Non-linear Dynamics Of Toroidicity-induced Alfven Eigenmodes On The National Spherical Torus Experiment

Podesta, M. ; Crocker, N. A. ; Fredrickson, E. D. ; Gorelenkov, N. N. ; Heidbrink, W. W. ; Kubota, S. ; LeBlanc, B. P.

Princeton University. Plasma Physics Laboratory.

关键词: Beam Injection;    Heating;    Amplitudes;    Transport Oscillations, Nonlinear, Mode Coupling, Tokamaks, Nstx, Spherical Torus;    70 Plasma Physics And Fusion Technology;   

DOI  :  10.2172/1013043
RP-ID  :  PPPL-4614
RP-ID  :  DE-ACO2-09CH11466
RP-ID  :  1013043

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来源: UNT Digital Library

【 摘 要 】

The National Spherical Torus Experiment (NSTX, [M. Ono et al., Nucl. Fusion 40, 557 (2000)]) routinely operates with neutral beam injection as the primary system for heating and current drive. The resulting fast ion population is super-Alfv#19;enic, with velocities 1 < vfast=vAlfven < 5. This provides a strong drive for toroidicity-induced Alfv#19;en eigenmodes (TAEs). As the discharge evolves, the fast ion population builds up and TAEs exhibit increasing bursts in amplitude and down-chirps in frequency, which eventually lead to a so-called TAE avalanche. Avalanches cause large (≤ 30%) fast ion losses over ~ 1 ms, as inferred from the neutron rate. The increased fast ion losses correlate with a stronger activity in the TAE band. In addition, it is shown that a n = 1 mode with frequency well below the TAE gap appears in the Fourier spectrum of magnetic fluctuations as a result of non-linear mode coupling between TAEs during avalanche events. The non-linear coupling between modes, which leads to enhanced fast ion transport during avalanches, is investigated.