arXiv subjects

Yoshio Saito

Publications and source records attributed to Yoshio Saito.

4 recordsLinked to original sources

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↗

arXiv2019

Mirror actuation design for the interferometer control of the KAGRA gravitational wave telescope

KAGRA is a 3-km cryogenic interferometric gravitational wave telescope located at an underground site in Japan. In order to achieve its target sensitivity, the relative positions of the mirrors of the interferometer must be finely adjusted with attached actuators. We have developed a model to simulate the length control loops of the KAGRA interferometer with realistic suspension responses and various noises for mirror actuation. Using our model, we have designed the actuation parameters to have sufficient force range to acquire lock as well as to control all the length degrees of freedom without introducing excess noise.

physics.ins-det↗

arXiv2018

Molecular adsorbed layer formation on cooled mirrors and its impacts on cryogenic gravitational wave telescopes

Cryogenic mirrors have been introduced to the KAGRA gravitational wave telescope in Japan, and are also planned to be used in next-generation gravitational wave telescopes to further improve their sensitivity. Molecular gases inside vacuum chambers adhere to cold mirror surfaces because they lose their kinetic energy when they hit cryogenic surfaces. Finally, a number of adsorbed molecules form an adlayer, which will grow with time. The growing adlayer functions as an optical coating and changes the properties of the underlying mirror, such as reflectance, transmittance, and absorption, which are carefully chosen to maximize the detector sensitivity. The adlayer possibly affects the gravitational wave detector sensitivity. In order to characterize these changes, a high-finesse Fabry--Perot cavity was introduced to a KAGRA cryostat and the finesse of the cavity was monitored for 35 days under cryogenic conditions. We confirmed that the molecular adlayer was formed on a cold mirror and caused an oscillation in the finesse. The real and imaginary parts of the refractive index of the adlayer were $1.26 \pm 0.073$ and $2.2 \times 10^{-7} \pm 1.3 \times 10^{-7} $, respectively. These are considered to be that of $\mathrm{H_2O}$ molecules. The formation rate of the molecular adlayer was 27 $\pm$ 1.9 $\mathrm{nm/day}$. In this paper, we describe theoretical and experimental studies of the formation of a molecular adlayer on cryogenic mirrors. Furthermore, the effects of a molecular adlayer on the quantum noise and the input heat to the test mass are also discussed.

gr-qc↗

arXiv2007

Conduction Effect of Thermal Radiation in a Metal Shield Pipe in a Cryostat for a Cryogenic Interferometric Gravitational Wave Detector

A large heat load caused by thermal radiation through a metal shield pipe was observed in a cooling test of a cryostat for a prototype of a cryogenic interferometric gravitational wave detector. The heat load was approximately 1000 times larger than the value calculated by the Stefan-Boltzmann law. We studied this phenomenon by simulation and experiment and found that it was caused by the conduction of thermal radiation in a metal shield pipe.

physics.ins-det↗