A detailed study of kinetic effects of energetic particles on resistive MHD linear stability

摘要

The effects of energetic particles on MHD instabilities is a key issue in the basic physics that will be important in burning plasma experiments such as ITER. Recently, experiments (JET. JT-60U and DIII-D) have shown that the kinetic effects of energetic particles can play a crucial role in the stability of the m = 2/1 tearing mode, where the fraction of energetic particle β_(frac) = β_h/β is high (β = 2_(μ0)P/B~2, P is pressure, B is magnetic field and βh is the energetic particle β). For the study of the kinetic effects of energetic particles on resistive MHD stability, using model equilibria based on DIII-D experimental reconstructions, the non-ideal MHD linear stability of cases unstable to the 2/1 mode is investigated including a δf PIC model for the energetic particles coupled to the nonlinear 3D resistive MHD code NIMROD (Kim et al 2008 Phys. Plasmas 15 072507). The growth of unstable modes is calculated at a series of β, β_(frac) and S = tr/ta (the ratio of the resistive time to Alfven time), spanning from the resistive to the ideal unstable regime of the mode, up to and above β_(frac) - 0.25, and well into the asymptotic regime of the resistivity. It is observed that energetic particles have significant damping and stabilizing effects at experimentally relevant β, β_(frac) and 5, and less damping and stabilizing effects at the ideal unstable regime. It is also observed that energetic particles excite a real frequency of the 2/1 mode. The growth rates significantly reduce at experimentally relevant β, β_(frac) and S due to the mode interacting with the trapped particles and 'barely passing' particles. Furthermore, extrapolation of the results is discussed for implications for JET and ITER, where the effects are projected to be significant.