KAGRA: 2.5 generation interferometric gravitational wave detector


The recent detections of gravitational waves (GWs) reported by the LIGO and Virgo collaborations have made a significant impact on physics and astronomy. A global network of GW detectors will play a key role in uncovering the unknown nature of the sources in coordinated observations with astronomical telescopes and detectors. Here we introduce KAGRA, a new GW detector with two 3 km baseline arms arranged in an ‘L’ shape. KAGRA’s design is similar to the second generations of Advanced LIGO and Advanced Virgo, but it will be operating at cryogenic temperatures with sapphire mirrors. This low-temperature feature is advantageous for improving the sensitivity around 100 Hz and is considered to be an important feature for the third-generation GW detector concept (for example, the Einstein Telescope of Europe or the Cosmic Explorer of the United States). Hence, KAGRA is often called a 2.5-generation GW detector based on laser interferometry. KAGRA’s first observation run is scheduled in late 2019, aiming to join the third observation run of the advanced LIGO–Virgo network. When operating along with the existing GW detectors, KAGRA will be helpful in locating GW sources more accurately and determining the source parameters with higher precision, providing information for follow-up observations of GW trigger candidates.

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Fig. 1: Location of KAGRA.
Fig. 2: Evolution of GW detectors in Japan.
Fig. 3: Observation plans of LIGO, VIRGO and KAGRA.


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This work was supported by MEXT, JSPS Leading-edge Research Infrastructure Program, JSPS Grant-in-Aid for Specially Promoted Research 26000005, JSPS Grant-in-Aid for Scientific Research on Innovative Areas 2905: JP17H06358, JP17H06361 and JP17H06364, JSPS Core-to-Core Program (A. Advanced Research Networks), JSPS Grant-in-Aid for Scientific Research (S) 17H06133, the joint research programme of the Institute for Cosmic Ray Research, University of Tokyo, National Research Foundation (NRF) grant of Korea and Computing Infrastructure Project of KISTI-GSDC in Korea, the LIGO project, and the Virgo project. The authors appreciate M. Karouzos for his kind feedback to improve the draft.

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C. Kim, Y. Michimura, H. Shinkai and A. Shoda were responsible for writing the first draft of the manuscript and incorporated comments from the collaboration in the course of completing the manuscript. All members of the KAGRA collaboration were responsible for the scope and scientific facts of the manuscript, including data analysis and the resulting figures.

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Correspondence to C. Kim or Y. Michimura or H. Shinkai or A. Shoda.

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Akutsu, T., Ando, M., Arai, K. et al. KAGRA: 2.5 generation interferometric gravitational wave detector. Nat Astron 3, 35–40 (2019). https://doi.org/10.1038/s41550-018-0658-y

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