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Candidacy Exam: Measuring Cosmic Microwave Background Polarization with POLARBEAR

Tuesday November 10, 2020
2:00 pm

 Presenter:  Kayla Mitchell, UNM
 Series:  Nuclear, Particle, Astroparticle and Cosmology (NUPAC) Seminars
 Abstract:  POLARBEAR is a cosmic microwave background (CMB) polarization experiment located in the Atacama desert in Chile. The science goals of the project include a deep search for CMB B-mode polarization created by inflationary gravitational waves, as well as characterization of the CMB B-mode signal from gravitational lensing. POLARBEAR-1 observed from 2012-2017 and made initial measurements of the CMB B-mode signal. POLARBEAR/Simons Array is an expansion to three identical 3-meter telescopes with larger, more sensitive focal planes, and increased frequency coverage, with staged deployment of three new cryogenic receivers known as POLARBEAR-2a, -2b, and -2c. When completed, POLARBEAR/Simons Array will have over 20,000 superconducting transition-edge sensor bolometers, cooled to 300 mK with closed-cycle cryogenics. These detectors are read out with Dfmux frequency-division multiplexing readout, with 40 detectors read out by a series SQUID array, with frequency channels between 1 and 5 MHz defined by an inductor and capacitor in series with each detector. The array will cover 95 GHz, 150 GHz, 220 GHz, and 280 GHz frequency bands, allowing greater control of foregrounds. The PB2-b and later cryogenic readout included small modifications to improve performance, based on the integrated performance in POLARBEAR-2a. I will present my work on the characterization of the integrated cryogenic readout system for POLARBEAR-2a and POLARBEAR-2b, and comparison of properties including stray impedances, frequency scatter, and peak stability. I will also discuss my other current and future projects to improve the overall sensitivity of POLARBEAR.
 Host:  Francis-Yan Cyr-Racine
 Location:  Zoom

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