UC San Diego
The POLARBEAR-2 Cryogenic Receiver for Cosmic Microwave Background Polarization Science
- Author(s): Howe, Logan
- Advisor(s): Keating, Brian
- et al.
Measurements of the Cosmic Microwave Background (CMB) have proved pivotal
over the last few decades in the development of ΛCDM, the standard model of cosmology.
Coupled with the standard model of particle physics, these two theories describe a majority
of our observations of the Universe’s structure, dynamics, and evolution. Beyond discovering
the specifics of how our Universe was formed, remaining open questions regarding our
Universe include the masses of neutrino species, the exact nature of dark matter, and the
equation of state of dark energy – to name a few. The CMB is imprinted with information
that can help answer all these questions, making measurements of the temperature and
polarization field of the CMB at high precision an effective path to increasing our understanding
of fundamental physics. The polarization field especially, composed of parity even
E-mode and parity odd B-mode patterns, possesses untapped constraining power, at both
very large and very small angular scales.
This dissertation describes the design and characterization of cryogenic receivers for
the Simons Array CMB polarization experiment. The Simons Array is located at 5200 m
elevation in the Atacama desert, Chile and consists of three off-axis Gregorian-Dragone
telescopes, each coupled to a POLARBEAR-2 cryogenic receiver. Each receiver’s focal plane
is comprised of 7,588 transition edge sensor (TES) bolometers cooled to 250 mK and
read out using 4 K superconducting quantum interference devices (SQUIDs) using digital
frequency division multiplexing (DfMUX). The POLARBEAR-2 receiver cryostat consists of
an optics tube and backend cryostat, which are built and tested separately, then integrated
for final testing before deployment to the Chilean site. Here we describe fabrication
and cryogenic validation of two POLARBEAR-2 backends, and of the complete second
POLARBEAR-2 receiver: POLARBEAR-2b. Additionally, we discuss readout and detector
integration, including detailed SQUID characterization and TES array measurements, and
demonstration of deployment readiness of all selected devices and subcomponents. Finally,
we describe efforts and progress towards final lab validation of the POLARBEAR-2b receiver
and final demonstrations of deployment readiness.