(TH/3-2) Electron fishbones: theory and experimental evidence

F. Zonca1), P. Buratti1), A. Cardinali1), L. Chen2), J.-Q. Dong3), Y.-X. Long4), A. Milovanov 1)5)6), F. Romanelli1), P. Smeulders1), L. Wang3), Z.-T. Wang3)
1) Associazione EURATOM-ENEA sulla Fusione, Frascati, Italy
2) Dept. of Physics and Astronomy, Univ. of California, Irvine CA 92697-4575, U.S.A.
3) Southwestern Institute of Physics, P.O. Box 432, Chengdu 610041, P.R.C.
4) Institute of Physics, Chinese Academy of Sciences, Beijing 100080, P.R.C.
5) Department of Physics and Technology, University of Tromsų, N-9037 Tromsų, Norway
6) Space Research Institute, Russian Academy of Sciences, Moscow, Russia

Abstract.  We discuss the processes underlying the excitation of fishbone-like internal kink instabilities driven by supra-thermal electrons generated experimentally by different means: Electron Cyclotron Resonance Heating (ECRH) and by Lower Hybrid (LH) power injection. The peculiarity and interest of exciting these electron fishbones by ECRH only or by LH only is also analyzed. Not only the mode stability is explained, but also the transition between steady state nonlinear oscillations to bursting (almost regular) pulsations, as observed in FTU, is interpreted in terms of the LH power input. These results are directly relevant to the investigation of trapped alpha particle interactions with low-frequency MHD modes in burning plasmas: in fact, alpha particles in reactor relevant conditions are characterized by small dimensionless orbits, similarly to electrons; the trapped particle bounce averaged dynamics, meanwhile, depends on energy and not mass.

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