Analysis and Control of Spontaneous Currents in Rippled Tokamak Plasmas and Helical Plasmas

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In magnetically confined toroidal plasmas with high plasma pressure, a spontaneous current, which called the bootstrap current, flows as is predicted by the neoclassical transport theory, and it gives an significant influence on the plasma confinement. The following studies have been done in order to investigate the effects of the bootstrap current on the plasma confinement theoretically, and to consider the methods to control the bootstrap current.1. Three dimensional MHD equilibrium code, HINT2, has been developed to calculate the MHD equilibrium of non-axisymmetric plasmas accurately. We also analyze the effect of the bumpy component of the plasma boundary shape on the MHD stability.2. In the experiments of an L=1 heliotron device, Heliotron J, it is demonstrated that the direction of the bootstrap current can be reversed when the magnetic configuration is varied. We did the theoretical analysis of the bootstrap current in L=1 heliotron plasmas and in rippled tokamak plasmas, and clarified the dependence of the magnetic configuration and the toroidal field ripple on the bootstrap current.3. The integrated simulations of the plasma current profile including the beam driven current and the bootstrap current have been done with the consistent MHD equilibrium calculation. For this purpose, numerical program which analyze the bootstrap current and beam driven current has been modularized, and the module which simulate the time evolution of the plasma current profile in non-axisymmetric toroidal plasmas has been developed. We clarified the mechanism of the transient response of the plasma current profile in LHD plasma experiments.