The Simons Observatory Large Aperture Telescope Receiver

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.

The Simons Observatory: Magnetic Shielding Measurements for the Universal Multiplexing Module

“…During the cooldown, the fridge was surrounded by an external high-permeability mu-metal shield to prevent magnetic flux from becoming trapped in the SQUIDs as they transition to the superconducting state. When the UMMs are deployed on SO telescopes they will be inside of a high-permeability A4K magnetic shield, as described in [6] and [7].…”

The Simons Observatory 220 and 280 GHz Focal-Plane Module: Design and Initial Characterization

“…The temperature and polarization patterns in the cosmic microwave background (CMB) give us a precise snapshot of this cosmological epoch, about 380,000 years after the big bang. Simons Observatory (SO) 1 will build four telescopes, one large-aperture telescope (LAT) [1] and three small-aperture telescopes (SATs) [2], to observe the millimeter sky from the Atacama Desert in Chile at 5,200 m. The telescopes will observe at six frequencies between 30 and 280 GHz with over 60,000 transition-edge sensor (TES) detectors. This paper focuses on the highest frequency detector modules, which have dichroic pixels centered at 220 and 280 GHz.…”

The Simons Observatory: Design and Measured Performance of a Carbon Fiber Strut for a Cryogenic Truss

“…A common approach is to support the instrument components inside the cryostat with a truss system composed of struts [3,4,6,8,10,11,12,13,14]. If the struts are properly designed, this approach delivers both the mechanical strength needed to support and align the instrument components, and the thermal isolation needed to cool the various temperature stages of the instrument.…”

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