Automated SQUID tuning procedure for kilo-pixel arrays of TES bolometers on the Atacama Cosmology Telescope

摘要

The Atacama Cosmology Telescope observes the Cosmic Microwave Background with arcminute resolutionfrom the Atacama desert in Chile. For the first observing season one array of 32 x 32 Transition EdgeSensor (TES) bolometers was installed in the primary ACT receiver, the Millimeter Bolometer Array Camera(MBAC). In the next season, three independent arrays working at 145, 220 and 280 GHz will be installed inMBAC. The three bolometer arrays are each coupled to a time-domain multiplexer developed at the NationalInstitute of Standard and Technology, Boulder, which comprises three stages of superconducting quantuminterference devices (SQUIDs). The arrays and multiplexers are read-out and controlled by the Multi ChannelElectronics (MCE) developed at the University of British Columbia, Vancouver. A number of experiments plan to use the MCE as read-out electronics and thus the procedure for tuning thethree stage SQUID system is of general interest. Here we describe the automated array tuning procedures andalgorithms we have developed. During array tuning, the SQUIDs are biased near their critical currents. SQUIDfeedback currents and lock points are selected to maximize linearity, dynamic range, and gain of the SQUIDresponse curves. Our automatic array characterization optimizes the tuning of all three stages of SQUIDs byselecting over 1100 parameters per array during the first observing season and over 2100 parameters during thesecond observing season. We discuss the timing, performance, and reliability of this array tuning procedureas well as planned and recently implemented improvements.