Modelling resistive wall modes with self-consistent inclusion of drift kinetic resonances

The resistive wall mode instability limits the achievable plasma pressure in present and future advanced tokamak scenarios. We investigate the effect of drift kinetic resonance damping, due to plasma thermal particles, on the stability of this mode. A self-consistent toroidal kinetic damping model is developed and incorporated into the MHD code, MARS-F. The new code (MARS-K) allows study of the kinetic effects in both a perturbative and non-perturbative manner. The primary difference between these two approaches is that the former normally uses the no-wall ideal kink eigenmode structure to compute the kinetic energy perturbation, whilst the latter takes into account self-consistently the modification of the RWM eigenfunction by the kinetic effects. The perturbative approach in MARS-K is benchmarked against another, also perturbative calculation using the ideal MHD code MISHKA and the drift-orbit particle-following code HAGIS. The perturbative approach normally predicts a significant modification of the perturbed total energy (fluid + vacuum + wall + drift kinetic) by the kinetic contribution, which in many cases leads to a complete stabilization of the mode. However, the non-perturbative approach in many cases studied results in a partial stabilization, due to the fact that the drift kinetic energy is sensitive to the mode structure, that is modified by the kinetic effects. Therefore, the predicted RWM stability can be significantly different, depending on whether the kinetic terms are included self-consistently. Detailed comparison of the self-consistent modelling with the experimental results (JET and DIII-D) is in progress. Predictive simulations of the RWM stability will be made for the ITER advanced plasmas, using the new damping model. (author)