Published 20 Nov 2018 in gr-qc, astro-ph.IM, and physics.ins-det
Abstract: The recent detections of gravitational waves (GWs) reported by LIGO/Virgo collaborations have made significant impact on physics and astronomy. A global network of GW detectors will play a key role to solve the unknown nature of the sources in coordinated observations with astronomical telescopes and detectors. Here we introduce KAGRA (former name LCGT; Large-scale Cryogenic Gravitational wave Telescope), a new GW detector with two 3-km baseline arms arranged in the shape of an "L", located inside the Mt. Ikenoyama, Kamioka, Gifu, Japan. KAGRA's design is similar to those of the second generations such as Advanced LIGO/Virgo, but it will be operating at the cryogenic temperature with sapphire mirrors. This low temperature feature is advantageous for improving the sensitivity around 100 Hz and is considered as an important feature for the third generation GW detector concept (e.g. Einstein Telescope of Europe or Cosmic Explorer of USA). Hence, KAGRA is often called as a 2.5 generation GW detector based on laser interferometry. The installation and commissioning of KAGRA is underway and its cryogenic systems have been successfully tested in May, 2018. KAGRA's first observation run is scheduled in late 2019, aiming to join the third observation run (O3) of the advanced LIGO/Virgo network. In this work, we describe a brief history of KAGRA and highlights of main feature. We also discuss the prospects of GW observation with KAGRA in the era of O3. When operating along with the existing GW detectors, KAGRA will be helpful to locate a GW source more accurately and to determine the source parameters with higher precision, providing information for follow-up observations of a GW trigger candidate.
The paper highlights KAGRA's novel design, integrating an underground, cryogenically cooled interferometer to reduce thermal noise.
It details a 3-km arm interferometer with sapphire mirrors that achieves a sensitivity of approximately 2×10⁻²⁴/√Hz at 100 Hz.
KAGRA's deployment enhances global gravitational wave detection networks by improving source localization and fostering international collaboration.
KAGRA: A 2.5 Generation Interferometric Gravitational Wave Detector
The emergence of gravitational wave (GW) astronomy marks a milestone in astrophysics, expanding the scientific capability to observe the universe. The paper under discussion, authored by the KAGRA collaboration, introduces the KAGRA detector, which is uniquely positioned in the hierarchy of GW observatories as a 2.5 generation device. Located underground in the Ikenoyama mountain in Kamioka, Gifu, Japan, KAGRA distinguishes itself with technological innovations such as the deployment of cryogenic techniques and sapphire mirrors, enhancing its sensitivity, especially around the 100 Hz range—an essential frequency band for detecting astrophysical sources like binary black holes and neutron star mergers.
Technological and Operational Features
KAGRA employs a configuration akin to its predecessors, Advanced LIGO and Virgo, boasting a 3-km arm length resonant sideband extraction interferometer architecture. The underground location is pivotal for mitigating seismic noise, while the cryogenic cooling of mirrors to approximately 20 K reduces thermal noise. These factors collectively contribute to an anticipated sensitivity level of 2×10−24/Hz at 100 Hz. This sensitivity is comparable to that of Advanced LIGO/Virgo, thereby solidifying KAGRA’s role as an integral addition to the global network of GW detectors which includes Europe’s Einstein Telescope and the USA's Cosmic Explorer.
Implications for Gravitational Wave Astronomy
The integration of KAGRA into the international network of GW observatories such as LIGO and Virgo is expected to enhance the precision of source localization and parameter estimation. This improvement is vital for the identification of electromagnetic counterparts and the detailed paper of the universe's transient astrophysical events, a task made urgent by observations like GW170817, the seminal binary neutron star merger. KAGRA aids in the triangulation of GW signals, resolving sky locations to tens of square degrees, which is crucial for follow-up observations.
Path to Deployment and Future Prospects
Since its inception, KAGRA faced challenges typical of cutting-edge scientific infrastructure, such as delays due to seismic activity and technical hurdles like vacuum leaks. Nonetheless, progress has remained steadfast. The detector's first observational run was scheduled for late 2019, with plans to join the third observational run (O3) alongside LIGO/Virgo, culminating maximized international collaborations. KAGRA’s future prospects include contributing to searches for non-tensorial GW polarization modes and performing rigorous tests of General Relativity. Furthermore, KAGRA's roadmap involves potential enhancements aligning with upgrades observed in LIGO and Virgo’s transitions to their A+ and AdV+ phases respectively.
Collaborative and International Efforts
KAGRA’s development, carried out by an extensive international collaboration involving over 200 researchers from 90 institutions across 15 countries, underscores the cooperative spirit prevalent in GW research. The integration of this collaborative framework, manifested in initiatives like the KAGRA Algorithmic Library (KAGALI), promises innovations in GW detection technologies and methodologies.
Conclusion
As advancements in the field of gravitational wave detection continue, KAGRA stands as a testament to the efficacy of leveraging cutting-edge technology within collaborative frameworks. Its contributions have the potential to not only further the understanding of cosmic phenomena but also prepare the scientific community for future endeavors in GW research. The detector's unique cryogenic and subterranean design anticipates feasible experiments that could shape the landscape of observational astrophysics in forthcoming decades.