QUBIC V: Cryogenic system design and performance

TL;DR

This paper details the design, construction, and validation of a large-volume cryogenic system for the QUBIC CMB polarization experiment, capable of continuous operation for years in harsh environments.

Contribution

It presents a novel cryogenic system design for QUBIC, integrating multiple cooling stages and validated for long-term stable operation in a challenging environment.

Findings

Cryogenic system cooled 1 m^3 instrument to 0.33K.

System operated continuously for over 6 months.

Achieved stable temperature control during tilt maneuvers.

Abstract

Current experiments aimed at measuring the polarization of the Cosmic Microwave Background (CMB) use cryogenic detector arrays and cold optical systems to boost the mapping speed of the sky survey. For these reasons, large volume cryogenic systems, with large optical windows, working continuously for years, are needed. Here we report on the cryogenic system of the QUBIC (Q and U Bolometric Interferometer for Cosmology) experiment: we describe its design, fabrication, experimental optimization and validation in the Technological Demonstrator configuration. The QUBIC cryogenic system is based on a large volume cryostat, using two pulse-tube refrigerators to cool at ~3K a large (~1 m^3) volume, heavy (~165kg) instrument, including the cryogenic polarization modulator, the corrugated feedhorns array, and the lower temperature stages; a 4He evaporator cooling at ~1K the interferometer beam combiner; a 3He evaporator cooling at ~0.3K the focal-plane detector arrays. The cryogenic system has been tested and validated for more than 6 months of continuous operation. The detector arrays have reached a stable operating temperature of 0.33K, while the polarization modulator has been operated from a ~10K base temperature. The system has been tilted to cover the boresight elevation range 20 deg -90 deg without significant temperature variations. The instrument is now ready for deployment to the high Argentinean Andes.