Simulation study of the dynamo structure in the reversed-field pinch

The dynamo structure in the reversed-field pinch (RFP) is studied through the nonlinear dynamics of a single-helicity mode. Simulation is concentrated upon the physical structure of nonlinear interactions of the plasma flow and magnetic fluctuation. The result indicates that when the initial equilibrium profile is deformed by resistive diffusion, the radial flow is driven near the core of the plasma. As this flow forms a vortex structure and magnetic fluctuation grows radially, the dynamo electric field is helically induced just inside the reversal surface and then the toroidal flux is increased. This dynamo electric field correlates to the nonlinear evolution of the kinetic energy of the m=1 mode, and the increase of the toroidal flux originates in the growth process of the magnetic energy of this mode. Consequently, the RFP configuration can be sustained by the single-helicity evolution of the m=1 mode alone, and the electric field induced by the interactions of the toroidal velocity and the radial magnetic field is the most dominant source on the dynamo action