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{{Infobox fusion devices
|name                 = LHD
|fullname             = Large Helical Device
|image                = Large Helical Device 2014.jpg
|imagetitle           = The Large Helical Device in 2014
|type                 = [[Heliotron]]
|city                 = [[Toki, Gifu|Toki]]
|state                = 
|country              = [[Japan]]
|coordinates          = <!-- {{coord|latitude|longitude|type:city|display=inline,title}} -->
|affiliation          = [[National Institutes of Natural Sciences, Japan|National Institute for Fusion Science]]
|major_radius         = {{cvt|3.9|m}}
|minor_radius         = {{cvt|0.6|m}}
|volume               = 
|field                = {{cvt|3.0|T}}
|heating              = 
|power                = 
|time                 = 
|current              = 
|construction_date    = 
|operation_start_year = 1998
|operation_end_year   = 
|ongoing              = yes
|prev                 = 
|next                 = 
|related              = 
|website              = <!-- {{url|insert here}} -->
|other_links          = 
}}
The {{Nihongo|'''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 Institutes of Natural Sciences, Japan|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.

[[File:LHD plasma vacuum vessel.jpg|thumb|300px|An interior view of the vacuum vessel, which shows the LHD's superconducting coils.]]

The objective of the project is to conduct [[nuclear fusion|fusion]] [[Plasma (physics)|plasma]] confinement research in a steady state in order to elucidate possible solutions to physics and engineering problems in [[Helix|helical]] [[fusion power|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 [[tokamak]]s. 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.<ref>{{cite journal | last1 = Morisaki | first1 = T | last2 = Masuzaki | first2 = S | display-authors = 1 | title = Initial experiments towards edge plasma control with a closed helical divertor in LHD | journal = Nucl. Fusion | volume = 53 | pages = 063014 | date = 2013 | issue = 6 | url = https://iopscience.iop.org/article/10.1088/0029-5515/53/6/063014 | doi = 10.1088/0029-5515/53/6/063014 | bibcode = 2013NucFu..53f3014M | s2cid = 122537627 | url-access = subscription }}</ref><ref>{{cite web |url=https://www.jspf.or.jp/jspf_annual2018/JSPF35/pdf/S8-4.pdf  |title=Progress in Divertor and Edge Transport Research for Stellarator Plasmas |date=December 6, 2018 |first1=Aaron |last1=Bader |first2=Florian |last2=Effenberg|first3=Chris C. |last3=Hegna |archive-url=https://web.archive.org/web/20230726233025/www.jspf.or.jp/jspf_annual2018/JSPF35/pdf/S8-4.pdf |archive-date=2023-07-26}}</ref>

==History==
* Design finalized 1987
* Start of construction 1990
* Plasma operations from 1998
* Neutral beam injection of 3 MW was used in 1999.<ref>{{cite journal |title=Plasma confinement studies in LHD |journal=Nuclear Fusion |volume=39 |issue=11Y |pages=1659–1666 |year=1999 |quote=Heating by NBI of 3 MW produced plasmas with a fusion triple product of 8 × 10<sup>18</sup>m<sup>−3</sup> 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 × 10<sup>19</sup> m<sup>−3</sup> |doi=10.1088/0029-5515/39/11Y/305 |last1=Fujiwara |first1=M. |last2=Yamada |first2=H. |last3=Ejiri |first3=A. |last4=Emoto |first4=M. |last5=Funaba |first5=H. |last6=Goto |first6=M. |last7=Ida |first7=K. |last8=Idei |first8=H. |last9=Inagaki |first9=S. |last10=Kado |first10=S. |last11=Kaneko |first11=O. |last12=Kawahata |first12=K. |last13=Kobuchi |first13=T. |last14=Komori |first14=A. |last15=Kubo |first15=S. |last16=Kumazawa |first16=R. |last17=Masuzaki |first17=S. |last18=Minami |first18=T. |last19=Miyazawa |first19=J. |last20=Morisaki |first20=T. |last21=Morita |first21=S. |last22=Murakami |first22=S. |last23=Muto |first23=S. |last24=Mutoh |first24=T. |last25=Nagayama |first25=Y. |last26=Nakamura |first26=Y. |last27=Nakanishi |first27=H. |last28=Narihara |first28=K. |last29=Nishimura |first29=K. |last30=Noda |first30=N. |bibcode=1999NucFu..39.1659F |s2cid=250824691 |display-authors=29 }}</ref>
* In 2005 it maintained a plasma for 3,900 seconds.<ref>[http://iopscience.iop.org/article/10.1088/1742-6596/25/1/024 ''Achievement of One Hour Discharge with ECH on LHD'' 2005]</ref>
* 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.<ref>{{Cite journal|last=Hamaguchi, Imagawa, Obana, Yanagi and Mito|date=2018|title=Operations of the Helium Subcooling System for the LHD HelicalCoils during Ten Plasma Experimental Campaigns|url=http://www.jspf.or.jp/PFR/PDF2018/pfr2018_13-3405057|journal=Plasma and Fusion Research|volume=13|pages=3405057|doi=10.1585/pfr.13.3405057|bibcode=2018PFR....1305057H |doi-access=free}}</ref>
* To aid public acceptance, an exhaust system was designed to catch and filter the radioactive [[tritium]] the fusion process produces.<ref>{{Cite web|url=https://www.researchgate.net/publication/322866554|title=Design and commissioning of the exhaust detritiation system for the Large Helical Device|website=ResearchGate|language=en|access-date=2019-03-04}}</ref>
{{expand section|date=March 2018}}

==See also==
* [[Fusion reactor]]
* [[National Institutes of Natural Sciences, Japan]]

==References==
{{reflist}}

==External links==
* [https://www-lhd.nifs.ac.jp/pub/index_e.html ''Large Helical Device'' Website]
* [http://ncsx.pppl.gov/Physics/NSTT/Harris_Jan08r3.pdf Super Dense Core plasmas in LHD. Harris. 2008] 16 slides. advanced - inc ballooning mode and future development options

{{fusion experiments}}

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[[Category:Fusion power]]
[[Category:Stellarators]]
[[Category:Plasma physics facilities]]
[[Category:Toki, Gifu]]