Modeling sawtooth stabilization by energetic ions from neutral beam injection

Recent advances in modeling the effects of anisotropic energetic ion distributions have enabled the development of a complete coherent physics explanation of sawtooth stabilization in both conventional and spherical tokamaks. As an example, a complete model has been developed to explain the asymmetric stabilization of sawteeth with respect to neutral beam injection direction in the Joint European Torus. This asymmetric sawtooth stabilization [M. Nave , Phys. Plasmas 13, 014503 (2006)] arises because of both the destabilizing contribution from the counterpassing ions and the strong modification of the stabilizing contribution of the nonadiabatic trapped ions due to flow shear. The fast particle effects including pressure anisotropy, sheared flows, and the adiabatic response to the internal kink mode have been modeled in general toroidal geometry for the first time.