Nonlinear Study of Error Field Effects in NSTX

RWM stabilization by plasma rotation in NSTX is impeded by the presence of a time-dependent non-axisymmetric component to the toroidal field [1]. Confinement is improved by active correction of this error field; its exact cause is still under investigation. A numerical study of the effects of the error field on magnetic island formation was conducted with ideal linear codes [2], providing estimates of the island widths based on the amplitudes of the singular current sheets that result from the perturbation. We extend these results by conducting nonlinear, non-ideal studies of these effects using the M3D code [3]. The nonlinear correction to the linear response to a pure m=2, n=1 perturbation is shown, followed by investigations of the effects of toroidal rotation and of mode locking and consequent rotation damping. \newline [1] J.E. Menard, et al., submitted to Nucl. Fus., 2007. \newline [2] J.K. Park, poster presented at Sherwood Fusion Theory Conference, Annapolis, MD, April 2007. \newline [3] W. Park, et al., Phys. Plasmas 6, 1796 (1999).