;Plasma heating : Because the stellarator lacks the tokamak's plasma current as a form of heating, heating the plasma is accomplished with external devices.
32.
The Helically Symmetric Experiment ( HSX ) at the University of Wisconsin-Madison is such a quasi-helically symmetric stellarator ( helical axis of symmetry ).
33.
More recently, in the 1990s, problems with the tokamak concept have led to renewed interest in the stellarator design, and a number of new devices have been built.
34.
Some important modern stellarator experiments are Wendelstein 7-X in Germany, the Helically Symmetric Experiment ( HSX ) in the USA, and the Large Helical Device in Japan.
35.
With plasma discharges lasting up to 30 minutes, Wendelstein 7-X will try to demonstrate the essential stellarator attribute : continuous operation of a high-temperature hydrogen plasma.
36.
Stuhlinger followed this by a visit with Van Allen at his home in Princeton, New Jersey, where Van Allen was on sabbatical leave from Iowa to work on stellarator design.
37.
This was similar to the stellarator approach in concept, and although it would have lower field strength than those machines, the energy needed to maintain the confinement was much lower.
38.
As a result, the stellarator is not perfect in terms of canceling out the drift, but the net result is to so greatly reduce drift that long confinement times appeared possible.
39.
As currents were ramped up during the 1980s it appeared that they might represent a serious problem to further improvements in confinement, and the all-magnetic stellarator designs saw renewed interest.
40.
Spitzer read the articles during his trip to plasma in a toroid pointed out by Enrico Fermi, while riding the ski lift he hit upon the solution now known as the stellarator.
