Influence of radio frequency waves on the interchange stability in HANBIT mirror plasmas

Experimental and theoretical studies are made of the influence of high frequency radio frequency (rf) waves upon interchange stability in HANBIT mirror plasmas. An emphasis is put on the interchange stability near the resonance region, ω0≈Ωi, where ω0 is the angular frequency of the applied rf wave and Ωi is the ion cyclotron frequency. Recent HANBIT experiments have shown the existence of the interchange-stable operation window in favor of ω0/Ωi ≤1 with its sensitivity on the applied rf power. A strong nonlinear interaction between the rf wave and the interchange mode has been observed with the generation of sideband waves. A theoretical analysis including both the ponderomotive force and the nonlinear sideband wave coupling has been developed and applied to the interpretation of the experiments, resulting in a good agreement. From the study, it is concluded that the nonlinear wave-wave coupling process is responsible for the rf stabilization of the interchange modes in HANBIT mirror plasmas operating near the resonance condition.