Interaction of an external rotating magnetic field with the tearing mode in a plasma surrounded by a resistive wall

The nonlinear dynamics of a tearing mode interacting with an externally applied rotating field and a resistive wall is studied. A pair of coupled equations describing the evolution of the amplitude and frequency of a single tearing mode is derived and used in this study. The equations are valid for both tokamaks and reversed field pinches (RFP). Numerical analysis is applied on the RFP configuration. Bifurcated stationary states of the tearing mode are found. Transition between these stationary states is studied by time dependent integration. This investigation shows that the dynamics of the tearing mode is substantially affected by the external applied field. For example, a tearing mode locked to the resistive wall can be unlocked to rotate with the external field; the required amplitude and frequency of the external field are presented. Finally, the possibility of utilizing the external resonant magnetic field to enhance the amplitude of an unlocked single helicity state in the RFP is discussed. (C) 2001 American Institute of Physics.