Nonlinear dynamics of the reversed field pinch: Torques, dynamo, and reconnection

The magnetic field configuration of the Reversed-Field Pinch (RFP) typically exhibits resistive tearing modes of poloidal mode number m=1 resonant in the plasma core and m=0 resonant in the plasma edge. In the Madison Symmetric Torus (MST) RFP, these fluctuations cause electromagnetic torques which alter the flow profile, and magnetic reconnection and dynamo effects which alter the magnetic configuration and current density profile. Described in this paper are three key physics results: 1) The discovery of internal electromagnetic torques between two core modes, a three-wave interaction requiring the mediation of the m=0, n=1 mode at the plasma edge. 2) Direct measurements of the parallel dynamo at the plasma edge confirm that it balances Ohm's law and is primarily driven by the m=0 mode. 3) Measurements across the reconnection layer at the q=0 resonant surface demonstrate the dominance of m=0 current density fluctuations in the vicinity of this resonant surface and show a phase flip of the radial plasma flow velocity fluctuations across the resonant surface. (author)