PARTIAL CURRENT DRIVE BY A FAST MAGNETOSONIC WAVE IN REVERSED-FIELD PINCH PLASMA

A single-ray fast magnetosonic wave is used to drive current with stro ng 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 th e driven current profile. Increasing the wave phase speed modifies the current density profile in the central region with a high driving eff iciency so that it approaches the on-axis current peak profile, result ing in tearing mode stability. A sufficiently large poloidal driven cu rrent in the outer region reverses the toroidal field and would elimin ate or reduce the need for dynamo action within the plasma. These favo urable tendencies for both the approach to the minimum energy state an d the field reversal become stronger as the wave phase speed decreases and the beta value increases. In conclusion, a proper selection of th e 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 h armonic ion cyclotron resonances is observed for faster waves in highe r beta plasmas.