Kavli Affiliate: Nobuhiko Katayama
| First 5 Authors: Tommaso Ghigna, Thuong Duc Hoang, Takashi Hasebe, Yurika Hoshino, Nobuhiko Katayama
| Summary:
The two most common components of several upcoming CMB experiments are large
arrays of superconductive TES (Transition-Edge Sensor) detectors and
polarization modulator units, e.g. continuously-rotating Half-Wave Plates
(HWP). A high detector count is necessary to increase the instrument raw
sensitivity, however past experiments have shown that systematic effects are
becoming one of the main limiting factors to reach the sensitivity required to
detect primordial $B$-modes. Therefore, polarization modulators have become
popular in recent years to mitigate several systematic effects. Polarization
modulators based on HWP technologies require a rotating mechanism to spin the
plate and modulate the incoming polarized signal. In order to minimize heat
dissipation from the rotating mechanism, which is a stringent requirement
particularly for a space mission like $LiteBIRD$, we can employ a
superconductive magnetic bearing to levitate the rotor and achieve contactless
rotation. A disadvantage of this technique is the associated magnetic fields
generated by those systems. In this paper we investigate the effects on a TES
detector prototype and find no detectable $T_c$ variations due to an applied
constant (DC) magnetic field, and a non-zero TES response to varying (AC)
magnetic fields. We quantify a worst-case TES responsivity to the applied AC
magnetic field of $sim10^5$ pA/G, and give a preliminary interpretation of the
pick-up mechanism.
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