The Simons Observatory (SO) is a ground-based cosmic microwave background (CMB) survey experiment that consists of three 0.5 m small-aperture telescopes (SATs) and one 6 m large-aperture telescope (LAT), sited at an elevation of 5200 m in the Atacama Desert in Chile. In order to meet the sensitivity requirements set for next-generation CMB telescopes, the LAT will deploy 30,000 transition edge sensor (TES) detectors at 100 mK across 7 optics tubes (OT), all within the Large Aperture Telescope Receiver (LATR). Additionally, the LATR has the capability to expand to 62,000 TES across 13 OTs. The LAT will be capable of making arcminute-resolution observations of the CMB, with detector bands centered at 30, 40, 90, 150, 230, and 280 GHz. We have rigorously tested the LATR systems prior to deployment in order to fully characterize the instrument and show that it can achieve the desired sensitivity levels. We show that the LATR meets cryogenic and mechanical requirements, and maintains acceptably low baseline readout noise.
The Simons Observatory is a ground-based cosmic microwave background survey experiment that consists of three 0.5 m small-aperture telescopes and one 6 m large-aperture telescope, sited at an elevation of 5200 m in the Atacama Desert in Chile. SO will deploy 60,000 transition-edge sensor (TES) bolometers in 49 separate focal-plane modules across a suite of four telescopes covering 30/40 GHz low frequency (LF), 90/150 GHz mid frequency (MF), and 220/280 GHz ultra-high frequency (UHF). Each MF and UHF focal-plane module packages 1720 optical detectors spreading across 12 detector bias lines that provide voltage biasing to the detectors. During observation, detectors are subject to varying atmospheric emission and hence need to be re-biased accordingly. The re-biasing process includes measuring the detector properties such as the TES resistance and responsivity in a fast manner. Based on the result, detectors within one bias line then are biased with suitable voltage. Here we describe a technique for re-biasing detectors in the modules using the result from bias-step measurement.
The Simons Observatory (SO) is a ground based Cosmic Microwave Background experiment that will be deployed to the Atacama Desert in Chile. SO will field over 60,000 transition edge sensor (TES) bolometers that will observe in six spectral bands between 27 GHz and 280 GHz with the goal of revealing new information about the origin and evolution of the universe. SO detectors are grouped based on their observing frequency and packaged into Universal Focal Plane Modules, each containing up to 1720 detectors which are read out using microwave SQUID multiplexing and the SLAC Microresonator Radio Frequency Electronics (SMuRF). By measuring the complex impedance of a TES we are able to access many thermoelectric properties of the detector that are difficult to determine using other calibration methods, however it has been difficult historically to measure complex impedance for many detectors at once due to high sample rate requirements. Here we present a method which uses SMuRF to measure the complex impedance of hundreds of detectors simultaneously on hour-long timescales. We compare the measured effective thermal time constants to those estimated independently with bias steps. This new method opens up the possibility for using this characterization tool both in labs and at the site to better understand the full population of SO detectors.
The Simons Observatory (SO) is a ground-based cosmic microwave background (CMB) survey experiment that consists of three 0.5 m small-aperture telescopes and one 6 m large-aperture telescope, sited at an elevation of 5200 m in the Atacama Desert in Chile. SO will utilize more than 60,000 transition edge sensors (TES) to observe CMB temperature and polarization in six frequency bands from 27-280 GHz. Common to both the small and large aperture telescope receivers (LATR) is the 300K-4K Universal Readout Harness (URH), which supports up to 600 DC bias lines and 24 radio frequency (RF) channels consisting of input and output coaxial cables, input attenuators and custom high dynamic range 40K low-noise amplifiers (LNAs) on the output readout coaxial cable. Each RF channel can read out up to 1000 TES detectors. In this paper, we will present the design and characterization of the six URHs constructed for the initial phase of SO deployment.
The Simons Observatory (SO) is a ground-based cosmic microwave background survey experiment that consists of three 0.5 m small-aperture telescopes and one 6 m large-aperture telescope, sited at an elevation of 5,200 m in the Atacama Desert in Chile. The SO focal planes will be tiled with 49 universal focal-plane modules (UFMs), in which transition-edge sensor detectors are coupled to microwave SQUID multiplexing readout components. These detector modules contain a stack of silicon wafers and chips, which are encased in an aluminum shield and electrically connected with over 10,000 wire bonds. To ensure the UFMs will maintain their electrical and mechanical integrity throughout their expected lifetime, we have developed a program of robustness testing. This program involves repeated cryogenic cycling to mimic a lifetime of operation in the field. We also describe electrical validation tools that enable the debugging of electrical shorts that can appear during assembly and device screening. As a result of these tests and developments, we expect that the UFMs will maintain operability through in-lab module screening and at least five seasons of observation in Chile.
The Simons Observatory is a suite of instruments sensitive to temperature and polarization of the cosmic microwave background. Five telescopes will host over 60,000 highly multiplexed transition edge sensor (TES) detectors. The universal focal plane modules (UFMs) package multichroic TES detectors with microwave multiplexing electronics compatible with all five receivers. The low-frequency arrays are lenslet-coupled sinuous antennas sensitive to 30 and 40 GHz. The mid-frequency and ultra-high-frequency UFMs are horn-coupled orthomode transducer arrays sensitive to 90/150 GHz and 225/280 GHz, respectively. Here we present the design, assembly details, and initial results of the first UFM.
The Simons Observatory (SO) will observe the cosmic microwave background (CMB) from Cerro Toco in the Atacama Desert of Chile. The observatory consists of three 0.5m Small Aperture Telescopes (SATs) and one 6m Large Aperture Telescope (LAT), covering six frequency bands centering around 30, 40, 90, 150, 230, and 280 GHz. The SO observations will transform our understanding of our universe by characterizing the properties of the early universe, measuring the number of relativistic species and the mass of neutrinos, improving our understanding of galaxy evolution, and constraining the properties of cosmic reionization.1 As a critical instrument, the Large Aperture Telescope Receiver (LATR) is designed to cool ~60,000 transition-edge sensors (TES)2 to <100mK on a 1.7m diameter focal plane. The unprecedented scale of the LATR drives a complex design.3-5 In this paper, We will first provide an overview of the LATR design. Integration and validation of the LATR design is discussed in detail, including mechanical strength, optical alignment, and cryogenic performance of the five cryogenic stages (80 K, 40 K, 4 K, 1 K, and 100 mK). We will also discuss the microwave- multiplexing (μMux) readout system implemented in the LATR and demonstrate operation of dark, prototype TES bolometers. The μMux readout technology enables one coaxial loop to read out Ο(103) TES detectors. Its implementation within the LATR serves as a critical validation for the complex RF chain design. The successful validation of the LATR performance is not only a critical milestone within the Simons Observatory, it also provides a valuable reference for other experiments, e.g. CCAT-prime6 and CMB-S4.7, 8
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