Vibration characteristics of a continuously rotating superconducting magnetic bearing and potential influence to TES and SQUID

Abstract: We measured the vibration of a prototype superconducting magnetic bearing (SMB) operating at liquid nitrogen temperature. This prototype system was designed as a breadboard model for LiteBIRD low-frequency telescope (LFT) polarization modulator unit. We set an upper limit of the vibration amplitude at $36~\mathrm{\mu m}$ at the rotational synchronous frequency. During the rotation, the amplitude of the magnetic field produced varies. From this setup, we compute the static and AC amplitude of the magnetic fields produced by the SMB magnet at the location of the LFT focal plane as $0.24~\mathrm{G}$ and $3\times10^{-5}$$~\mathrm{G}$, respectively. From the AC amplitude, we compute TES critical temperature variation of $7\times10^{-8}$$~\mathrm{K}$ and fractional change of the SQUID flux is $\delta \Phi/\Phi_0|_{ac}=3.1\times10^{-5}$. The mechanical vibration can be also estimated to be $3.6\times 10^{-2}$$~\mathrm{N}$ at the rotation mechanism location.