(IC/P4-2) Formation and Sustainment of Field-reversed Configuration by Rotating Magnetic Field with Spatial High-harmonic Components

M. Inomoto1), K. Yambe1), K. Kitano1), S. Okada1)
1) Center for Atomic and Molecular Technologies, Osaka University, Osaka, Japan

Abstract.  Rotating magnetic field (RMF) is one of the most successful current-drive methods for high-beta field-reversed configuration (FRC) plasmas. A novel RMF method using spatial high-harmonic components has been proposed and experimentally investigated in the FRC injection experiment (FIX) in order to resolve the problem that the dipole RMF might open up the closed surface of the FRC and connect the bulk plasma to the vessel wall. The RMF generated by the antennas located inside a conducting vacuum vessel contains large spatial high-harmonic components, whose rotation frequency is slower and sometimes in the reverse direction compared to the fundamental component of the RMF. Since the electrons in the bulk FRC plasma are expected to rotate synchronously with the fundamental component of the RMF, the high-harmonic components will be absolutely excluded at the plasma edge, resulting in a generation of effective magnetic pressure near the separatrix, which helps to keep the separatrix away from the vessel wall. The proposed high-harmonic RMF method will be helpful in reducing the particle loss and thermal load when applied to the fusion core plasma. Experimental results show that the FRC plasma sustained by the high-harmonic RMF has steep density gradient at r∼0.18 - 0.25 m provided by magnetic pressure of excluded high-harmonic components of the RMF, which successfully keeps the separatrix away from the chamber wall at r = 0.4 m. The time-independent FRC equilibrium is also observed to show azimuthal deformation as predicted from the one-dimensional model of the RMF-FRC equilibrium, nevertheless, the experimental results rarely show severe degradation of the plasma including rotational instability. The azimuthal deformation of the FRC plasma sustained by the high-harmonic RMF might essentially eliminate the destructive modes caused by the rotation of the plasma column due to electron-ion collisions or some other reasons.

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