Cryogenic Applications in Astrophysics

Abstract

The Standard Model of Cosmology is a comprehensive theory for the history of theuniverse from the Big Bang to the present. One of the pillars of this theory is theCosmic Microwave Background (CMB) left over at Recombination and travelingthe universe since. Polarization anisotropies in the CMB offers insight into theforces acting on the primordial plasma that existed at a point in the universehidden from direct observation. Obtaining measurements of this polarization willhelp with understanding the formation of the universe and help prove the theoryof inflation that reinforces the Standard Model.Polarization observations, specifically of primordial B-modes, require the useof bolometers that operate in sub-kelvin cryogenic conditions to improve systemsensitivity. This thesis describes the development and testing of these cryogenicsubsystems, focusing on heat switches and sub-kelvin refrigerators designed forthe Simons Array. The cryogenics required to run these detectors rely on iso-lating sections of differing temperatures within the system, while retaining theability to thermally connect for temperature control, which is done using heatswitches. An active convective heat switch has been designed and tested as partof previous experiments with promising results at 1 K. Further lab testing wasdone in addition to extensive simulations to show the theory behind the designas well as offering insight for future improvements.Additional work is done on a Miniature Dilution Refrigerator (MDR) sup-ported by a double stage3He-4He sorption cooler capable of maintaining tem-peratures of 350 mK. Utilizing the precooling aspects of the sorption cooler, theMDR has been designed to operate with limited space and with low rechargetimes. This MDR was originally designed for the transition edge sensor (TES)bolometers to be utilized in the POLARBEAR-2 telescopes.

Date of Award	1 Aug 2021
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Michael Garrett (Supervisor) & Lucio Piccirillo (Supervisor)