JT-60U

JT-60U
Name	JT-60U
Country	Japan
Type	Tokamak
Institution	Japan Atomic Energy Research Institute
Introduced	1985 (upgrade)
Retired	2008
Major upgrades	Auxiliary heating, divertor modifications, superconducting coil precursor research

JT-60U JT-60U was an upgraded high-performance tokamak operated by the Japan Atomic Energy Research Institute and later by the Japan Atomic Energy Agency at the Naka site. It served as a cornerstone of East Asian plasma research alongside international devices such as JET, TFTR, DIII-D, ASDEX Upgrade, and JT-60SA. The machine provided a platform for integrated experiments involving auxiliary heating, divertor physics, and advanced confinement regimes that informed programs at ITER, KSTAR, EAST, and national laboratories including Culham and Princeton Plasma Physics Laboratory.

Overview

JT-60U evolved from the original JT-60 project managed by the Japan Atomic Energy Research Institute and later coordinated with the Japan Atomic Energy Agency. Located at the Naka Fusion Research Establishment, the device was a large, high-current tokamak designed to explore high-beta and long-pulse scenarios relevant to next-step devices like ITER. Its operation overlapped with prominent experiments at JET and TFTR in the 1990s, contributing to the international database on confinement scaling, divertor handling, and non-inductive current drive. The facility hosted collaborations with institutes such as Oak Ridge National Laboratory, General Atomics, Max Planck Institute for Plasma Physics, and universities including University of Tokyo and Kyoto University.

Design and Upgrades

JT-60U incorporated major hardware changes from its predecessor, including a new divertor configuration inspired by modifications at ASDEX Upgrade and heating system expansions similar to upgrades at DIII-D. The machine's magnetic system allowed high plasma current and shaped configurations comparable to research at EAST and KSTAR. Auxiliary heating suites combined neutral beam injection technologies developed at Culham Centre for Fusion Energy and radiofrequency systems akin to those used at Auburn University research facilities; high-power neutral beams enabled experiments paralleling work at ORNL and GA. Divertor enhancements drew on findings from JET and Tore Supra to probe power exhaust and plasma–wall interactions. Control electronics and power supplies were periodically modernized in collaboration with industrial partners and research centers like National Institute for Fusion Science.

Operational History

Commissioned in its upgraded form in the mid-1980s, JT-60U ran campaigns through the 1990s and 2000s, often coordinated with international programs under frameworks involving IAEA and bilateral agreements with United States Department of Energy laboratories. The tokamak recorded milestone discharges that contributed to scaling relationships used by ITER designers and supported experimental campaigns aligned with efforts at JT-60SA planning. Collaborative experiments involved teams from CEA, IPP-Garching, ORNL, and universities such as Imperial College London and Massachusetts Institute of Technology. Operational challenges included heat-flux handling and material responses paralleling studies at Tore Supra and ASDEX Upgrade.

Plasma Performance and Experiments

JT-60U achieved high-performance plasmas through a combination of high plasma current, optimized magnetic shaping, and advanced heating, comparable to record-setting shots at TFTR and JET. Experiments addressed confinement regimes explored also on DIII-D and EAST, including investigations of H-mode, internal transport barriers (ITBs) studied in parallel with JET and JT-60SA design teams, and advanced scenarios for non-inductive current drive relevant to KSTAR and ITER. Research on high-beta operation and stability drew on theoretical frameworks developed at Princeton Plasma Physics Laboratory and Max Planck Institute for Plasma Physics. Edge-localized mode (ELM) behavior and mitigations paralleled work at ASDEX Upgrade and DIII-D, while divertor detachment and impurity control were coordinated with results from JET and Tore Supra.

Diagnostics and Control Systems

The diagnostic suite on JT-60U included Thomson scattering systems akin to those developed at Culham Centre for Fusion Energy, charge exchange recombination spectroscopy comparable to installations at ORNL, and microwave reflectometry similar to devices at IPP-Garching. Real-time control of plasma position and shape used algorithms influenced by control work at MIT and General Atomics, integrating magnetic probe arrays and equilibrium reconstruction codes that interfaced with heating actuators like neutral beam systems and radiofrequency launchers. Collaborations with instrumentation groups from University of Tokyo and Kyoto University advanced high-resolution diagnostics and fast feedback schemes comparable to developments at EAST and KSTAR.

Contributions to Fusion Research

JT-60U provided empirical data critical to confinement scaling laws and stability limits employed in design studies at ITER and conceptual studies for spherical tokamaks such as NSTX. Its experiments informed divertor strategies and plasma-facing component choices discussed at meetings held by IAEA and research consortia including EUROfusion. The device contributed to cross-validation of transport models developed jointly with theoretical groups at Princeton, Max Planck Institute for Plasma Physics, and CEA. Results from JT-60U influenced policy and planning documents produced by agencies such as the Japanese Ministry of Education, Culture, Sports, Science and Technology and international collaborative projects coordinated through ITER Organization partners.

Decommissioning and Legacy

JT-60U ceased operation in 2008 as focus shifted to successor projects like JT-60SA under an international collaboration between Japan and Europe. Equipment and knowledge transitioned to construction and operation of next-generation facilities including JT-60SA and informed material testing programs at sites like Wendelstein 7-X and JET. The corpus of JT-60U data remains archived and referenced in comparative studies alongside databases from DIII-D, JET, and TFTR, and its legacy continues through personnel contributions to institutions such as Japan Atomic Energy Agency and international laboratories including Culham Centre for Fusion Energy and Princeton Plasma Physics Laboratory.

Category:Tokamaks