2017 upgrade and performance of BICEP3: a 95GHz refracting telescope for degree-scale CMB polarization

TL;DR

BICEP3 is a 95GHz refracting telescope designed for CMB polarization measurements, which underwent upgrades in 2017 to improve noise performance and mapping speed, achieving significant advancements over previous instruments.

Contribution

This paper reports the 2017 upgrade of BICEP3, enhancing its optical elements for better noise performance and demonstrating improved mapping speed and sensitivity.

Findings

Achieved an order-of-magnitude increase in mapping speed.

Demonstrated $6.6\mu K\sqrt{s}$ noise performance.

Operational since 2014-15 at the South Pole with upgraded optical components.

Abstract

BICEP3 is a 520mm aperture on-axis refracting telescope observing the polarization of the cosmic microwave background (CMB) at 95GHz in search of the B-mode signal originating from inflationary gravitational waves. BICEP3's focal plane is populated with modularized tiles of antenna-coupled transition edge sensor (TES) bolometers. BICEP3 was deployed to the South Pole during 2014-15 austral summer and has been operational since. During the 2016-17 austral summer, we implemented changes to optical elements that lead to better noise performance. We discuss this upgrade and show the performance of BICEP3 at its full mapping speed from the 2017 and 2018 observing seasons. BICEP3 achieves an order-of-magnitude improvement in mapping speed compared to a Keck 95GHz receiver. We demonstrate $6.6\mu K\sqrt{s}$ noise performance of the BICEP3 receiver.