Design and performance of a cryogenic half-wave plate rotator for the Simons Observatory small aperture telescopes

Abstract

The Simons Observatory (SO) will be a cosmic microwave background (CMB) survey experiment with three small-aperture telescopes (SATs) and one large-aperture telescope, which will observe from the Atacama Desert in Chile. To control for systematics in the polarization signal, the SAT design will use a continuously rotating cryogenic half wave plate (HWP) on a high-temperature superconductor magnetic levitation bearing. This is the largest such cryogenic rotation mechanism to be deployed on a telescope to date. We will discuss the design and the mechanical and thermal performance of the SAT HWP rotator.