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

关键词: AMPLITUDES;    BEAM INJECTION;    FLUCTUATIONS;    HEATING;    NEUTRONS;    TRANSPORT Oscillations;    Nonlinear;    Mode Coupling;    Tokamaks;    NSTX;    Spherical Torus;   

DOI  :  10.2172/1013043
RP-ID  :  PPPL-4614
PID  :  OSTI ID: 1013043
Others  :  TRN: US1102952

学科分类：原子、分子光学和等离子物理

美国|英语

来源: SciTech Connect

【 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 enic, with velocities 1 < vfast=vAlfven < 5. This provides a strong drive for toroidicity-induced Alfv 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.