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Optimization of Geomagnetic Shielding for MKIDs Mounted on a Rotating Cryostat


Superconducting detectors, such as microwave kinetic inductance detectors (MKIDs), are sensitive to the effects of ambient magnetic fields. There are two effects magnetic fields have on the response of MKIDs; the trapping of magnetic fields inside the superconducting materials degrades the resonator quality, and the time variation of the magnetic fields results in a baseline fluctuation. In the case of radio astronomy, this means the detector must be protected from the geomagnetic field. Here, we construct a test system to evaluate the effects described. We also evaluate the impact of the magnetic shield. We find that a shielding power of 47 dB is necessary in the case of application with a noise equivalent power of \(2.4 \times 10^{-16}\,\text {W}/\sqrt{\text {Hz}}\). We also confirm that the measured shielding power obtained using permalloy films is consistent with simulations based on the finite element method to an accuracy of 1 dB. We have designed magnetic shields for the GroundBIRD CMB telescope using these results. We achieve a sufficient shielding power of 55 dB.

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This work was supported by Grants-in-Aid for Scientific Research from The Ministry of Education, Culture, Sports, Science and Technology, Japan (KAKENHI Grant Nos. 15H05743, 15H05448, 16J09435). I am deeply grateful to Koji Ishidoshiro, Keishi Hosokawa, and Atsushi Ohno of the Research Center for Neutrino Science, Tohoku University and Tomoka Okada of the Tohoku University Astronomical Institute.

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Correspondence to Hiroki Kutsuma.

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Kutsuma, H., Hattori, M., Kiuchi, K. et al. Optimization of Geomagnetic Shielding for MKIDs Mounted on a Rotating Cryostat. J Low Temp Phys 193, 203–208 (2018).

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  • Microwave kinetic inductance detector
  • Magnetic shield
  • Cosmic Microwave Background Radiation