The Simons Observatory: the Large Aperture Telescope (LAT)

The Simons Observatory (SO) is a new Cosmic Microwave Background (CMB) experiment being built on Cerro Toco in Chile, due to begin observations in the early 2020s. The initial configuration of SO will have three small-aperture 0.5-m telescopes (SATs) and one large-aperture 6-m telescope (LAT), with a total of 60,000 transition-edge sensors (TES). The SATs will target the largest angular scales observable from Chile, mapping ~10% of the sky to a white noise level of 2 μK-arcmin in combined 93 and 145 GHz bands, to measure the primordial tensor-to-scalar ratio, r, at a target level of σ(r)=0.003. The LAT will map ~40% of the sky at arcminute angular resolution to an expected white noise level of 6 μK-arcmin in combined 93 and 145 GHz bands, overlapping with the majority of the sky area of the Legacy Survey of Space and Time (LSST) on the Vera C. Rubin Observatory sky region. It will also partially overlap with the Dark Energy Spectroscopic Instrument (DESI) field of view. Other talks in this session will describe our science forecasts with SO and the design of the SAT. This talk will present the design and status of the LAT. The SO LAT adopts a coma-corrected, 6-m aperture, crossed-Dragone optical design. The design delivers a 1.9-m diameter focal plane at a 3 mm wavelength. The telescope focal plane is re-imaged by the Large Aperture Telescope Receiver (LATR) with a size of 2.3 m in diameter and 2.6 m in length. The LATR houses 13 optics tube units that contain cold optics and TES detectors, which are read out by microwave-multiplexing. The LATR contains five temperature stages (80 K, 40 K, 4 K, 1 K, 100m K) with the coldest temperature stage capable of cooling > 70,000 detectors to < 100mK on a 1.9-m diameter focal plane.