Development and status of cryogenic half wave plate polarization modulators for Simons Observatory and Simons Array

B-Mode Polarization of the Cosmic Microwave Background (CMB) provides a probe into the structure of the early universe. The small magnitude of this polarization requires modern CMB experiments to rigorously remove unwanted noise sources. Many of these noise sources manifest in detectors as so-called 1/f noise. To remove this noise, a standard experimental technique is to implement a rotating half-wave plate, which modulates the CMB polarization above the low frequency cutoff. We present the status, control software, and initial characterization of two continuously rotating “cryogenic” half-wave plates (CHWP), the first integrated into the POLARBEAR-2B (PB2b) receiver of the Simons Array and the second integrated into the Small Aperture Telescope (SAT-MF1) receiver of the Simons Observatory. In particular, we highlight recent commissioning data taken at the Chilean site.