JT60U

JT-60U is a tokamak fusion research device located at the Naka Fusion Institute in Naka, Ibaraki Prefecture, Japan. It is the upgrade version of the JT-60 tokamak and was developed and operated by the Japan Atomic Energy Agency (JAEA), successor to JAERI. The facility was designed to explore high-performance plasma regimes and to advance tokamak physics essential for future fusion reactors.

Design and capabilities: The upgrade increased capability for higher plasma currents and extended heating power. It used conventional copper coil magnets (non-superconducting) and employed neutral beam injection and radio-frequency heating to heat and sustain the plasma. The machine incorporated a comprehensive diagnostic suite to study confinement, stability, and reactor-relevant parameters.

Research program and contributions: JT-60U conducted experiments on high confinement modes, beta limits, and transport phenomena, contributing to understanding of plasma performance, impurity control, and steady-state operation concepts. It supported development of fueling and heating techniques applicable to next-step devices, and informed physics and engineering design for ITER and related facilities.

Legacy: JT-60U is part of Japan's contribution to international fusion research, including the Broader Approach to Fusion Energy Development between Japan and the European Union, which also supported the construction of JT-60SA, a superconducting tokamak in the same facility that continues high-performance plasma research. Operations of JT-60U ended as the JT-60SA program took precedence, marking a transition in Japan's tokamak program.