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LiteBIRD is a space mission aimed to measure the polarization signal of the cosmic microwave background (CMB). One of the telescopes of LiteBIRD is the low-frequency telescope which has two aluminum reflectors. The reflectors are designed with thin surfaces to minimize the weight of the reflectors. Due to the thinness of the surfaces, there is a potential risk of deformation due to machining and thermal stresses. We need to establish the fabrication methodology to achieve the required surface accuracy and maintain it throughout the operation period. This paper describes the fabrication and prototyping of the half-scaled reflector and the evaluation of the surface accuracy as a demonstration. We confirmed that we can achieve an accuracy of the reflector surface of less than 10 μ m RMS. Additionally, the deformation after the thermal cycle test was less than 2 μ m RMS. These meet our requirements for CMB observation. [ABSTRACT FROM AUTHOR]

A direct detection experiment with gallium arsenide (GaAs) as a cryogenic scintillator is proposed to search for dark matter in the mass range below 1 GeV . To detect scintillation photons with high sensitivity, we are developing Lumped Element Kinetic Inductance Detectors (LE-KIDs). We report the first fabrication of the aluminum-niobium LE-KIDs and measurements of their basic properties. We designed LE-KIDs by conducting electro-magnetic simulations, and fabricated them via photolithography. We evaluated the fabricated LE-KIDs at 100 mK and detected 36 resonances out of 39 designed resonances. The resonance frequencies are roughly located at the target locations to an accuracy of 0.1 GHz , and the simulation effectively reproduced the temperature dependence of the resonance frequency. We demonstrated an optical measurement of the LE-KIDs by using an LED with wavelength that matches that of the scintillation photon from GaAs, which can operate at 100 mK . [ABSTRACT FROM AUTHOR]

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 2.4×10-16W/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. [ABSTRACT FROM AUTHOR]