Fast-ion transport and toroidal rotation response to externally applied magnetic perturbations at the ASDEX Upgrade tokamak

Abstract

This paper studies the effect of 3D magnetic perturbations on fast-ion confinement, and its impact on the toroidal rotation velocity profile. Two low collisionality H-mode experiments carried out at the ASDEX Upgrade tokamak have been analyzed. The two discharges feature different magnetic field helicity (q95), and differences in the velocity-space and level of fast-ion losses are observed. A new analysis technique has been developed that sheds light on the dependencies between fast-ion losses and toroidal rotation, providing for the first time correlation patterns resolved in radius and velocity space of the lost fast-ions. The correlation intensifies towards the plasma edge and is strongly dependent on the orbit topology of the lost fast-ions. The ASCOT orbit following code has been used to characterize the fast-ion resonant transport and beam driven torques, using the vacuum approach and including plasma response. The change of the toroidal canonical momentum, which serves as figure of merit for resonant fast-ion transport, has been calculated with ASCOT. The beam geometry and q95 are found to have a strong impact on the fast-ion transport and losses. The fast-ion transport induced by the magnetic perturbations affects the beam driven torques. The effect of the changes of the jxB and collisional torques on plasma rotation is analyzed using the torques simulated by ASCOT and simple momentum balance calculations. For the low q95 = 3.8 discharge, which benefits from a resonant amplification, we find excellent agreement with the measured variation of the toroidal velocity. For the high q95 = 5.5 discharge, the inclusion of the plasma response improves the comparison with experimental data with respect to the vacuum estimation, but still some differences with experiments are observed. This suggests that other non-resonant effects could play a role for the determination of the toroidal rotation profile.

Effects of external kink and fishbone-like modes on energetic particle transport in tokamak plasmas

“…Extensive investigations have been reported in literatures on the effects of various three-dimensional (3D) perturbations on EP transport and loss. These perturbations include those due to the internal kink mode [30][31][32], the fishbone mode [33][34][35][36][37], various Alfvén eigenmodes [38][39][40][41][42], and the external resonant magnetic perturbations [43][44][45][46][47][48][49]. Much fewer studies have been carried out on the influence of the XK or FLM instabilities on EP confinement.…”