Half-meter Scale Superconducting Magnetic Bearing for Cosmic Microwave Background Polarization Experiments

Yuki Sakurai, Peter Ashton, Akito Kusaka, Charles A. Hill, Kenji Kiuchi, Nobuhiko Katayama, Osamu Tajima

Research output: Contribution to journalConference articlepeer-review

2 Citations (Scopus)


We report the development of a large-diameter superconducting magnetic bearing (SMB) used in a continuously rotating cryogenic half-wave plate (HWP) polarization modulator for cosmic microwave background (CMB) polarization experiments. A precise measurement of the CMB polarization will place tighter constrains on cosmic inflation, describing the rapid expansion of the early universe. The polarization modulator is a critical instrument for suppressing 1/f contamination, which is mainly caused by atmospheric noise, and for mitigating systematic uncertainties that arise when differencing orthogonal polarization detectors. To ensure a sufficient field of view and to reduce thermal emission, the polarization modulator must have a clear-aperture diameter of > 500 mm and must operate at cryogenic temperatures. We constructed a superconducting magnetic bearing (SMB) with an inner diameter of 550 mm, which is the largest used in any CMB polarization experiment to date. We tested the friction and stiffness of the bearing at liquid nitrogen temperatures. The measured total loss is 0.4 W and the spring constant is >105 N/m, which satisfies typical experimental requirements. Furthermore, we performed a performance test by changing the number of disk-shaped YBCO tiles, and then confirmed that the SMB performance was proportional to the YBCO volume.

Original languageEnglish
Article number012060
JournalJournal of Physics: Conference Series
Issue number1
Publication statusPublished - Jul 31 2020
Externally publishedYes
Event32nd International Symposium on Superconductivity, ISS 2019 - Kyoto, Japan
Duration: Dec 3 2019Dec 5 2019

ASJC Scopus subject areas

  • Physics and Astronomy(all)


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