Adaptation of frequency-domain readout for Transition Edge Sensor bolometers for the POLARBEAR-2 Cosmic Microwave Background experiment

TL;DR

This paper discusses the development and implementation of a high-bandwidth frequency-domain multiplexing readout system for TES bolometers in the POLARBEAR-2 CMB experiment, enabling the handling of thousands of detectors for improved polarization measurements.

Contribution

It introduces the use of Digital Active Nulling to extend the multiplexing bandwidth to 3 MHz, allowing for larger TES arrays in CMB experiments.

Findings

Successfully biased a bolometer at 3 MHz

Improved cryogenic wiring to reduce parasitic inductance and resistance

Demonstrated system capability for large-scale TES readout

Abstract

The POLARBEAR-2 CosmicMicrowave Background (CMB) experiment aims to observe B-mode polarization with high sensitivity to explore gravitational lensing of CMB and inflationary gravitational waves. POLARBEAR-2 is an upgraded experiment based on POLARBEAR-1, which had first light in January 2012. For POLARBEAR-2, we will build a receiver that has 7,588 Transition Edge Sensor (TES) bolometers coupled to two-band (95 and 150 GHz) polarization-sensitive antennas. For the large array's readout, we employ digital frequency-domain multiplexing and multiplex 32 bolometers through a single superconducting quantum interference device (SQUID). An 8-bolometer frequency-domain multiplexing readout has been deployed on POLARBEAR-1 experiment. Extending that architecture to 32 bolometers requires an increase in the bandwidth of the SQUID electronics to 3 MHz. To achieve this increase in bandwidth, we use Digital Active Nulling (DAN) on the digital frequency multiplexing platform. In this paper, we present requirements and improvements on parasitic inductance and resistance of cryogenic wiring and capacitors used for modulating bolometers. These components are problematic above 1 MHz. We also show that our system is able to bias a bolometer in its superconducting transition at 3 MHz.