
Author(s):
Y. Nakamura et al.

Title:
Analysis of Net Plasma Currents in NonAxisymmetric Plasmas
Date of publication:
Oct. 2006

Key words:
21 IAEA Fusion Energy Conference, TH/P71

Abstract:
Net plasma currents and those time evolutions are studied numerically for nonaxisymmetric plasmas. Based on the neoclassical transport theory, effects of the nonaxisymmetry on the bootstrap (BS) current are investigated for a tokamak plasma which has toroidal field (TF) ripples. It is found that the BS current is reduced by a factor of a square root of the TF ripple ratio in a rippled tokamak. We also found that the reduction of the BS current due to TF ripples becomes small if we take the poloidal dependence of the TF ripple ratio into account. For helical plasmas, we have developed a net plasma current simulation code for integrated simulations, and analyze net plasma currents observed in a Large Helical Device (LHD) plasma. It is found that noninductive currents can be sufficiently large to change the rotational transform profile at the plasma core region, even though the total current is too small to change the rotational transform at the plasma boundary. The effect of the inductive current is important for estimation of the net plasma current especially when the beam driven currents are considered.

