Readout of two-kilopixel transition-edge sensor arrays for Advanced ACTPol

TL;DR

This paper details the development and testing of a high-multiplexing readout system for large TES arrays in the Advanced ACTPol instrument, enabling precise CMB measurements with improved detector readout efficiency.

Contribution

It introduces a 64-row multiplexing architecture and automated SQUID tuning procedure for large-scale TES arrays in CMB experiments.

Findings

Successful implementation of 64-row multiplexing for TES arrays.

Optimized SQUID tuning process for large detector counts.

Enhanced readout performance with minimized noise aliasing.

Abstract

Advanced ACTPol is an instrument upgrade for the six-meter Atacama Cosmology Telescope (ACT) designed to measure the cosmic microwave background (CMB) temperature and polarization with arcminute-scale angular resolution. To achieve its science goals, Advanced ACTPol utilizes a larger readout multiplexing factor than any previous CMB experiment to measure detector arrays with approximately two thousand transition-edge sensor (TES) bolometers in each 150 mm detector wafer. We present the implementation and testing of the Advanced ACTPol time-division multiplexing readout architecture with a 64-row multiplexing factor. This includes testing of individual multichroic detector pixels and superconducting quantum interference device (SQUID) multiplexing chips as well as testing and optimizing of the integrated readout electronics. In particular, we describe the new automated multiplexing SQUID tuning procedure developed to select and optimize the thousands of SQUID parameters required to readout each Advanced ACTPol array. The multichroic detector pixels in each array use separate channels for each polarization and each of the two frequencies, such that four TESes must be read out per pixel. Challenges addressed include doubling the number of detectors per multiplexed readout channel compared to ACTPol and optimizing the Nyquist inductance to minimize detector and SQUID noise aliasing.