures. We describe design considerations including cryogenic RF component selection, system linearity, noise, and thermal power dissipation., 10 pages, 2 figures

The Simons Observatory will measure the cosmic microwave background temperature and polarization using a suite of new telescopes in the Atacama Desert in Chile. The Simons Observatory will use dichroic transition edge sensor (TES) bolometer arrays spanning six frequency bands from 27 to 280 GHz. The Simons Observatory will pioneer the use of a densely packed multiplexing architecture based on the microwave SQUID multiplexer ($$\mu $$mux), housing $$\sim \! 2000$$ microwave resonators, each coupled to a TES. The Simons Observatory aims to multiplex each array of $$\sim \! 2000$$ detectors with a single pair of coaxial cables and requires a multiplexing factor of $$\sim \! 1000$$. The Simons Observatory cryogenic readout system is called the universal microwave multiplexing module (UMM). The UMM couples to both horn and lenslet-coupled detector arrays and is integrated into the universal focal-plane module (UFM) after being independently characterized. We present processes we have developed for highly repeatable and automated integration methods of UMMs, which will be needed for the production of the 49 UFMs required for the first stage of the Simons Observatory.

We describe the design and measurement of feedhorn-coupled, transition-edge sensor (TES) polarimeters with two passbands centered at 220 GHz and 280 GHz, intended for observations of the cosmic microwave background. Each pixel couples polarized light in two linear polarizations by use of a planar orthomode transducer and senses power via four TES bolometers, one for each band in each linear polarization. Previous designs of this detector architecture incorporated passbands from 27 GHz to 220 GHz; we now demonstrate this technology at frequencies up to 315 GHz. Observational passbands are defined with an on-chip diplexer, and Fourier-transform-spectrometer measurements are in excellent agreement with simulations. We find coupling from feedhorn to TES bolometer using a cryogenic, temperature-controlled thermal source. We determine the optical efficiency of our device is $\eta$ = 77%$\pm$6% (75%$\pm$5%) for 220 (280) GHz, relative to the designed passband shapes. Lastly, we compare two power-termination schemes commonly used in wide-bandwidth millimeter-wave polarimeters and find equal performance in terms of optical efficiency and passband shape., Comment: Proceedings for the 18th International Workshop on Low Temperature Detectors (LTD18), submitted to the Journal of Low Temperature Physics

Two recent large data releases for the Atacama Cosmology Telescope (ACT), called DR4 and DR5, are available for public access. These data include temperature and polarization maps that cover nearly half the sky at arcminute resolution in three frequency bands; lensing maps and component-separated maps covering ~ 2,100 deg^2 of sky; derived power spectra and cosmological likelihoods; a catalog of over 4,000 galaxy clusters; and supporting ancillary products including beam functions and masks. The data and products are described in a suite of ACT papers; here we provide a summary. In order to facilitate ease of access to these data we present a set of Jupyter IPython notebooks developed to introduce users to DR4, DR5, and the tools needed to analyze these data. The data products (excluding simulations) and the set of notebooks are publicly available on the NASA Legacy Archive for Microwave Background Data Analysis (LAMBDA); simulation products are available on the National Energy Research Scientific Computing Center (NERSC)., Accepted to ApJS. 21 pages, 8 figures. Data and notebooks available on LAMBDA https://lambda.gsfc.nasa.gov/product/act/

We present geometrical and physical optics simulation results for the Simons Observatory Large Aperture Telescope. This work was developed as part of the general design process for the telescope; allowing us to evaluate the impact of various design choices on performance metrics and potential systematic effects. The primary goal of the simulations was to evaluate the final design of the reflectors and the cold optics which are now being built. We describe non-sequential ray tracing used to inform the design of the cold optics, including absorbers internal to each optics tube. We discuss ray tracing simulations of the telescope structure that allow us to determine geometries that minimize detector loading and mitigate spurious near-field effects that have not been resolved by the internal baffling. We also describe physical optics simulations, performed over a range of frequencies and field locations, that produce estimates of monochromatic far field beam patterns which in turn are used to gauge general optical performance. Finally, we describe simulations that shed light on beam sidelobes from panel gap diffraction., 15 pages, 13 figures

The Advanced Atacama Cosmology Telescope Polarimeter (AdvACT) \cite{thornton} 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.

The CCAT-prime project's first light array will be deployed in Mod-Cam, a single-module testbed and first light cryostat, on the Fred Young Submillimeter Telescope (FYST) in Chile's high Atacama desert in late 2022. FYST is a six-meter aperture telescope being built on Cerro Chajnantor at an elevation of 5600 meters to observe at millimeter and submillimeter wavelengths.1 Mod-Cam will pave the way for Prime-Cam, the primary first generation instrument, which will house up to seven instrument modules to simultaneously observe the sky and study a diverse set of science goals from monitoring protostars to probing distant galaxy clusters and characterizing the cosmic microwave background (CMB). At least one feedhorn-coupled array of microwave kinetic inductance detectors (MKIDs) centered on 280 GHz will be included in Mod-Cam at first light, with additional instrument modules to be deployed along with Prime-Cam in stages. The first 280 GHz detector array was fabricated by the Quantum Sensors Group at NIST in Boulder, CO and includes 3,456 polarization-sensitive MKIDs. Current mechanical designs allow for up to three hexagonal arrays to be placed in each single instrument module. We present details on this first light detector array, including mechanical designs and cold readout plans, as well as introducing Mod-Cam as both a testbed and predecessor to Prime-Cam., Comment: 9 pages, 6 figures, SPIE Astronomical Telescopes + Instrumentation 2020, Paper Number: 11453-58

TolTEC is a 3-band millimeter-wave imaging polarimeter scheduled for deployment to the Large Millimeter Telescope (LMT) in January 2020. TolTEC consists of three, kilopixel-scale, monolithic arrays of microwave kinetic inductance detectors (MKIDs), together comprising over 7,000 polarization sensitive detectors. Here we describe many of the unique aspects of the TolTEC all-silicon focal plane design. We then present both laboratory and fully integrated in-receiver measurements in the lab with which we characterize the optical, resonator, and noise properties of the arrays.

TolTEC is a three-band imaging polarimeter for the Large Millimeter Telescope. Simultaneously observing with passbands at 1.1mm, 1.4mm and 2.0mm, TolTEC has diffraction-limited beams with FWHM of 5, 7, and 11 arcsec, respectively. Over the coming decade, TolTEC will perform a combination of PI-led and Open-access Legacy Survey projects. Herein we provide an overview of the instrument and give the first quantitative measures of its performance in the lab prior to shipping to the telescope in 2021.

We present new arcminute-resolution maps of the Cosmic Microwave Background temperature and polarization anisotropy from the Atacama Cosmology Telescope, using data taken from 2013-2016 at 98 and 150 GHz. The maps cover more than 17,000 deg$^2$, the deepest 600 deg$^2$ with noise levels below 10 $\mu$K-arcmin. We use the power spectrum derived from almost 6,000 deg$^2$ of these maps to constrain cosmology. The ACT data enable a measurement of the angular scale of features in both the divergence-like polarization and the temperature anisotropy, tracing both the velocity and density at last-scattering. From these one can derive the distance to the last-scattering surface and thus infer the local expansion rate, $H_0$. By combining ACT data with large-scale information from WMAP we measure $H_0 = 67.6 \pm 1.1$ km/s/Mpc, at 68% confidence, in excellent agreement with the independently-measured Planck satellite estimate (from ACT alone we find $H_0 = 67.9 \pm 1.5$ km/s/Mpc). The $\Lambda$CDM model provides a good fit to the ACT data, and we find no evidence for deviations: both the spatial curvature, and the departure from the standard lensing signal in the spectrum, are zero to within 1$\sigma$; the number of relativistic species, the primordial Helium fraction, and the running of the spectral index are consistent with $\Lambda$CDM predictions to within $1.5 - 2.2\sigma$. We compare ACT, WMAP, and Planck at the parameter level and find good consistency; we investigate how the constraints on the correlated spectral index and baryon density parameters readjust when adding CMB large-scale information that ACT does not measure. The DR4 products presented here will be publicly released on the NASA Legacy Archive for Microwave Background Data Analysis., Comment: 33 pages, 24 figures, products available on the NASA LAMBDA website, version accepted for publication in JCAP

Optimal analyses of many signals in the cosmic microwave background (CMB) require map-level extraction of individual components in the microwave sky, rather than measurements at the power spectrum level alone. To date, nearly all map-level component separation in CMB analyses has been performed exclusively using satellite data. In this paper, we implement a component separation method based on the internal linear combination (ILC) approach which we have designed to optimally account for the anisotropic noise (in the 2D Fourier domain) often found in ground-based CMB experiments. Using this method, we combine multi-frequency data from the Planck satellite and the Atacama Cosmology Telescope Polarimeter (ACTPol) to construct the first wide-area, arcminute-resolution component-separated maps (covering approximately 2100 sq. deg.) of the CMB temperature anisotropy and the thermal Sunyaev-Zel'dovich (tSZ) effect sourced by the inverse-Compton scattering of CMB photons off hot, ionized gas. Our ILC pipeline allows for explicit deprojection of various contaminating signals, including a modified blackbody approximation of the cosmic infrared background (CIB) spectral energy distribution. The cleaned CMB maps will be a useful resource for CMB lensing reconstruction, kinematic SZ cross-correlations, and primordial non-Gaussianity studies. The tSZ maps will be used to study the pressure profiles of galaxies, groups, and clusters through cross-correlations with halo catalogs, with dust contamination controlled via CIB deprojection. The data products described in this paper are available on LAMBDA., Comment: 24 pages, 11 figures, matches version accepted by PRD. Data products are available on LAMBDA at https://lambda.gsfc.nasa.gov/product/act/act_dr4_derived_maps_get.cfm

One of the most important checks for systematic errors in CMB studies is the cross correlation of maps made by independent experiments. In this paper we report on the cross correlation between maps from the Atacama B-mode Search (ABS) and Atacama Cosmology Telescope (ACT) experiments in both temperature and polarization. These completely different measurements have a clear correlation with each other and with the Planck satellite in both the EE and TE spectra at $\ell, Comment: 7 pages, 5 figures. For an interactive demonstration of the methods, see https://colab.research.google.com/drive/1CnMGLn-J3pySv8A9ffNWDSlXlJWMrp2W

The Simons Observatory (SO) is an upcoming cosmic microwave background (CMB) experiment located on Cerro Toco, Chile, that will map the microwave sky in temperature and polarization in six frequency bands spanning 27 to 285 GHz. SO will consist of one 6-m large aperture telescope fielding $$\sim$$ 30,000 detectors and an array of three 0.42-m small aperture telescopes (SATs) fielding an additional 30,000 detectors. This synergy will allow for the extremely sensitive characterization of the CMB over angular scales ranging from an arcmin to tens of degrees, enabling a wide range of scientific output. Here we focus on the SATs targeting degree angular scales with successive dichroic instruments observing at mid-frequency (MF: 93/145 GHz), ultra-high-frequency (UHF: 225/285 GHz), and low-frequency (LF: 27/39 GHz). The three SATs will be able to map $$\sim$$ 10% of the sky to a noise level of $$\sim$$ $$2\,\upmu {\hbox {K}}$$ -arcmin when combining 93 and 145 GHz. The multiple frequency bands will allow the CMB to be separated from galactic foregrounds (primarily synchrotron and dust), with the primary science goal of characterizing the primordial tensor-to-scalar ratio, r, at a target level of $$\sigma (r) \approx 0.003$$ .

We present the temperature and polarization angular power spectra of the CMB measured by the Atacama Cosmology Telescope (ACT) from 5400 deg$^2$ of the 2013-2016 survey, which covers $>$15000 deg$^2$ at 98 and 150 GHz. For this analysis we adopt a blinding strategy to help avoid confirmation bias and, related to this, show numerous checks for systematic error done before unblinding. Using the likelihood for the cosmological analysis we constrain secondary sources of anisotropy and foreground emission, and derive a "CMB-only" spectrum that extends to $\ell=4000$. At large angular scales, foreground emission at 150 GHz is $\sim$1% of TT and EE within our selected regions and consistent with that found by Planck. Using the same likelihood, we obtain the cosmological parameters for $\Lambda$CDM for the ACT data alone with a prior on the optical depth of $\tau=0.065\pm0.015$. $\Lambda$CDM is a good fit. The best-fit model has a reduced $\chi^2$ of 1.07 (PTE=0.07) with $H_0=67.9\pm1.5$ km/s/Mpc. We show that the lensing BB signal is consistent with $\Lambda$CDM and limit the celestial EB polarization angle to $\psi_P =-0.07^{\circ}\pm0.09^{\circ}$. We directly cross correlate ACT with Planck and observe generally good agreement but with some discrepancies in TE. All data on which this analysis is based will be publicly released., Comment: 44 pages, 27 figures, products available on the NASA LAMBDA website, version accepted for publication in JCAP

We present new constraints on anisotropic birefringence of the cosmic microwave background polarization using two seasons of data from the Atacama Cosmology Telescope covering $456$ square degrees of sky. The birefringence power spectrum, measured using a curved-sky quadratic estimator, is consistent with zero. Our results provide the tightest current constraint on birefringence over a range of angular scales between $5$ arcminutes and $9$ degrees. We improve previous upper limits on the amplitude of a scale-invariant birefringence power spectrum by a factor of between $2$ and $3$. Assuming a nearly-massless axion field during inflation, our result is equivalent to a $2\,\sigma$ upper limit on the Chern-Simons coupling constant between axions and photons of $g_{\alpha\gamma}, Comment: 18 pages, 3 figures, Accepted for publication in PRD

TolTEC is an imaging polarimeter that will be mounted on the 50m diameter Large Millimeter Telescope (LMT) in Mexico. This camera simultaneously images the focal plane at three wavebands centered at 1.1, 1.4, and 2.0mm. TolTEC combines polarization-sensitive Kinetic Inductance Detectors (KIDs) with the LMT to produce 5-10 arcmin resolution maps of the sky in both total intensity and polarization. The light from the telescope is coupled to the TolTEC instrument using three room temperature mirrors. Before entering the cryostat, the light passes through a rapid-spinning achromatic half-wave plate, and once inside it passes through a 1 K Lyot stop that controls the telescope illumination. Inside the cryostat, a series of aluminum mirrors, silicon lenses, and dichroic filters split the light into three wavelength bands and direct each band to a different detector array. We will describe the design, and performance of the optics before installation at the telescope.

Advances in cosmic microwave background (CMB) science depend on increasing the number of sensitive detectors observing the sky. New instruments deploy large arrays of superconducting transition-edge sensor (TES) bolometers tiled densely into ever larger focal planes. High multiplexing factors reduce the thermal loading on the cryogenic receivers and simplify their design. We present the design of focal-plane modules with an order of magnitude higher multiplexing factor than has previously been achieved with TES bolometers. We focus on the novel cold readout component, which employs microwave SQUID multiplexing ($��$mux). Simons Observatory will use 49 modules containing 60,000 bolometers 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 65 $\mathrm{pA/\sqrt{Hz}}$. 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. We discuss the measured performance in the context of SO science requirements, which are exceeded., Accepted to The Astrophysical Journal

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., Comment: 9 Pages, 5 figures, Low Temperature Detectors 19

We quantify the calibration requirements for systematic uncertainties for next-generation ground-based observatories targeting the large-angle $B$-mode polarization of the Cosmic Microwave Background, with a focus on the Simons Observatory (SO). We explore uncertainties on gain calibration, bandpass center frequencies, and polarization angles, including the frequency variation of the latter across the bandpass. We find that gain calibration and bandpass center frequencies must be known to percent levels or less to avoid biases on the tensor-to-scalar ratio $r$ on the order of $\Delta r\sim10^{-3}$, in line with previous findings. Polarization angles must be calibrated to the level of a few tenths of a degree, while their frequency variation between the edges of the band must be known to ${\cal O}(10)$ degrees. Given the tightness of these calibration requirements, we explore the level to which residual uncertainties on these systematics would affect the final constraints on $r$ if included in the data model and marginalized over. We find that the additional parameter freedom does not degrade the final constraints on $r$ significantly, broadening the error bar by ${\cal O}(10\%)$ at most. We validate these results by reanalyzing the latest publicly available data from the BICEP2/Keck collaboration within an extended parameter space covering both cosmological, foreground and systematic parameters. Finally, our results are discussed in light of the instrument design and calibration studies carried out within SO., Comment: 41 pages, 18 figures

The Atacama Cosmology Telescope Polarimeter (ACTPol) is a polarization sensitive receiver for the 6-m Atacama Cosmology Telescope (ACT) and measures the small angular scale polarization anisotropies in the cosmic microwave background (CMB). The full focal plane is composed of three detector arrays, containing over 3000 transition edge sensors (TES detectors) in total. The first two detector arrays, observing at 146 GHz, were deployed in 2013 and 2014, respectively. The third and final array is composed of multichroic pixels sensitive to both 90 and 146 GHz and saw first light in February 2015. Fabricated at NIST, this dichroic array consists of 255 pixels, with a total of 1020 polarization sensitive bolometers and is coupled to the telescope with a monolithic array of broad-band silicon feedhorns. The detectors are read out using time-division SQUID multiplexing and cooled by a dilution refrigerator at 110 mK. We present an overview of the assembly and characterization of this multichroic array in the lab, and the initial detector performance in Chile. The detector array has a TES detector electrical yield of 85 %, a total array sensitivity of less than 10 $$\upmu $$ K $$\sqrt{\text {s}}$$ , and detector time constants and saturation powers suitable for ACT CMB observations.

International audience; The Simons Observatory (SO) will make precision temperature and polarization measurements of the cosmic microwave background (CMB) using a series of telescopes which will cover angular scales between one arcminute and tens of degrees and sample frequencies between 27 and 270 GHz. Here we present the current design of the large aperture telescope receiver (LATR), a 2.4m diameter cryostat that will be mounted on the SO 6m telescope and will be the largest CMB receiver to date. The cryostat size was chosen to take advantage of the large focal plane area having high Strehl ratios, which is inherent to the Cross-Dragone telescope design. The LATR will be able to accommodate thirteen optics tubes, each having a 36 cm diameter aperture and illuminating several thousand transition-edge sensor (TES) bolometers. This set of equipment will provide an opportunity to make measurements with unparalleled sensitivity. However, the size and complexity of the LATR also pose numerous technical challenges. In the following paper, we present the design of the LATR and include how we address these challenges. The solutions we develop in the process of designing the LATR will be informative for the general CMB community, and for future CMB experiments like CMB-S4.

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., Poster presented at SPIE Astronomical Telescopes & Instrumentation 2018

The Simons Observatory (SO) is a new experiment that aims to measure the cosmic microwave background (CMB) in temperature and polarization. SO will measure the polarized sky over a large range of microwave frequencies and angular scales using a combination of small (~0.5 m) and large (~6 m) aperture telescopes and will be located in the Atacama Desert in Chile. This work is part of a series of papers studying calibration, sensitivity, and systematic errors for SO. In this paper, we discuss current efforts to model optical systematic effects, how these have been used to guide the design of the SO instrument, and how these studies can be used to inform instrument design of future experiments like CMB-S4. While optical systematics studies are underway for both the small aperture and large aperture telescopes, we limit the focus of this paper to the more mature large aperture telescope design for which our studies include: pointing errors, optical distortions, beam ellipticity, cross-polar response, instrumental polarization rotation and various forms of sidelobe pickup.

Current and future Cosmic Microwave Background (CMB) polarization anisotropy measurements demand large (104-105) numbers of high-performing detectors in order to unveil minute signals. At the forefront of the detector options available to this field are transition-edge sensor (TES) bolometers, which use superconducting thin films as extremely sensitive thermistors. Understanding the behavior of these TESes is critical to leveraging their full potential and identifying trade-offs between robustness and sensitivity in their design. In this work, we report on measurements of TES bolometers designed for the Advanced ACTPol (AdvACT) upgrade to the Atacama Cosmology Telescope (ACT). Using a three-stage SQUID amplifier chain, time-division multiplexing electronics, and an external signal generator, we characterize the impedance and noise properties of a set of test TES bolometers measured in the laboratory, encompassing various designs, over a wide signal band. Using the impedance data, we are able to explore deviations from the assumed bolometer model in use for TES design and instrument sensitivity forecasts. Modeling these deviations as the result of decoupling of bolometer elements, we extract parameters describing this extended model. We are then able to compare the noise spectra of the devices to forward modeling based on the TES parameters in the extended model. We explore how excess noise varies, and conclude with a discussion of how our results can be useful for designing future TES arrays based on the expected impact of the measured effects on instrumental sensitivities, and the relevance of these results to bolometer designs for upcoming CMB experiments like Simons Observatory and CMB-S4.

International audience; The Simons Observatory (SO) will measure the cosmic microwave background (CMB) in both temperature and polarization over a wide range of angular scales and frequencies from 27-270 GHz with unprecedented sensitivity. One technology for coupling light onto the ~50 detector wafers that SO will field is spline-profiled feedhorns, which offer tunability between coupling efficiency and control of beam polarization leakage effects. We will present efforts to scale up feedhorn production for SO and their viability for future CMB experiments, including direct-machining metal feedhorn arrays and laser machining stacked Si arrays.

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 $\mu$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., Comment: Presented at SPIE Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy IX, June 15th, 2018

International audience; The Simons Observatory (SO) will provide precision polarimetry of the cosmic microwave background (CMB) using a series of telescopes which will cover angular scales from arc-minutes to tens of degrees, contain over 60,000 detectors, and observe in frequency bands between 27 GHz and 270 GHz. SO will consist of a six-meter-aperture telescope initially coupled to roughly 35,000 detectors along with an array of half-meter aperture refractive cameras, coupled to an additional 30,000+ detectors. The large aperture telescope receiver (LATR) is coupled to the SO six-meter crossed Dragone telescope and will be 2.4 m in diameter, weigh over 3 metric tons, and have five cryogenic stages (80 K, 40 K, 4 K, 1 K and 100 mK). The LATR is coupled to the telescope via 13 independent optics tubes containing cryogenic optical elements and detectors. The cryostat will be cooled by two Cryomech PT90 (80 K) and three Cryomech PT420 (40 K and 4 K) pulse tube cryocoolers, with cooling of the 1 K and 100 mK stages by a commercial dilution refrigerator system. The secondo component, the small aperture telescope (SAT), is a single optics tube refractive cameras of 42 cm diameter. Cooling of the SAT stages will be provided by two Cryomech PT420, one of which is dedicated to the dilution refrigeration system which will cool the focal plane to 100 mK. SO will deploy a total of three SATs. In order to estimate the cool down time of the camera systems given their size and complexity, a finite difference code based on an implicit solver has been written to simulate the transient thermal behavior of both cryostats. The result from the simulations presented here predict a 35 day cool down for the LATR. The simulations suggest additional heat switches between stages would be effective in distribution cool down power and reducing the time it takes for the LATR to reach its base temperatures. The SAT is predicted to cool down in one week, which meets the SO design goals.

The Simons Observatory (SO) will make precision temperature and polarization measurements of the cosmic microwave background (CMB) using a series of telescopes which will cover angular scales between one arcminute and tens of degrees, contain over 60,000 detectors, and sample frequencies between 27 and 270 GHz. SO will consist of a six-meter-aperture telescope coupled to over 30,000 detectors along with an array of half-meter aperture refractive cameras, which together couple to an additional 30,000+ detectors. SO will measure fundamental cosmological parameters of our universe, find high redshift clusters via the Sunyaev-Zeldovich effect, constrain properties of neutrinos, and seek signatures of dark matter through gravitational lensing. In this paper we will present results of the simulations of the SO large aperture telescope receiver (LATR). We will show details of simulations performed to ensure the structural integrity and thermal performance of our receiver, as well as will present the results of finite element analyses (FEA) of designs for the structural support system. Additionally, a full thermal model for the LATR will be described. The model will be used to ensure we meet our design requirements. Finally, we will present the results of FEA used to identify the primary vibrational modes, and planned methods for suppressing these modes. Design solutions to each of these problems that have been informed by simulation will be presented., Comment: 14 pages, 10 figures, Proceedings of SPIE

The Advanced ACTPol (AdvACT) upgrade to the Atacama Cosmology Telescope (ACT) features arrays of aluminum manganese transition-edge sensors (TESes) optimized for ground-based observations of the Cosmic Microwave Background (CMB). Array testing shows highly responsive detectors with anticipated in-band noise performance under optical loading. We report on TES parameters measured with impedance data taken on a subset of TESes. We then compare modeled noise spectral densities to measurements. We find excess noise at frequencies around 100 Hz, nearly outside of the signal band of CMB measurements. In addition, we describe full-array noise measurements in the laboratory and in the field for two new AdvACT mid-frequency arrays, sensitive at bands centered on 90 and 150 GHz, and data for the high-frequency array (150/230 GHz) as deployed., Comment: Accepted for publication in Journal of Low Temperature Physics for LTD-17 special issue

In the next decade, new ground-based Cosmic Microwave Background (CMB) experiments such as Simons Observatory (SO), CCAT-prime, and CMB-S4 will increase the number of detectors observing the CMB by an order of magnitude or more, dramatically improving our understanding of cosmology and astrophysics. These projects will deploy receivers with as many as hundreds of thousands of transition edge sensor (TES) bolometers coupled to Superconducting Quantum Interference Device (SQUID)-based readout systems. It is well known that superconducting devices such as TESes and SQUIDs are sensitive to magnetic fields. However, the effects of magnetic fields on TESes are not easily predicted due to the complex behavior of the superconducting transition, which motivates direct measurements of the magnetic sensitivity of these devices. We present comparative four-lead measurements of the critical temperature versus applied magnetic field of AlMn TESes varying in geometry, doping, and leg length, including Advanced ACT (AdvACT) and POLARBEAR-2/Simons Array bolometers. Molybdenum-copper bilayer ACTPol TESes are also tested and are found to be more sensitive to magnetic fields than the AlMn devices. We present an observation of weak-link-like behavior in AlMn TESes at low critical currents. We also compare measurements of magnetic sensitivity for time division multiplexing SQUIDs and frequency division multiplexing microwave rf-SQUIDs. We discuss the implications of our measurements on the magnetic shielding required for future experiments that aim to map the CMB to near-fundamental limits., 8 pages, 4 figures, conference proceedings submitted to the Journal of Low Temperature Physics

The Atacama B-mode Search (ABS) is an experiment designed to measure cosmic microwave background (CMB) polarization at large angular scales ($\ell>40$). It operated from the ACT site at 5190~m elevation in northern Chile at 145 GHz with a net sensitivity (NEQ) of 41 $��$K$\sqrt{\rm s}$. It employed an ambient-temperature sapphire half-wave plate rotating at 2.55 Hz to modulate the incident polarization signal and reduce systematic effects. We report here on the analysis of data from a 2400 deg$^2$ patch of sky centered at declination $-42^\circ$ and right ascension $25^\circ$. We perform a blind analysis. After unblinding, we find agreement with the Planck TE and EE measurements on the same region of sky. We marginally detect polarized dust emission and give an upper limit on the tensor-to-scalar ratio of $r, 38 pages, 11 figures

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., 8 pages, 4 figures, conference proceedings submitted to Journal of Low Temperature Physics; revised Fig. 2, Table 1, and text in Sec. 2, 3, author list corrected

The Simons Observatory (SO) will observe the temperature and polarization anisotropies of the cosmic microwave background (CMB) over a wide range of frequencies (27 to 270 GHz) and angular scales by using both small (∼0.5 m) and large (∼6 m) aperture telescopes. The SO small aperture telescopes will target degree angular scales where the primordial B-mode polarization signal is expected to peak. The incoming polarization signal of the small aperture telescopes will be modulated by a cryogenic, continuously-rotating half-wave plate (CRHWP) to mitigate systematic effects arising from slowly varying noise and detector pair-differencing. In this paper, we present an assessment of some systematic effects arising from using a CRHWP in the SO small aperture systems. We focus on systematic effects associated with structural properties of the HWP and effects arising when operating a HWP, including the amplitude of the HWP synchronous signal (HWPSS), and I → P (intensity to polarization) leakage that arises from detector non-linearity in the presence of a large HWPSS. We demonstrate our ability to simulate the impact of the aforementioned systematic effects in the time domain. This important step will inform mitigation strategies and design decisions to ensure that SO will meet its science goals.

Advanced ACTPol (AdvACT) will observe the temperature and polarization of the cosmic microwave background (CMB) at multiple frequencies and high resolution to place improved constraints on inflation, dark matter, and dark energy. Foregrounds from synchrotron and dust radiation are a source of contamination that must be characterized and removed across a wide range of frequencies. AdvACT will thus observe at five frequency bands from 27 to 230 GHz. We discuss the design of the pixels and feedhorns for the 27/39 GHz multichroic array for AdvACT, which will target the synchrotron radiation that dominates at these frequencies. To gain 35% in mapping speed in the 39 GHz band where the foreground signals are faintest, the pixel number was increased through reducing the pixel diameter to $$1.08\lambda $$ at the lowest frequency, which represents a 22% decrease in size compared to our previously most tightly packed pixels.

CMB-S4 is a proposed experiment to map the polarization of the Cosmic Microwave Background (CMB) to nearly the cosmic variance limit for the angular scales that are accessible from the ground. The science goals and capabilities of CMB-S4 in illuminating cosmic inflation, measuring the sum of neutrino masses, searching for relativistic relics in the early universe, characterizing dark energy and dark matter, and mapping the matter distribution in the universe have been described in the CMB-S4 Science Book. This Technology Book is a companion volume to the Science Book. The ambitious science goals of the proposed "Stage-IV" CMB-S4 will require a step forward in experimental capability from the current Stage-III experiments. To guide this process, the community summarized the current state of the technology and identify RD Receiver Optics; Focal-Plane Optical Coupling; and Focal-Plane Sensor and Readout.

We present a new measurement of the kinematic Sunyaev-Zeldovich effect using data from the Atacama Cosmology Telescope (ACT) and the Baryon Oscillation Spectroscopic Survey (BOSS). Using 600 square degrees of overlapping sky area, we evaluate the mean pairwise baryon momentum associated with the positions of 50,000 bright galaxies in the BOSS DR11 Large Scale Structure catalog. A non-zero signal arises from the large-scale motions of halos containing the sample galaxies. The data fits an analytical signal model well, with the optical depth to microwave photon scattering as a free parameter determining the overall signal amplitude. We estimate the covariance matrix of the mean pairwise momentum as a function of galaxy separation, using microwave sky simulations, jackknife evaluation, and bootstrap estimates. The most conservative simulation-based errors give signal-to-noise estimates between 3.6 and 4.1 for varying galaxy luminosity cuts. We discuss how the other error determinations can lead to higher signal-to-noise values, and consider the impact of several possible systematic errors. Estimates of the optical depth from the average thermal Sunyaev-Zeldovich signal at the sample galaxy positions are broadly consistent with those obtained from the mean pairwise momentum signal., 15 pages, 8 figures, 2 tables

The Advanced ACTPol upgrade on the Atacama Cosmology Telescope aims to improve the measurement of the cosmic microwave background anisotropies and polarization, using four new dichroic detector arrays fabricated on 150-mm silicon wafers. These bolometric cameras use AlMn transition-edge sensors, coupled to feedhorns with orthomode transducers for polarization sensitivity. The first deployed camera is sensitive to both 150 GHz and 230 GHz. Here we present the lab characterization of the thermal parameters and optical efficiencies for the two newest fielded arrays, each sensitive to both 90 GHz and 150 GHz. We provide assessments of the parameter uniformity across each array with evaluation of systematic uncertainties. Lastly, we show the arrays' initial performance in the field., Comment: Version accepted for publication by Journal of Low Temperature Physics

We present the temperature and polarization angular power spectra measured by the Atacama Cosmology Telescope Polarimeter (ACTPol). We analyze night-time data collected during 2013-14 using two detector arrays at 149 GHz, from 548 deg$^2$ of sky on the celestial equator. We use these spectra, and the spectra measured with the MBAC camera on ACT from 2008-10, in combination with Planck and WMAP data to estimate cosmological parameters from the temperature, polarization, and temperature-polarization cross-correlations. We find the new ACTPol data to be consistent with the LCDM model. The ACTPol temperature-polarization cross-spectrum now provides stronger constraints on multiple parameters than the ACTPol temperature spectrum, including the baryon density, the acoustic peak angular scale, and the derived Hubble constant. Adding the new data to planck temperature data tightens the limits on damping tail parameters, for example reducing the joint uncertainty on the number of neutrino species and the primordial helium fraction by 20%., 23 pages, 25 figures

The Atacama B-mode Search (ABS) instrument, which began observation in February of 2012, is a crossed-Dragone telescope located at an elevation of 5,100 m in the Atacama Desert in Chile. The primary scientific goal of ABS is to measure the B-mode polarization spectrum of the Cosmic Microwave Background from multipole moments of about $$\ell \approx $$ 50 to $$\ell \approx $$ 500 (angular scales from $${\sim }0.4^\circ $$ to $${\sim }4^\circ $$ ), a range that includes the primordial B-mode peak from inflationary gravitational waves. The ABS focal plane array consists of 240 pixels designed for observation at 145 GHz by the TRUCE collaboration. Each pixel has its own individual, single-moded feedhorn and contains two transition-edge sensor bolometers coupled to orthogonal polarizations that are read out using time domain multiplexing. We will report on the current status of ABS and discuss the time constants and optical efficiencies of the TRUCE detectors in the field.

We present an evaluation of systematic effects associated with a continuously-rotating, ambient-temperature half-wave plate (HWP) based on two seasons of data from the Atacama B-Mode Search (ABS) experiment located in the Atacama Desert of Chile. The ABS experiment is a microwave telescope sensitive at 145 GHz. Here we present our in-field evaluation of celestial (CMB plus galactic foreground) temperature-to-polarization leakage. We decompose the leakage into scalar, dipole, and quadrupole leakage terms. We report a scalar leakage of ~0.01%, consistent with model expectations and an order of magnitude smaller than other CMB experiments have reported. No significant dipole or quadrupole terms are detected; we constrain each to be, 11 pages, 8 figures; revision to submitted version, Fig. 5 and Eqs. (14) and (15) corrected; added Fig. 9 and description, text revisions for clarification, Fig. 5 revised for better calibration, corrected labeling errors and plotting bugs in Fig. 3, 4, and Eq. (14) and (15)

The Advanced ACTPol (AdvACT) upgrade on the Atacama Cosmology Telescope (ACT) consists of multichroic Transition Edge Sensor (TES) detector arrays to measure the Cosmic Microwave Background (CMB) polarization anisotropies in multiple frequency bands. The first AdvACT detector array, sensitive to both 150 and 230 GHz, is fabricated on a 150 mm diameter wafer and read out with a completely different scheme compared to ACTPol. Approximately 2000 TES bolometers are packed into the wafer leading to both a much denser detector density and readout circuitry. The demonstration of the assembly and integration of the AdvACT arrays is important for the next generation CMB experiments, which will continue to increase the pixel number and density. We present the detailed assembly process of the first AdvACT detector array.

The Advanced ACTPol (AdvACT) upgrade to the Atacama Cosmology Telescope features large arrays of multichroic pixels consisting of two orthogonal-polarization pairs of superconducting bolometers at two observing frequency bands. We present measurements of the detector properties and noise data in a subset of a fielded multichroic array of AlMn transition-edge sensor (TES) detectors. In this array, the distribution of critical temperature T(sub c) across detectors appears uniform at the percent level. The measured noise-equivalent power (NEP) distributions over approximately 1200 detectors are consistent with expectations. We find median NEPs of 4.0×10(exp −17) W/ √ Hz for low-band detectors and 6.2×10(exp −17) W/ √ Hz for high-band detectors under covered-window telescope test conditions with optical loading comparable to observing with precipitable water vapor approximately 0.5 mm. Lastly, we show the estimated detector optical efficiency, and demonstrate the ability to perform optical characterization over hundreds of detectors at once using a cryogenic blackbody source.

The Advanced Atacama Cosmology Telescope Polarimeter is an upgraded receiver for the Atacama Cosmology Telescope, which has begun making measurements of the small angular scale polarization anisotropies in the Cosmic Microwave Background using the first of four new multichroic superconducting detector arrays. Here, we review all details of the optimization and characterization of this first array, which features 2012 AlMn transition edge sensor bolometers operating at 150 and 230 GHz. We present critical temperatures, thermal conductivities,saturation powers, time constants, and sensitivities for the array. The results show high uniformity across the 150 mm wafer and good performance in the field.

In these proceedings, we summarize our in-field evaluation of temperature-to-polarization leakage associated with the use of a continuously-rotating, ambient-temperature half-wave plate (HWP) on the Atacama B-Mode Search (ABS) experiment. Using two seasons of data, we demonstrate scalar leakage of ∼ 0.01%. This is consistent with model expectations and an order of magnitude better than any previously-reported leakage. We constrain higher-order dipole and quadrupole leakage terms to be < 0.06% (95% confidence). Without any mitigation from scan cross-linking or boresight rotation, this corresponds to an upper limit on systematic errors in the tensor-to-scalar ratio r ;S 0.01. The HWP significantly reduces temperature-to-polarization leakage systematic errors for ABS and shows the promise of fast polarization modulation with HWPs for future experiments. Full details can be found in Ref. 1.

The Atacama Cosmology Telescope Polarimeter (ACTPol) is a polarization sensitive upgrade to the Atacama Cosmology Telescope. Located at an elevation of 5190 m, ACTPol measures the Cosmic Microwave Background (CMB) temperature and polarization with arcminute-scale angular resolution. Calibration of the detector angles is a critical step in producing maps of the CMB polarization. Polarization angle offsets in the detector calibration can cause leakage in polarization from E to B modes and induce a spurious signal in the EB and TB cross correlations, which eliminates our ability to measure potential cosmological sources of EB and TB signals, such as cosmic birefringence. We present our optical modeling and measurements associated with calibrating the detector angles in ACTPol., 12 pages, 8 figures, conference proceedings submitted to Proceedings of SPIE; added reference in section 2 and merged repeated reference

Advanced ACTPol (AdvACT) is a third-generation cosmic microwave background receiver to be deployed in 2016 on the Atacama Cosmology Telescope (ACT). Spanning five frequency bands from 25 to 280 GHz and having just over 5600 transition-edge sensor (TES) bolometers, this receiver will exhibit increased sensitivity and mapping speed compared to previously fielded ACT instruments. This paper presents the fabrication processes developed by NIST to scale to large arrays of feedhorn-coupled multichroic AlMn-based TES polarimeters on 150-mm diameter wafers. In addition to describing the streamlined fabrication process which enables high yields of densely packed detectors across larger wafers, we report the details of process improvements for sensor (AlMn) and insulator (SiN(sub x)) materials and microwave structures, and the resulting performance improvements.

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., Comment: 17 pages, 6 figures. To be published in Proc. SPIE. Presented at SPIE Astronomical Telescopes + Instrumentation Conference 9914: Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy VIII, July 2016

We present the design and the preliminary on sky performance with respect to beams and pass-bands of a multichroic polarimeter array covering the 90 and 146 GHz Cosmic Microwave Background (CMB) bands and its enabling broadband optical system recently deployed on the Atacama Cosmology Telescope (ACT). The constituent pixels are feedhorn-coupled multichroic polarimeters fabricated at NIST. This array is coupled to the ACT telescope via a set of three silicon lenses incorporating novel broad-band metamaterial anti-reflection coatings. This receiver represents the first multichroic detector array deployed for a CMB experiment and paves the way for the extensive use of multichroic detectors and broadband optical systems in the next generation of CMB experiments.

The Atacama B-Mode Search (ABS) instrument is a cryogenic ($\sim$10 K) crossed-Dragone telescope located at an elevation of 5190 m in the Atacama Desert in Chile that observed for three seasons between February 2012 and October 2014. ABS observed the Cosmic Microwave Background (CMB) at large angular scales ($40, Comment: 7 pages, 3 figures, conference proceedings submitted to the Journal of Low Temperature Detectors

We report on measurements of the cosmic microwave background (CMB) and celestial polarization at 146 GHz made with the Atacama Cosmology Telescope Polarimeter (ACTPol) in its first three months of observing. Four regions of sky covering a total of 270 square degrees were mapped with an angular resolution of $1.3'$. The map noise levels in the four regions are between 11 and 17 $\mu$K-arcmin. We present TT, TE, EE, TB, EB, and BB power spectra from three of these regions. The observed E-mode polarization power spectrum, displaying six acoustic peaks in the range $200, Comment: 16 pages, 15 figures, 5 tables