The Simons Observatory Large Aperture Telescope Receiver

Abstract

The Simons Observatory (SO) Large Aperture Telescope Receiver (LATR) will be coupled to the Large Aperture Telescope located at an elevation of 5,200 m on Cerro Toco in Chile. 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. It cools 1200 kg of material to 4 K and 200 kg 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 Atacama Cosmology Telescope: Microwave Intensity and Polarization Maps of the Galactic Center

“…The next observational step at these frequencies will be the Large Aperture Telescope of the Simons Observatory (Ade et al 2019), anticipated to see first light in 2023 from the same site in Chile. This new instrument will have the same 6-meter diameter primary as ACT, but with an instrumented focal plane of 5 times larger area (Zhu et al 2021). The nominal scan strategy will continuously cover the entire sky in the declination range between +25 • and −40 • , providing coverage of over 100 degrees of the Galactic plane in five frequency bands in both total intensity and polarization.…”

The Simons Observatory: the Large Aperture Telescope (LAT)

“…Light entering the telescope elevation structure is reflected twice before entering the telescope camera: the Large Aperture Telescope Receiver (LATR) (Xu et al 2020;Zhu et al 2021). The LATR is mounted on a support cradle that co-rotates along the elevation structure.…”

“…Specifically, based on the 3-OT test, the fully-equipped 13-OT 100 mK stage is projected to reach <100 mK base temperature in <18 days. Thermal loading on the fully-equipped 100 mK stage is expected to be <70 µW (Xu et al 2020;Zhu et al 2021).…”

“…The right image shows the LATR from its light-receiving side. With a diameter of 2.3 m, the LATR is the largest sub-Kelvin steerable cryogenic receiver ever built(Xu et al 2020;Zhu et al 2021). The support cradle co-rotates the LATR with the elevation structure to mitigate optical systematics.…”

The Simons Observatory microwave SQUID multiplexing detector module design

“…Each SAT focal plane is comprised of seven tiled UFMs. The LAT receiver (LATR) (Zhu et al 2021) will contain seven optics tubes, each of which has a focal plane with three UFMs, for a total of 21 UFMs. The 'universal' name is given to the modules as they are common to all receiver focal planes.…”