Large Helical Device

LHD
Large Helical Device
The Large Helical Device in 2014
Device typeHeliotron
LocationToki, Japan
AffiliationNational Institute for Fusion Science
Technical specifications
Major radius3.9 m (13 ft)
Minor radius0.6 m (2 ft 0 in)
Plasma volume30 m3
Magnetic field3.0 T (30,000 G)
Discharge duration54 minutes
Plasma temperature10 keV (120 MK)
Plasma density1.2×1021 m−3
History
Year(s) of operation1998–2025

The Large Helical Device (大型ヘリカル装置, Ōgata Herikaru Sōchi) (LHD) was a fusion research device located in Toki, Gifu, Japan. It was operated by the National Institute for Fusion Science (NIFS) until 2025. The LHD employed the heliotron magnetic field configuration originally developed in Japan. It was the world's largest and most powerful superconducting stellarator. In 2015, Wendelstein 7-X began operation with equal plasma volume but a weaker magnetic field. Until that time, LHD was also the largest superconducting magnetic confinement fusion device of any kind, including tokamaks.

An interior view of the vacuum vessel, which shows the LHD's superconducting coils.

The objective of the project was to conduct fusion plasma confinement research in a steady state in order to elucidate possible solutions to physics and engineering problems in helical plasma reactors. LHD is of torsatron type, which means it has only two helically-winding magnetic coils. By comparison, classical stellarators such as Wendelstein 7-A have four hellically-winding coils and a full set of circular coils outside them, while modular advanced stellarators like Wendelstein 7-X have multiple (in that case 70) separate coils with complex shape and no helical symmetry. The space between the two helical windings also automatically provides a divertor. The LHD-type torsatron is therefore suggested to be particularly simple to build at scale.

The LHD used neutral beam injection, ion cyclotron radio frequency (ICRF), and electron cyclotron resonance heating (ECRH) to heat the plasma, much like tokamaks. The helical divertor heat and particle exhaust system used the large helical coils to produce a diverting field. This configuration allows for the modification of the stochastic layer size, which is positioned between the confined plasma volume and the field lines that terminate on the divertor plate. Boundary plasma research at LHD focused on the capability of the helical divertor as an exhaust system for heliotrons and stellarators.

LHD achieved the longest sustained runs of any magnetic fusion experiment, stellarator or tokamak, at 48 minutes with 1.2x1019m-3 plasma density and 2 keV plasma temperature, and 54 minutes with 0.4x1019m-3 plasma density and 1 keV plasma temperature.

Research into the heliotron stellarator type with the aim of generating energy from fusion continues in Japan with the company Helical Fusion, founded by NIFS scientists. The company was conditionally selected for support from the Japanese government for its fusion projects in 2026.

History

See also

References

  1. 1 2 Motojima, O.; et al. (1998). "Present status of LHD construction and experimental program". Fusion Engineering and Design. 39–40 91-97. doi:10.1016/S0920-3796(97)00133-6.
  2. 1 2 Seki, T.; et al. (2025). "High Power Long Pulse Experiment by ICRF Heating in LHD". Journal of Fusion Energy. 44 59. doi:10.1007/s10894-025-00536-w.
  3. 1 2 3 Tanaka, K.; et al. (2026). "Recent advances in plasma control and physics research in the Large Helical Device". Nucl. Fusion. 66 116012. doi:10.1088/1741-4326/ae71eb.
  4. ↑ Yamada, H. (31 August 2011). "Overview of results from the Large Helical Device". Nuclear Fusion. 51 (9). doi:10.1088/0029-5515/51/9/094021.
  5. ↑ Iiyoshi, A. (20 April 1991). Development of the Stellarator/Heliotron Research (PDF) (Report). National Institute for Fusion Science, Japan. Retrieved 9 October 2026.
  6. ↑ Morisaki, T; et al. (2013). "Initial experiments towards edge plasma control with a closed helical divertor in LHD". Nucl. Fusion. 53 (6) 063014. Bibcode:2013NucFu..53f3014M. doi:10.1088/0029-5515/53/6/063014. S2CID 122537627.
  7. ↑ Bader, Aaron; Effenberg, Florian; Hegna, Chris C. (December 6, 2018). "Progress in Divertor and Edge Transport Research for Stellarator Plasmas" (PDF). Archived from the original (PDF) on 2023-07-26.
  8. ↑ "Helical selected for Japanese fusion demonstration project". World Nuclear News. 2 September 2026. Retrieved 2026-09-20.
  9. ↑ Fujiwara, M.; Yamada, H.; Ejiri, A.; Emoto, M.; Funaba, H.; Goto, M.; Ida, K.; Idei, H.; Inagaki, S.; Kado, S.; Kaneko, O.; Kawahata, K.; Kobuchi, T.; Komori, A.; Kubo, S.; Kumazawa, R.; Masuzaki, S.; Minami, T.; Miyazawa, J.; Morisaki, T.; Morita, S.; Murakami, S.; Muto, S.; Mutoh, T.; Nagayama, Y.; Nakamura, Y.; Nakanishi, H.; Narihara, K.; Nishimura, K.; et al. (1999). "Plasma confinement studies in LHD". Nuclear Fusion. 39 (11Y): 1659–1666. Bibcode:1999NucFu..39.1659F. doi:10.1088/0029-5515/39/11Y/305. S2CID 250824691. Heating by NBI of 3 MW produced plasmas with a fusion triple product of 8 × 1018m−3 keV s at a magnetic field strength of 1.5 T. An electron temperature of 1.5 keV and an ion temperature of 1.1 keV were achieved simultaneously at a line averaged electron density of 1.5 × 1019 m−3
  10. ↑ Achievement of One Hour Discharge with ECH on LHD 2005
  11. ↑ Hamaguchi, Imagawa, Obana, Yanagi and Mito (2018). "Operations of the Helium Subcooling System for the LHD HelicalCoils during Ten Plasma Experimental Campaigns". Plasma and Fusion Research. 13 3405057. Bibcode:2018PFR....1305057H. doi:10.1585/pfr.13.3405057.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  12. ↑ "Design and commissioning of the exhaust detritiation system for the Large Helical Device". ResearchGate. Retrieved 2019-03-04.
  13. ↑ 山田, 弘司. "御礼、LHD実験を完遂". 自然科学研究機構 核融合科学研究所. Retrieved 13 March 2026.

35°19′34″N 137°10′07″E / 35.32611°N 137.16861°E / 35.32611; 137.16861