DEVELOPMENT OF CRYOGENIC SYSTEMS FOR CMB POLARIZATION OBSERVATIONS

Abstract

The history of the Universe is described by the Standard Model of Cosmology. This is commonly referred to as the Lambda-CDM model, as it describes the evolution of the Universe in terms of its main components, Dark energy (Lambda) and Cold Dark Matter. Great progress in precision Cosmology, particularly due to the measurements of the Cosmic Microwave Background (CMB) radiation, has allowed to establish the Standard Lambda-CDM Model to describe the evolution of the Universe. The forthcoming CMB observatories will record data across a range of frequencies and angular scales in order to measure the CMB B-modes. These measurements will support a large number of science goals, providing direct evidence for theories of inflation, whilst also measuring the properties of neutrinos, and further con- straining cosmological parameters to enable multiple probes of the growth rate of structure of the Universe. These outstanding science goals require exceptional instrument capabilities. In particular, sub-kelvin cryogenic temperatures are needed to support the required sensitivites of the receivers. This thesis reports the development of several cryogenic subsystems which support CMB B-modes observations. These have been developed to support the sub-kelvin operation of the receiver and the preliminary detector and readout testing. Optimisation of a 4He sorption cooler with high capacity has been reported, which operates at 1 K the large optical throughput of the QUBIC (the Q & U Bolometric Interferometer) for Cosmology receiver. Alongside this, novel convective heat switches have been characterised and tested, which precool the 1 K stage and provide isolation whilst the cooler is recycled. A design for a double stage 3He/4He sorption cooler has been developed which supports testing of SQUIDs (Superconducting Quantum Interference Devices) readout at 350 mK within a dedicated magneto-optical cryostat. Furthermore, a novel Miniature Dilution Refrigerator (MDR) has been developed to support the fast-turnaround operation of detector wafer test cryostats. This has been originally designed to support the increasing production of arrays of transition edge sensor bolometer based detectors for the Simons Observatory, whose focal planes are operated at 100 mK.

Date of Award	1 Aug 2020
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Richard Battye (Supervisor) & Lucio Piccirillo (Supervisor)