Compact integrated optical sensors and electromagnetic actuators for vibration isolation systems in the gravitational-wave detector KAGRA. (arXiv:2007.09571v1 [astro-ph.IM])
<a href="http://arxiv.org/find/astro-ph/1/au:+Akutsu_T/0/1/0/all/0/1">Tomotada Akutsu</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Arellano_F/0/1/0/all/0/1">Fabián Erasmo Peña Arellano</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Shoda_A/0/1/0/all/0/1">Ayaka Shoda</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Fujii_Y/0/1/0/all/0/1">Yoshinori Fujii</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Okutomi_K/0/1/0/all/0/1">Koki Okutomi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Barton_M/0/1/0/all/0/1">Mark Andrew Barton</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Takahashi_R/0/1/0/all/0/1">Ryutaro Takahashi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Komori_K/0/1/0/all/0/1">Kentaro Komori</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Aritomi_N/0/1/0/all/0/1">Naoki Aritomi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Shimoda_T/0/1/0/all/0/1">Tomofumi Shimoda</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Takano_S/0/1/0/all/0/1">Satoru Takano</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Takeda_H/0/1/0/all/0/1">Hiroki Takeda</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Martin_E/0/1/0/all/0/1">Enzo Nicolas Tapia San Martin</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kozu_R/0/1/0/all/0/1">Ryohei Kozu</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ikenoue_B/0/1/0/all/0/1">Bungo Ikenoue</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Obuchi_Y/0/1/0/all/0/1">Yoshiyuki Obuchi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Fukushima_M/0/1/0/all/0/1">Mitsuhiro Fukushima</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Aso_Y/0/1/0/all/0/1">Yoichi Aso</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Michimura_Y/0/1/0/all/0/1">Yuta Michimura</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Miyakawa_O/0/1/0/all/0/1">Osamu Miyakawa</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kamiizumi_M/0/1/0/all/0/1">Masahiro Kamiizumi</a>
This paper reports on the design and characteristics of a compact module
integrating an optical displacement sensor and an electromagnetic actuator for
use with vibration-isolation systems installed in KAGRA, the 3-km baseline
gravitational-wave detector in Japan. In technical concept, the module belongs
to a family tree of similar modules (called OSEM) used in other interferometric
gravitational-wave detector projects. After the initial test run of KAGRA in
2016, the sensor part, which is a type of fork sensor (or slot sensor), was
modified by increasing the spacing of the slot from 5 mm to 15 mm to avoid the
risk of mechanical interference with the sensor flag in operation. We confirmed
the sensor performance is comparable to that of the previous design despite the
modification. We also confirmed the sensor noise is consistent with the
theoretical noise budget. The noise level is 0.5 nm/rtHz at 1 Hz and 0.1
nm/rtHz at 10 Hz, and the linear range of the sensor is 0.7 mm or more. We
measured the response of the actuator to be 1 N/A, and also measured the
resistances and inductances of coils of the actuators to confirm their
consistency. Coupling coefficients among the different degrees of freedom were
also measured and evaluated. A potential concern about thermal noise
contribution due to eddy current loss is discussed. In addition, for reference
in the future, we summarize theoretical formulae that will be useful for
designing similar actuators. As of 2020, 42 of the modules are in operation at
the site.
This paper reports on the design and characteristics of a compact module
integrating an optical displacement sensor and an electromagnetic actuator for
use with vibration-isolation systems installed in KAGRA, the 3-km baseline
gravitational-wave detector in Japan. In technical concept, the module belongs
to a family tree of similar modules (called OSEM) used in other interferometric
gravitational-wave detector projects. After the initial test run of KAGRA in
2016, the sensor part, which is a type of fork sensor (or slot sensor), was
modified by increasing the spacing of the slot from 5 mm to 15 mm to avoid the
risk of mechanical interference with the sensor flag in operation. We confirmed
the sensor performance is comparable to that of the previous design despite the
modification. We also confirmed the sensor noise is consistent with the
theoretical noise budget. The noise level is 0.5 nm/rtHz at 1 Hz and 0.1
nm/rtHz at 10 Hz, and the linear range of the sensor is 0.7 mm or more. We
measured the response of the actuator to be 1 N/A, and also measured the
resistances and inductances of coils of the actuators to confirm their
consistency. Coupling coefficients among the different degrees of freedom were
also measured and evaluated. A potential concern about thermal noise
contribution due to eddy current loss is discussed. In addition, for reference
in the future, we summarize theoretical formulae that will be useful for
designing similar actuators. As of 2020, 42 of the modules are in operation at
the site.
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