Open AccessNon-linear Dynamics Of Toroidicity-induced Alfven Eigenmodes On The National Spherical Torus Experiment
Author(s) -
M Podesta,
N A Crocker,
E. D. Fredrickson,
N N Gorelenkov,
W W Heidbrink,
S Kubota,
B P LeBlanc
Publication year - 2011
Language(s) - English
Resource type - Reports
DOI - 10.2172/1013043
Subject(s) - physics , amplitude , ion , atomic physics , population , coupling (piping) , torus , fusion , plasma , computational physics , nuclear physics , optics , materials science , geometry , mathematics , demography , quantum mechanics , sociology , metallurgy , linguistics , philosophy
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