Dependence of Toroidal Current on Bumpy Field Component in Heliotron J

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.