Cryogenic Design and Instrumentation for CMB Experiments

Abstract

The measurement of the B-mode polarization component of the cosmic microwave background (CMB) has become one of the main target in modern cosmology. Indeed, a detection of this signal would shed light on the inflationary era. However, this signal is significantly smaller compared to the E-modes polarization component or to temperature. As a consequence, the sensitivity of the instrument needs to increase. However, the development of the detectors has already reached the photon noise limit. Therefore, one possible solution is to increase the size of the focal planes. This sets significant challenges in the cryogenic design of the future CMB telescopes. Following a brief introduction regarding the CMB science and a cryogenic background, this thesis starts to describe the solution adopted for the new CMB experiments. In particular, it \textcolor{black}{discusses} the development of specific cryogenic instrumentation and also the contribution to the cryogenic design of a new CMB receiver. Two different instruments were developed for two telescopes. The first is a He4 sorption cooler designed for the Simons Array. This fridge is able to provide a cooling power of 150uW at 1K for 73 hours. The second instrument is a He3 sorption cooler designed for the instrument SWIPE, (Short Wavelength Instrument for the Polarization Explorer), on the LSPE, Large-Scale Polarization Explorer. This refrigerator is designed to maintain a constant temperature of 280mK for 7 days with an applied load of 22uW. In addition to these instruments, a commercial sorption cooler for Simons Array was also tested. The cryogenic design work was focused in creating a model for studying the transient thermal behaviour of the Simons Observatory experiment. This is dedicated to estimate the cooldown time of the receiver and sets constrains on the design of the cryostat to reduce the cooling time. In order to do that, a code was developed and it showed that a current design of the cryostat takes more 38 days to cool.

Date of Award	1 Aug 2018
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Lucio Piccirillo (Supervisor) & Patrick Weltevrede (Supervisor)