Analytical Studies on the Nonlinear Oscillation Due to an m=1 Non-Resonant Current-Driven Mode in RFP Plasmas

Abstract

Analytical studies are presented on the nonlinear oscillation due to a single non-resonant current-driven mode with poloidal mode number of m=1 in the vicinity of a marginally stable state in RFP plasmas. A perturbation expansion with respect to the difference of the toroidal wave number from one at the marginally stable state is used togather with the multiple-time-scale method. The system of equations governing the time development of the amplitude of the m=1 mode is obtained, which indicates that the nonlinear oscillation is possible in RFP plasmas with a relatively high S number (S\gtrsim10⁴) and that the oscillation is interpreted as an amplitude oscillation of the m=1 mode. The analytical results by using the perturbation theory well explain those of the numerical simulation.