164 research outputs found
Thermal-noise-limited underground interferometer CLIO
We report on the current status of CLIO (Cryogenic Laser Interferometer
Observatory), which is a prototype interferometer for LCGT (Large Scale
Cryogenic Gravitational-Wave Telescope). LCGT is a Japanese next-generation
interferometric gravitational wave detector featuring the use of cryogenic
mirrors and a quiet underground site. The main purpose of CLIO is to
demonstrate a reduction of the mirror thermal noise by cooling the sapphire
mirrors. CLIO is located in an underground site of the Kamioka mine, 1000 m
deep from the mountain top, to verify its advantages. After a few years of
commissioning work, we have achieved a thermal-noise-limited sensitivity at
room temperature. One of the main results of noise hunting was the elimination
of thermal noise caused by a conductive coil-holder coupled with a pendulum
through magnets.Comment: 10 pages, 6 figures, Proceedings of the 8th Edoardo Amaldi Conference
on Gravitational Wave
Three dimensional structure of low-density nuclear matter
We numerically explore the pasta structures and properties of low-density
nuclear matter without any assumption on the geometry. We observe conventional
pasta structures, while a mixture of the pasta structures appears as a
metastable state at some transient densities. We also discuss the lattice
structure of droplets.Comment: 6 pages, 8 figure
Reduction of thermal fluctuations in a cryogenic laser interferometric gravitational wave detector
The thermal fluctuation of mirror surfaces is the fundamental limitation for
interferometric gravitational wave (GW) detectors. Here, we experimentally
demonstrate for the first time a reduction in a mirror's thermal fluctuation in
a GW detector with sapphire mirrors from the Cryogenic Laser Interferometer
Observatory at 17\,K and 18\,K. The detector sensitivity, which was limited by
the mirror's thermal fluctuation at room temperature, was improved in the
frequency range of 90\,Hz to 240\,Hz by cooling the mirrors. The improved
sensitivity reached a maximum of at 165\,Hz.Comment: Accepted for publication in Physical Review Letters, 5 pages, 2
figure
Search for a stochastic background of 100-MHz gravitational waves with laser interferometers
This letter reports the results of a search for a stochastic background of
gravitational waves (GW) at 100 MHz by laser interferometry. We have developed
a GW detector, which is a pair of 75-cm baseline synchronous recycling
(resonant recycling) interferometers. Each interferometer has a strain
sensitivity of ~ 10^{-16} Hz^{-1/2} at 100 MHz. By cross-correlating the
outputs of the two interferometers within 1000 seconds, we found h_{100}^2
Omega_{gw} < 6 times 10^{25} to be an upper limit on the energy density
spectrum of the GW background in a 2-kHz bandwidth around 100 MHz, where a flat
spectrum is assumed.Comment: Accepted by Phys.Rev.Lett.; 10 pages, 4 figure
Effects of hydrogen ion irradiation on zinc oxide etching
Mechanisms of zinc oxide (ZnO) etching by hydrocarbon plasmas were investigated both experimentally and theoretically with the use of a mass-selected ion beam system and first-principle quantum mechanical (QM) simulation based on the density functional theory. The mass-selected ion beam experiments have shown that the sputtering yield of ZnO increases by a pretreatment of the ZnO film by energetic hydrogen (H) ion injections prior to heavy ion bombardment, suggesting that chemically enhanced etching of ZnO by hydrocarbon plasmas is closely related to hydrogen storage and/or formation of damage in the ZnO layer by energetic hydrogen injections. In this study, the effects of hydrogen storage in ZnO are examined. First-principle QM simulation of ZnO interacting with H atoms has shown that H atoms in ZnO form hydroxyl (OH) groups (or partially convert ZnO to ZnOH), which results in the weakening or breaking of the Zn-O bonds around H atoms and thus makes the ZnO film more prone to physical sputtering. The formation of hydroxyl groups in ZnO is also expected to occur in ZnO etching by hydrocarbon plasmas and increase its sputtering yields over those by inert-gas plasmas generated under similar conditions.H. Li et al., Journal of Vacuum Science & Technology A 35, 05C303 (2017) https://doi.org/10.1116/1.498271
Current status of Japanese detectors
Current status of TAMA and CLIO detectors in Japan is reported in this
article. These two interferometric gravitational-wave detectors are being
developed for the large cryogenic gravitational wave telescope (LCGT) which is
a future plan for detecting gravitational wave signals at least once per year.
TAMA300 is being upgraded to improve the sensitivity in low frequency region
after the last observation experiment in 2004. To reduce the seismic noises, we
are installing new seismic isolation system, which is called TAMA Seismic
Attenuation System, for the four test masses. We confirmed stable mass locks of
a cavity and improvements of length and angular fluctuations by using two SASs.
We are currently optimizing the performance of the third and fourth SASs. We
continue TAMA300 operation and R&D studies for LCGT. Next data taking in the
summer of 2007 is planned.
CLIO is a 100-m baseline length prototype detector for LCGT to investigate
interferometer performance in cryogenic condition. The key features of CLIO are
that it locates Kamioka underground site for low seismic noise level, and
adopts cryogenic Sapphire mirrors for low thermal noise level. The first
operation of the cryogenic interferometer was successfully demonstrated in
February of 2006. Current sensitivity at room temperature is close to the
target sensitivity within a factor of 4. Several observation experiments at
room temperature have been done. Once the displacement noise reaches at thermal
noise level of room temperature, its improvement by cooling test mass mirrors
should be demonstrated.Comment: 6 pages, 5 figures, Proceedings of GWDAW-1
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