Partial current drive by a fast magnetosonic wave in reversed filed pinch plasma

A single-ray fast magnetosonic wave is used to drive current with strong absorption in a reversed field pinch, in conjunction with the usual ohmic current. Using a driven current smaller than the ohmic current, by an order of magnitude the converged field configurations approach Taylor's minimum energy state. The driven current profile is affected by the local beta value profile, which plays the role of broadening the driven current profile. Increasing the wave phase speed modifies the current density profile in the central region with a high driving efficiency so that it approaches the on-axis current peak profile, resulting in tearing mode stability. A sufficiently large poloidal driven current in the outer region reverses the toroidal field and would eliminate or reduce the need for dynamo action within the plasma. These favourable tendencies for both the approach to the minimum energy state and the field reversal become stronger as the wave phase speed decreases and the beta value increases. In conclusion, a proper selection of the wave power spectrum over the entire plasma region, which depends on the plasma beta value, is required to improve the plasma stability and the energy confinement time. Significant wave damping due to higher harmonic ion cyclotron resonances is observed for faster waves in higher beta plasmas. (author). 22 refs, 18 figs, 1 tab