Fluctuation and transport reduction by current profile control in MST

Summary form only given. The dominant energy loss mechanism in the reversed field pinch (RFP) results from parallel streaming in a stochastic magnetic field. This stochasticity results from B~/B/spl sim/1% magnetic fluctuations which accompany m=1, n/spl sim/2R/a tearing (or resistive kink) instabilities in the plasma core. Inductive, electrostatic, and RF current drive are being explored as techniques to reduce the tearing fluctuation and the associated energy loss. For example, by applying an auxiliary poloidal inductive electric field to the MST RFP plasma, the current density gradient is reduced, the growth of the m=1 tearing fluctuations slows, and the energy confinement time doubles. Sawteeth associated with the m=1 instabilities are also suppressed. Since a toroidal flux change linking the plasma is required, inductive current drive must be transient to avoid excessive perturbation of the equilibrium, To sustain and enhance the improved plasma, electrostatic and RF current drivers are being developed. The novel electrostatic current drive scheme utilizes a plasma source for electron injection.