ABSTRACT
New features of instabilities driven by energetic ions are revealed. It is found that these instabilities can affect plasma heating and rotation by channeling the energy and momentum of the energetic ions to the region where the destabilized waves are damped. Because of the energy channeling, the plasma core may not be heated by the energetic ions even when these ions have a very peaked radial distribution. It is likely that this new phenomenon can explain experiments on the spherical torus NSTX where a broadening of the temperature profile and even a drop of the temperature at the plasma center with increasing injected power were observed during Alfvén instabilities [D. Stutman, Phys. Rev. Lett. 102, 115002 (2009)10.1103/PhysRevLett.102.115002]. The momentum channeling can lead to plasma rotation and frequency chirping due to the Doppler shift varying in time.
ABSTRACT
Enhanced plasma heat conductivity in the presence of kinetic Alfvén waves (KAW) is predicted theoretically. The enhancement is shown to be strongest when the electron collision frequency exceeds the particle transit frequency in the wave field. Alfvén waves (both KAW and ideal MHD Alfvén eigenmodes generating the KAW) are studied in a shot of the Wendelstein 7-AS stellarator. On the basis of these results, strong thermal crashes observed during bursting Alfvénic activity in the mentioned shot are explained.
