Large Helical Device

The Large Helical Device (大型ヘリカル装置, Ōgata Herikaru Sōchi) (LHD) is a fusion research device located in Toki, Gifu, Japan. It is operated by the National Institute for Fusion Science, and is the world's second-largest superconducting stellarator, after Wendelstein 7-X. The LHD employs a heliotron magnetic field originally developed in Japan.

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

LHD

Large Helical Device
The Large Helical Device in 2014
Device type	Heliotron
Location	Toki, Japan
Affiliation	National Institute for Fusion Science
Technical specifications
Major radius	3.9 m (13 ft)
Minor radius	0.6 m (2 ft 0 in)
Magnetic field	3.0 T (30,000 G)
History
Year(s) of operation	1998–present

The objective of the project is 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. The LHD uses neutral beam injection, ion cyclotron radio frequency (ICRF), and electron cyclotron resonance heating (ECRH) to heat the plasma, much like conventional tokamaks. The helical divertor heat and particle exhaust system uses 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 focuses on the capability of the helical divertor as an exhaust system for heliotrons and stellarators.^[1][2]

History

• Design finalized 1987
• Start of construction 1990
• Plasma operations from 1998
• Neutral beam injection of 3 MW was used in 1999.^[3]
• In 2005 it maintained a plasma for 3,900 seconds.^[4]
• In 2006 a new helium cooler was added. Using the new cooler, by 2018 a total of 10 long term operations have been achieved, reaching a maximum power level of 11.833 kA.^[5]
• To aid public acceptance, an exhaust system was designed to catch and filter the radioactive tritium the fusion process produces.^[6]

See also

• Fusion reactor
• National Institutes of Natural Sciences, Japan