21st Fusion Energy Conference, 13-21 de Outubro, Chengdu, China

	Interpretation of Mode Frequency Sweeping in JET and NSTX
	P. Martin , W. Bobkov, G. Conway, U. Fahrbach, A. Flaws, M. Garcia Muñoz, M. Gobbin, S. Graça, S. Günter, V. Igochine, K. Lackner, M. Maraschek, L. Marrelli, P. Piovesan, K. Sassenberg, E. Strumberger, W. Suttrop, H. Zohm a Equipa ASDEX-Upgrade e o AUG ICRF Group
	Resumo
	Rapid spontaneous frequency sweeping has been observed in many different fusion related plasma physics experiments [1 – 7] for such modes as the Fishbone, TAE and Hot Electron Interchange Mode. This phenomenon been attributed to the formation of phase space structures, that together with plasma dissipation from the background plasma, forces the frequency to sweep [8-11]. These phase space structures take the form of holes and clumps where the distribution function of the holes (clumps) is lower (higher) than the ambient background distribution surrounding these structures in phase space. The sharp phase space gradient is maintained by wave trapping of particles trapped by a finite amplitude wave. A quantitative description of this process is described in [11] for the bump-ontail instability. The theory was extended to the TAE mode in [12] and a theoretical outline of the general case valid for waves in nearly any configuration is given in [13]. The frequency sweeping of modes is expected to take place near the marginal conditions for the onset of instability, when there is a balance between dissipation mechanisms and the kinetic drive from fast particles. Frequency sweeping may facilitate the overlap of Alfvénic modes that can lead to undesirable global transport of alpha particles in a burning plasma. Here we shall also speculate how frequency sweeping may prevent parasitic alpha particle loss. Hence, it is of intrinsic interest for fusion confinement to thoroughly understand the frequency sweeping process.