National Institute for Fusion Science

The Large Helical Device (LHD) is a superconducting helical stellarator (heliotron) operated by the National Institute for Fusion Science (NIFS) in Japan. Since beginning operation in 1998, LHD has pursued steady-state, high-temperature plasma confinement as a pathfinder for helical stellarator fusion approach. It has demonstrated plasmas with ion and electron temperatures reaching over 100 million degrees Celsius, establishing reactor-relevant high-temperature operation in a stellarator configuration. LHD was constructed on time and on budget through the efforts and capabilities of Japanese engineering companies, demonstrating Japan’s strength in large-scale, high-precision fusion engineering.

LHD has also set landmark records for long-pulse operation, sustaining high-temperature plasmas for more than 3,000 seconds (about one hour), thereby experimentally demonstrating steady-state capability with superconducting coils and continuous heating systems. In terms of overall performance, LHD has achieved fusion triple products exceeding 10¹⁹ keV·s/m³, in the same order of magnitude as the high-performance discharges reported on Germany’s Wendelstein 7-X stellarator, underscoring the competitiveness of the stellarator approach to magnetic confinement fusion.