@article{48facad2596345718efdc1ac7c27d00c,
title = "A cryogenic continuously rotating half-wave plate mechanism for the POLARBEAR-2b cosmic microwave background receiver",
abstract = "We present the design and laboratory evaluation of a cryogenic continuously rotating half-wave plate (CHWP) for the POLARBEAR-2b (PB-2b) cosmic microwave background receiver, the second installment of the Simons Array. PB-2b will observe at 5200 m elevation in the Atacama Desert of Chile in two frequency bands centered at 90 GHz and 150 GHz. In order to suppress atmospheric 1/f noise and mitigate systematic effects that arise when differencing orthogonal detectors, PB-2b modulates linear sky polarization using a CHWP rotating at 2 Hz. The CHWP has a 440 mm clear aperture diameter and is cooled to ≈50 K in the PB-2b receiver cryostat. It consists of a low-friction superconducting magnetic bearing and a low-torque synchronous electromagnetic motor, which together dissipate <2 W. During cooldown, a grip-and-release mechanism centers the rotor to <0.5 mm, and during continuous rotation, an incremental optical encoder measures the rotor angle with a noise level of 0.1 μrad/Hz. We discuss the experimental requirements for the PB-2b CHWP, the designs of its various subsystems, and the results of its evaluation in the laboratory. The presented CHWP has been deployed to Chile and is expected to see first light on PB-2b in 2020 or 2021.",
author = "Hill, {C. A.} and A. Kusaka and P. Ashton and P. Barton and T. Adkins and K. Arnold and B. Bixler and S. Ganjam and Lee, {A. T.} and F. Matsuda and T. Matsumura and Y. Sakurai and R. Tat and Y. Zhou",
note = "Funding Information: The presented CHWP development at LBNL was supported in part by the U.S. Department of Energy, Office of Science, Office of High Energy Physics under Contract No. DE-AC02-05CH11231, as well as the LBNL Directed Research and Development (LDRD) Program. This work was also supported in part by the U.S. Department of Energy, Office of Science, Office of Workforce Development for Teachers and Scientists (WDTS) under the Science Undergraduate Laboratory Internships (SULI) program. AK acknowledges the support from JSPS Leading Initiative for Excellent Young Researchers (LEADER) and from JSPS KAKENHI under Grant Nos. JP16K21744, JP18H05539, and JP19H00674. This work was additionally supported in part by the World Premier International Research Center Initiative (WPI), MEXT, Japan. PB-2b and Simons Array, whose activities are integrated into much of the presented work, are supported by the Simons Foundation, the Gordon and Betty Moore Foundation, the Templeton Foundation, and the National Science Foundation (NSF) under Grant Nos. AST-0618398 and AST-1212230. Publisher Copyright: {\textcopyright} 2020 Author(s).",
year = "2020",
month = dec,
day = "1",
doi = "10.1063/5.0029006",
language = "English",
volume = "91",
journal = "Review of Scientific Instruments",
issn = "0034-6748",
publisher = "American Institute of Physics Publising LLC",
number = "12",
}