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Published on Nov 13, 2007
A view inside Japan's Large Helical Device (LHD) by the National Institute for Fusion Science, Nagoya.
The LHD is a stellarator which works slightly different to a tokamak. The plasma in a tokamak requires two magnet fields, the poloidal and toroidal fields. The poloidal field squashes the plasma as it flows around the torus (this is called the pinch effect) and is generated by an internal current within the plasma induced by transformer action. The toroidal field stop the plasma from snaking about and is provided by large external magnets surrounding the torus. In the stellarator, both the poloidal and toroidal magnetic field is generated by external helical coils (magnet coils that snake around the torus) and no plasma current is required. The absence of a plasma current gives stellarators a potentially significant advantage over tokamaks as fusion power plants (there would be no disruptions, no current drive and no stability control system). In general though, stellarators have not been as successful as tokamaks but a considerable level of research continues, notably in Germany, Spain, USA, Russia and Japan. Stellarator news- http://www.ornl.gov/sci/fed/stelnews/ More info- http://en.wikipedia.org/wiki/Stellarator