JT-60

JT-60. It was a major tokamak nuclear fusion research device located at the Naka Fusion Institute in Ibaraki Prefecture, operated by the Japan Atomic Energy Agency and its predecessor organizations. The facility was constructed to advance the scientific understanding of plasma physics and to support the development of future fusion power plants, playing a complementary role to other large international devices like JET and TFTR.

Overview

The project was initiated in the 1970s as part of Japan's national fusion energy program, with construction beginning in 1978. Achieving its first plasma in 1985, it quickly became a cornerstone of global fusion research. Throughout its operational lifetime, it collaborated extensively with other major laboratories, including those involved in the ITER project. The original device concluded its experimental campaigns in 2008, making way for a significant upgrade.

Design and technical specifications

The device was a large, D-shaped tokamak with a major radius of approximately 3.4 meters and a minor radius of about 1.0 meter. Its vacuum vessel was constructed from Inconel and designed to withstand high heat fluxes and electromagnetic forces. For plasma heating and current drive, it employed powerful neutral beam injection systems, ion cyclotron resonance heating, and lower hybrid current drive. The toroidal field was generated by superconducting niobium-titanium magnets in later configurations, allowing for extended pulse durations. Key diagnostic tools included Thomson scattering, charge exchange recombination spectroscopy, and magnetic probes for detailed plasma analysis.

Research objectives and achievements

A primary goal was to achieve high-performance plasma conditions relevant to a future fusion reactor. It set a world record for the highest value of the fusion triple product, a key measure of progress toward ignition, in 1996. The device extensively studied advanced plasma regimes, including high-confinement H-mode and steady-state scenarios with a high fraction of bootstrap current. It made significant contributions to understanding plasma stability, disruptions, and the control of impurities and divertor heat loads. Its research directly informed the design and operational planning for ITER and DEMO.

Upgrades and future developments

Following the final experiment of the original machine, a major upgrade project began to transform it into JT-60SA. This project is a joint undertaking between the Japan Atomic Energy Agency and the European Union through Fusion for Energy. The new device features fully superconducting coils and is designed to investigate steady-state, high-beta plasmas. JT-60SA is considered a satellite facility to ITER, intended to resolve key physics and engineering issues in support of the DEMO reactor roadmap. Its first plasma was achieved in 2023.

Significance and impact

The device is widely regarded as one of the most successful and influential tokamaks in history. Its extensive database on plasma confinement, stability, and heating has been critical for validating theoretical models and simulation codes used worldwide. The expertise developed by its team has greatly contributed to international projects like ITER and the broader global fusion community. Its evolution into JT-60SA ensures its legacy continues, positioning it to play a vital role in the final steps toward the realization of practical fusion power.

Category:Experimental nuclear fusion reactors Category:Tokamaks Category:Research and development in Japan