US-European transport task force Workshop, 6-9 de Abril de 2005, Napa, USA

	Recent Progress in Diagnostics of Energetic Particle Driven Modes: New Opportunities and Challenges
	S. Sharapov, B. Alper, H. Berk, D. Borba, C. Boswell, B. Breizman, E. de la Luna, J. Fessey, S. Hacquin, G. Kramer, R. Nazikian, S. Pinches, J. Rapp, D. Testa, N. Young e os contributos JET-EFDA
	Resumo
	The physics of highly energetic ions in tokamaks is one of the most important issues for experimental study on JET and on spherical tokamak MAST. The high plasma currents of these tokamaks, together with ICRH and NBI systems on JET and super-Alfvénic NBI on MAST give these machines unique possibilities in fast particle research, with a particularly strong position for studying instabilities of Alfvén eigenmodes (AEs). Recently, these possibilities have been enhanced further by the development of several new diagnostic techniques, among which the most significant are: · Interferometry diagnostics for detecting AEs on JET [1], and · Spectroscopic determination of TAE amplitude from the sweeping rate of TAE frequency on MAST [2]. The new diagnostic techniques have opened up new opportunities for MHD spectroscopy based on the detection of Alfvén instabilities excited by fast ions. They also lead to a number of challenges confronting the theory of Alfvén instabilities. On JET, the interferometry detection of Alfvén cascades (ACs) significantly improved accuracy of measurements of temporal evolution of q (t ) min [1] needed to determine the optimum time for the application of the main heating to trigger internal transport barriers in advanced plasmas. Some JET discharges have also revealed excitation of ACs by sub-Alfvénic NBI-produced ions, and this observation was also made on DIII-D and JT-60U [3]. This poses a question on determining a beam velocity threshold required for driving the modes and whether such modes could explain some anomalies in the beam relaxation observed earlier on DIII-D. On MAST, the observation and interpretation [2] of the sweeping-frequency TAE has validated the existence of “hole-clump” pairs (nonlinear Bernstein-Green-Kruskal-type long-living fluctuations) on the fast ion distribution function in accordance with theory [4]. Such development point to a new way of determining the internal mode amplitude based on external measurements alone. Alternatively, the rate of TAE-frequency sweeping deviating from that predicted by [4], poses a question of more accurate description of “hole-clump” pairs, while the use of a similar technique for “chirping” modes on MAST, and for n = 0 frequency-sweeping modes on JET represents a new challenging problem. This work was performed partly under EFDA and partly funded by Euratom and the UK EPSRC. [1] S.E. Sharapov et al, Physical Review Letters 93 165001 (2004) [2] S.D. Pinches et al, Plasma Physics Controlled Fusion 46 S47 (2004) [3] R. Nazikian et al., 20th IAEA Fusion Energy Conference, IAEA-CN-116/EX/5-1 (2004) [4] H.L. Berk, B.N. Breizman, N.V. Petviashvili, Physics Letters A 238 408 (1998)