arXiv subjects

Suguru Takada

Publications and source records attributed to Suguru Takada.

3 recordsLinked to original sources

arXiv2023

Development of epoxy-based millimeter absorber with expanded polystyrenes and carbon black

We recently developed and characterized an absorber for millimeter wavelengths. To absorb the millimeter wave efficiently, we need to develop the low reflection and high absorption material. To meet these requirements, we tried to add polystyrene beads in the epoxy for multi-scattering in the absorber. The typical diameter of polystyrene beads corresponds to the scale of Mie scattering for the multi-scattering of photons in the absorber. The absorber consists of epoxy, carbon black, and expanded polystyrene beads. The typical size of the expanded polystyrene beads is consistent with the peak of cross-section of Mie scattering to increase the mean free path in the absorber. By applying this effect, we succeeded in improving the performance of the absorber. In this paper, we measured the optical property of epoxy for the calculation of the Mie scattering effect. Based on the calculation result, we developed the 8 types samples by changing the ratio of absorber material. To compare 8 samples, we characterized the reflectance and transmittance of the absorber in millimeter length. The measured reflectance and transmittance of 2 mm thickness sample with optimized parameter are less than 20% and 10%. We also measured the transmittance in sub-millimeter wavelength. The measured transmittance is less than 1%. The shape of absorber can be modified for any shape, such as chip and pyramidal shapes. By using this absorber, we can apply for the mitigation of stray light of millimeter wave telescope with any shapes.

astro-ph.IM↗

arXiv2021

Cryogenic suspension design for a kilometer-scale gravitational-wave detector

We report the mirror suspension design for Large-scale Cryogenic Gravitational wave Telescope, KAGRA, during bKAGRA Phase 1. Mirror thermal noise is one of the fundamental noises for room-temperature gravitational-wave detectors such as Advanced LIGO and Advanced Virgo. Thus, reduction of thermal noise is required for further improvement of their sensitivity. One effective approach for reducing thermal noise is to cool the mirrors. There are many technical challenges that must be overcome to cool the mirrors, such as cryocooler induced vibrations, thermal drift in suspensions, and reduction in duty cycling due to the increased number of potential failure mechanisms. Our mirror suspension has a black coating that makes radiative cooling more efficient. For conduction cooling, we developed ultra high purity aluminum heat links, which yield high thermal conductivity while keeping the spring constant sufficiently small. A unique inclination adjustment system, called moving mass, is used for aligning the mirror orientation in pitch. Photo-reflective displacement sensors, which have a large range, are installed for damping control on marionette recoil mass and intermediate recoil mass. Samarium cobalt magnets are used for coil-magnet actuators to prevent significant change of magnetism between room temperature and cryogenic temperature. In this paper, the design of our first cryogenic payload and its performance during bKAGRA Phase 1 are discussed.

physics.ins-det↗

arXiv2020

High Performance Heat Conductor with Small Spring Constant for Cryogenic Applications

We developed a soft and high thermal conductive heat link for cryogenic applications. The measured maximum thermal conductivity was approximately 18500 W/m/K at 10 K. This spring constant was 1/43 of that of a single thick wire with the same cross-sectional area at room temperature. We realized these performances by utilizing high purity aluminum (99.9999 %, 6N) and by stranding many thin wires that are 0.15 mm in diameter. The electrical Residual Resistivity Ratio (RRR) was also measured and used to estimate the thermal conductivity by Wiedemann-Franz law. We observed the size effect on the electrical conductivity, and evaluated the effect of mechanical deformation to the RRR. These evaluations allow us to design a pragmatic heat link for cryogenic application.

physics.ins-det↗