Fusion Science and Technology / Volume 51 / Number 1 / January 2007 / Pages 122-128
Technical Paper / Stellarators
Toroidal current has been studied in electron cyclotron heating (ECH) and ECH + neutral beam injection (NBI) plasmas on Heliotron J by controlling the bumpy field component. In the ECH plasma with high density, the toroidal current increases from 0.3 to 1.5 kA when B04/B00 is increased from 0.01 to 0.15, where B04 and B00 are the bumpy field and the uniform field components, respectively. The observed toroidal current is qualitatively in good agreement with neoclassical calculation results without radial electric field except for a low bumpy configuration case at low density. If the radial electric field is responsible for the deviation in the low bumpiness case, the central electric potential is estimated to be ~3 to 5 kV. The dependence of the net toroidal current on the bumpiness has also been observed in the ECH + NBI plasma. An estimation of the Ohkawa current has been attempted.