Laboratory Integration of the AliCPT-1 Receiver

Ali Cosmic Microwave Background (CMB) Polarization Telescope (AliCPT-1) will be the first large-scale microwave focal plane polarimeter, with > 104 detectors, dedicated to ground-based CMB observations in the Northern Hemisphere. The observatory is on the Tibetan plateau. AliCPT-1 will observe the sky with polarization sensitive Transition-Edge Sensors (TESes) in two frequency bands centered at 90 and 150 GHz. A 72 cm aperture refracting cryogenic telescope, cooled down to 4 K, will focus the sky radiation on a focal plane unit designed to host up to 32,376 detectors in 19 detector modules cooled down to 280 mK. The TESes will be read out with a microwave multiplexing architecture with a multiplexing factor up to 1,820 and a RFSoC-based room temperature readout electronics. The first detector and cryogenic multiplexer unit have been separately assembled and characterized under dark conditions. The cryostat has been successfully characterized at cryogenic temperatures, and the basic operation of the warm RFSoC system for a single detector unit has been demonstrated. Here we present the performance of the receiver before the integration of the first detector module. AliCPT-1 is a unique and powerful degree-scale CMB experiment through its combination of a unique site, large focal plane, and new enabling readout technologies.