Construction of KAGRA: an Underground Gravitational Wave Observatory

TL;DR

KAGRA is a second-generation underground gravitational-wave detector built in a mine, achieving low-frequency sensitivity and stability, with initial tests demonstrating its operational feasibility and advantages of underground construction.

Contribution

This paper details the construction and initial operation of KAGRA, highlighting the benefits and challenges of underground detector design and the integration with geophysics instruments.

Findings

Successful installation and initial testing of KAGRA in 2016

Demonstrated low-frequency sensitivity benefits of underground placement

Operational integration with geophysics interferometer

Abstract

Major construction and initial-phase operation of a second-generation gravitational-wave detector KAGRA has been completed. The entire 3-km detector is installed underground in a mine in order to be isolated from background seismic vibrations on the surface. This allows us to achieve a good sensitivity at low frequencies and high stability of the detector. Bare-bones equipment for the interferometer operation has been installed and the first test run was accomplished in March and April of 2016 with a rather simple configuration. The initial configuration of KAGRA is named {\it iKAGRA}. In this paper, we summarize the construction of KAGRA, including the study of the advantages and challenges of building an underground detector and the operation of the iKAGRA interferometer together with the geophysics interferometer that has been constructed in the same tunnel.