Characterization of a high-temperature superconducting bearing for use in a cosmic microwave background polarimeter

We have previously presented a design for a cosmic microwave background (CMB) polarimeter in which a cryogenically cooled half-wave plate rotates by means of a high-temperature superconducting (HTS) bearing. Here, a prototype bearing, consisting of a commercially available ring-shaped permanent magnet and an array of YBCO bulk HTS material, has been constructed. We measured its coefficient of friction and vibrational property as a function of several parameters, including temperature between 15 and 83 K, rotation frequency between 0.3 and 3.5 Hz, levitation distance between 6 and 10 mm and ambient pressure of ∼10^-7 Torr. We concluded that the low rotational drag of the HTS bearing would allow rotations for long periods with minimal input power and negligible wear and tear, thus making this technology suitable for a future satellite mission.