Radial dependence of parametric instability due to magnetic perturbation: a scenario for ELM control

The stability of the tokamak edge pedestal to the ballooning-kink mode is examined in the presence of the applied stochastic field lines using the four-wave parametric process. It is shown that the H-mode (high confinement mode) edge pedestal is unstable to the ideal ballooning mode in the absence of the applied stochastic fields. It is also shown that in the presence of the kink effect, dominated by the bootstrap current, the ballooning mode is more virulent. The modes are suppressed if the applied magnetic field perturbation amplitude is larger than. The instability driven due to small dissipation, which may be a possible candidate for transport in the pedestal region, is unaffected by these applied fields. Hence we expect no change in the edge pedestal confinement. We have opposing results in the outer edge region where the density and the temperature profiles are flattened. These results are consistent with the observations by Evans et al¹.

1. T. E. Evans, R. A. Moyer, P. R. Thomas et al., Phys. Rev. Lett. 92, 235003 (2004)