Abstract
Abstract The Simons Observatory is a ground-based cosmic microwave background experiment that consists of three 0.4 m small-aperture telescopes and one 6 m Large Aperture Telescope, located at an elevation of 5300 m on Cerro Toco in Chile. The Simons Observatory Large Aperture Telescope Receiver (LATR) is the cryogenic camera that will be coupled to the Large Aperture Telescope. The resulting instrument will produce arcminute-resolution millimeter-wave maps of half the sky with unprecedented precision. The LATR is the largest cryogenic millimeter-wave camera built to date, with a diameter of 2.4 m and a length of 2.6 m. The coldest stage of the camera is cooled to 100 mK, the operating temperature of the bolometric detectors with bands centered around 27, 39, 93, 145, 225, and 280 GHz. Ultimately, the LATR will accommodate 13 40 cm diameter optics tubes, each with three detector wafers and a total of 62,000 detectors. The LATR design must simultaneously maintain the optical alignment of the system, control stray light, provide cryogenic isolation, limit thermal gradients, and minimize the time to cool the system from room temperature to 100 mK. The interplay between these competing factors poses unique challenges. We discuss the trade studies involved with the design, the final optimization, the construction, and ultimate performance of the system.
Highlights
Observations of the cosmic microwave background (CMB) are a crucial tools in developing our understanding of the physics of the early universe and testing the standard model of cosmology, ΛCDM
The design of the Large Aperture Telescope Receiver (LATR) vacuum shell is driven by the requirements of being able to withstand atmospheric pressure, the mechanical interfaces associated with mounting it in the Large Aperture Telescope (LAT), and the desire to minimize the mass that the co-rotating LAT interface would need to support
This means that when we extrapolate the loading to 13 optics tubes (OTs), the warmest OT focal plane stage will be at most 92 mK, accounting for the uncertainty in our measurement of the 100 mK loading from one OT
Summary
Observations of the cosmic microwave background (CMB) are a crucial tools in developing our understanding of the physics of the early universe and testing the standard model of cosmology, ΛCDM While satellite missions such as the Cosmic Background Explorer (COBE) (Smoot 1999), the Wilkinson Microwave Anisotropy Probe (WMAP) (Bennett et al 2013; Hinshaw et al 2013), and the Planck Collaboration (Planck Collaboration et al 2020) have produced full-sky microwave maps, ground-based experiments have extended the satellite measurements towards smaller angular scales and lower noise levels. The LAT will be able to make precise measurements of the small-scale temperature and polarization power spectra, as well as the CMB lensing spectrum (The Simons Observatory Collaboration et al 2019). Note—The SO LAT projected survey sensitivity with fsky = 0.4 (The Simons Observatory Collaboration et al 2019) This represents the nominal configuration for the first deployment, with seven of the 13 OTs installed (see Section 3.3 for OT design).
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