Interaction of fast particles with neoclassical tearing modes

• Published in: Physics of plasmas 2000-03, Vol.7 (3), p.935-939
• Main Authors: Sesnic, S., Günter, S., Gude, A., Maraschek, M.
• Format: Article
• Language: English
• ISSN: 1070-664X; 1089-7674
• DOI: 10.1063/1.873891

Fast particle driven m=1/n=1 modes in the form of fishbones frequently initiate neoclassical tearing modes (NTMs) on Axisymmetric Divertor Experiment Upgrade [W. Köppendörfer et al., 14th International Conference on Plasma Physics and Controlled Fusion (International Atomic Energy Agency, Vienna, 1993), Vol. I, p. 127] and other neutral-beam-injection heated tokamaks, but disappear after the NTMs have reached a quasistationary state. A burst of other magnetohydrodynamic phenomena, described in this paper, appear instead, similar in repetition rate and time signature of frequency and amplitude. They are associated with the growth of the m=2/n=2 satellite of the m=3/n=2 neoclassical tearing mode, and a transient increase (termed FJ=frequency jump event ) in the rotation frequency of the coupled mode system. They lead to a thermal crash, originating at q=3/2, propagating inwards up to the q=1 surface. With a lower repetition rate (more characteristic of sawteeth) similar events occur, where a large 1/1 component also appears and the fast crash propagates to the plasma center frequency jump with sawtooth character (FJST). The analogies to the fishbone case suggest that this phenomenon is caused by the interaction with fast particles, which transiently impress their precession frequency on the pre-existing magnetic perturbation of the NTM.