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Overview of KAGRA: Detector design and construction history

T. Akutsu, M. Ando, K. Arai, Y. Arai, S. Araki, A. Araya, N. Aritomi, Y. Aso, S. -W. Bae, Y. -B. Bae, L. Baiotti, R. Bajpai, M. A. Barton, K. Cannon, E. Capocasa, M. -L. Chan, C. -S. Chen, K. -H. Chen, Y. -R. Chen, H. -Y. Chu, Y-K. Chu, S. Eguchi, Y. Enomoto, R. Flaminio, Y. Fujii, M. Fukunaga, M. Fukushima, G. -G. Ge, A. Hagiwara, S. Haino, K. Hasegawa, H. Hayakawa, K. Hayama, Y. Himemoto, Y. Hiranuma, N. Hirata, E. Hirose, Z. Hong, B. -H. Hsieh, G. -Z. Huang, P. -W. Huang, Y. -J. Huang, B. Ikenoue, S. Imam, K. Inayoshi, Y. Inoue, K. Ioka, Y. Itoh, K. Izumi, K. Jung, P. Jung, T. Kajita, M. Kamiizumi, N. Kanda, G. -W. Kang, K. Kawaguchi, N. Kawai, T. Kawasaki, C. Kim, J. Kim, W. Kim, Y. -M. Kim, N. Kimura, N. Kita, H. Kitazawa, Y. Kojima, K. Kokeyama, K. Komori, A. K. H. Kong, K. Kotake, C. Kozakai, R. Kozu, R. Kumar, J. Kume, C. -M. Kuo, H. -S. Kuo, S. Kuroyanagi, K. Kusayanagi, K. Kwak, H. -K. Lee, H. -W. Lee, R. -K. Lee, M. Leonardi, C. -Y. Lin, F. -L. Lin, L. C. -C. Lin, G. -C. Liu, L. -W. Luo, M. Marchio, Y. Michimura, N. Mio, O. Miyakawa, A. Miyamoto, Y. Miyazaki, K. Miyo, S. Miyoki, S. Morisaki, Y. Moriwaki, K. Nagano, S. Nagano, K. Nakamura, H. Nakano, M. Nakano, R. Nakashima, T. Narikawa, R. Negishi, W. -T. Ni, A. Nishizawa, Y. Obuchi, W. Ogaki, J. J. Oh, S. -H. Oh, M. Ohashi, N. Ohishi, M. Ohkawa, K. Okutomi, K. Oohara, C. -P. Ooi, S. Oshino, K. -C. Pan, H. -F. Pang, J. Park, F. E. Peña Arellano, I. Pinto, N. Sago, S. Saito, Y. Saito, K. Sakai, Y. Sakai, Y. Sakuno, S. Sato, T. Sato, T. Sawada, T. Sekiguchi, Y. Sekiguchi, S. Shibagaki, R. Shimizu, T. Shimoda, K. Shimode, H. Shinkai, T. Shishido, A. Shoda, K. Somiya, E. J. Son, H. Sotani, R. Sugimoto, T. Suzuki, T. Suzuki, H. Tagoshi, H. Takahashi, R. Takahashi, A. Takamori, S. Takano, H. Takeda, M. Takeda, H. Tanaka, K. Tanaka, K. Tanaka, T. Tanaka, T. Tanaka, S. Tanioka, E. N. Tapia San Martin, S. Telada, T. Tomaru, Y. Tomigami, T. Tomura, F. Travasso, L. Trozzo, T. T. L. Tsang, K. Tsubono, S. Tsuchida, T. Tsuzuki, D. Tuyenbayev, N. Uchikata, T. Uchiyama, A. Ueda, T. Uehara, K. Ueno, G. Ueshima, F. Uraguchi, T. Ushiba, M. H. P. M. van Putten, H. Vocca, J. Wang, C. -M. Wu, H. -C. Wu, S. -R. Wu, W. -R. Xu, T. Yamada, Ka. Yamamoto, Ko. Yamamoto, T. Yamamoto, K. Yokogawa, J. Yokoyama, T. Yokozawa, T. Yoshioka, H. Yuzurihara, S. Zeidler, Y. Zhao, Z. -H. Zhu

TL;DR

KAGRA introduces underground, cryogenic technology to gravitational-wave detection by employing sapphire mirrors and a sophisticated seismic isolation system, aiming to curb seismic, Newtonian, and thermal noises. The paper details the detector configuration, key noise sources, and the construction history from site selection to the first observing run, including calibration methods and readout strategies. Despite current sensitivities not matching Advanced LIGO/Virgo, KAGRA demonstrates crucial capabilities and serves as a testbed for future underground, cryogenic GW observatories, with potential gains for a global network. The work highlights remaining engineering challenges—birefringence uniformity, cryocooler reliability, and environmental noise—while outlining a path toward enhanced sensitivity and astronomical reach in subsequent observing runs.

Abstract

KAGRA is a newly built gravitational-wave telescope, a laser interferometer comprising arms with a length of 3\,km, located in Kamioka, Gifu, Japan. KAGRA was constructed under the ground and it is operated using cryogenic mirrors that help in reducing the seismic and thermal noise. Both technologies are expected to provide directions for the future of gravitational-wave telescopes. In 2019, KAGRA finished all installations with the designed configuration, which we call the baseline KAGRA. In this occasion, we present an overview of the baseline KAGRA from various viewpoints in a series of of articles. In this article, we introduce the design configurations of KAGRA with its historical background.

Overview of KAGRA: Detector design and construction history

TL;DR

KAGRA introduces underground, cryogenic technology to gravitational-wave detection by employing sapphire mirrors and a sophisticated seismic isolation system, aiming to curb seismic, Newtonian, and thermal noises. The paper details the detector configuration, key noise sources, and the construction history from site selection to the first observing run, including calibration methods and readout strategies. Despite current sensitivities not matching Advanced LIGO/Virgo, KAGRA demonstrates crucial capabilities and serves as a testbed for future underground, cryogenic GW observatories, with potential gains for a global network. The work highlights remaining engineering challenges—birefringence uniformity, cryocooler reliability, and environmental noise—while outlining a path toward enhanced sensitivity and astronomical reach in subsequent observing runs.

Abstract

KAGRA is a newly built gravitational-wave telescope, a laser interferometer comprising arms with a length of 3\,km, located in Kamioka, Gifu, Japan. KAGRA was constructed under the ground and it is operated using cryogenic mirrors that help in reducing the seismic and thermal noise. Both technologies are expected to provide directions for the future of gravitational-wave telescopes. In 2019, KAGRA finished all installations with the designed configuration, which we call the baseline KAGRA. In this occasion, we present an overview of the baseline KAGRA from various viewpoints in a series of of articles. In this article, we introduce the design configurations of KAGRA with its historical background.

Paper Structure

This paper contains 23 sections, 9 equations, 10 figures, 1 table.

Table of Contents

  1. Introduction
  2. Detector configuration
  3. Overview of interferometer
  4. Facility and vacuum system
  5. Sapphire test mass and cryogenic payload
  6. Cryogenic system
  7. Seismic isolation system
  8. Laser and input optics
  9. Output optics
  10. Digital control and calibration
  11. Sensitivity
  12. Quantum noise
  13. Thermal noise
  14. Mirror
  15. Suspension
  16. ...and 8 more sections

Figures (10)

  • Figure 1: Schematic of the KAGRA interferometer. All mirrors with labels are suspended inside the vacuum tanks with four types of vibration isolation systems. Different types of circles in the figure represent different types of vibration isolation system. Vacuum tanks in front of the input and end test masses (depicted as dotted grey circles) contain narrow angle baffles and optical systems for photon calibrator. ITMX (Y): input test mass X (Y), ETMX (Y): end test mass X (Y), BS: beam splitter, PRM: power recycling mirror, SRM: signal recycling mirror, IMMT (OMMT): input (output) mode-matching telescope, IFI (OFI): input (output) Faraday isolator.
  • Figure 2: Left: Sapphire suspension. Center: Cryogenic payload. The recoil masses for each stage are drawn in yellow, cut open so that the test mass chain inside is easier to see. Right: Type-A seismic isolation systems.
  • Figure 3: Schematic of the cooling system. Side view of the cryostat from the direction orthogonal to the arm ( left) and another side view at an angle of 30 $^\circ$ from direction indicated in the left panel ( right). Although we omitted, there is another cryocooler on the left hand side of the right panel to cool down the cooling bar and cryogenic payload.
  • Figure 4: Left: Installation of the Type-A suspension system from the second floor of the Y-end station. Center: Assembly of the Type-Bp system outside the chamber. Right: Output mode cleaner installed in the vacuum chamber.
  • Figure 5: Thermal expansion ( left), thermal conductivity ( center), and specific heat ( right) of sapphire as a function of temperature.
  • ...and 5 more figures