On modeling the interaction of neoclassical and classical tearing modes with rf waves

A model which incorporates the effects of electron cyclotron current drive (ECCD) into the magnetohydrodynamic (MHD) equations is implemented in the NIMROD code [C. R. Sovinec et al., J. Comp. Phys. 195, 355 (2004)] and used to investigate the effect of ECCD injection on the stability, growth, and dynamical behavior of magnetic islands associated with resistive tearing modes. Predictions of the model are shown to quantitatively and qualitatively agree with numerical results obtained from the inclusion of localized ECCD deposition in static equilibrium solvers. The complete suppression of the (2, 1) resistive tearing mode by ECCD is demonstrated. Consequences of the shifting of the mode rational surface in response to the injected current are explored, as are the consequences of spatial ECCD misalignment. We discuss the relevance of this work to the development of more comprehensive predictive models (in support of existing/future experiments, e.g. ITER) for ECCD–based mitigation and control of neoclassical tearing modes.