Performance of a 4 Kelvin pulse-tube cooled cryostat with dc SQUID amplifiers for bolometric detector testing

TL;DR

This paper describes the design and implementation of a cryogenic system using a pulse-tube cooler and SQUID amplifiers to test bolometric detectors for cosmic microwave background research, addressing noise and vibration challenges.

Contribution

It introduces a novel cryogenic setup combining pulse-tube cooling with SQUID amplifiers for bolometer testing, overcoming vibration and electromagnetic interference issues.

Findings

Achieved stable cooling of SQUIDs at 4 K with pulse-tube cooler.

Implemented noise reduction measures successfully.

Demonstrated effective testing environment for bolometric detectors.

Abstract

The latest generation of cosmic microwave background (CMB) telescopes is searching for the undetected faint signature of gravitational waves from inflation in the polarized signal of the CMB. To achieve the unprecedented levels of sensitivity required, these experiments use arrays of superconducting Transition Edge Sensor (TES) bolometers that are cooled to sub-Kelvin temperatures for photon-noise limited performance. These TES detectors are read out using low- noise SQUID amplifiers. To rapidly test these detectors and similar devices in a laboratory setting, we constructed a cryogenic refrigeration chain consisting of a commercial two-stage pulse-tube cooler, with a base temperature of 3 K, and a closed-cycle 3He/4He/3He sorption cooler, with a base temperature of 220 mK. A commercial dc SQUID system, with sensors cooled to 4 K, was used as a highly-sensitive cryogenic ammeter. Due to the extreme sensitivity of SQUIDs to changing magnetic fields, there are several challenges involving cooling them with pulse-tube coolers. Here we describe the successful design and implementation of measures to reduce the vibration, electromagnetic interference, and other potential sources of noise associated with pulse-tube coolers.