In-receiver performance of AliCPT-1’s first TES detector array and μmux RFSoC-based readout for CMB polarization measurements

We present the laboratory performance of a 1,704-detector microwave SQUID multiplexed (μmux) Transition-Edge Sensor (TES) array and its accompanying RFSoC-based readout electronics after integration with AliCPT-1: a 72-cm aperture, two-lens refracting CMB polarization telescope, which will observe from the Tibetan Plateau beginning in 2024. The first AliCPT-1 module incorporates two 4-6 GHz μmux readout lines, each with a multiplexing factor of 910, to readout 1,704 TES bolometers and additional dark channels. The module is probed via an RFSoC-based room-temperature electronics system, which combines all tone generation and processing procedures on a single piece of hardware. Here we describe the integration of the module and electronics with the receiver and conduct end-to-end laboratory testing of their performance. Module measurements include spectra, optical efficiency, polarization efficiency, near-field beam maps, and sensitivity to external magnetic fields. We evaluate the behavior of the readout system during optical data collection, including its noise performance.