Abstract
The internal structure of the toroidicity-induced Alfvén eigenmode (TAE) is studied by comparing soft x-ray profile and beam ion loss data taken during TAE activity in the DIII-D tokamak [W. W. Heidbrink et al., Nucl. Fusion 37, 1411 (1997)] with predictions from theories based on ideal magnetohydrodynamic (MHD), gyrofluid, and gyrokinetic models. The soft x-ray measurements indicate a centrally peaked eigenfunction, a feature which is closest to the gyrokinetic model’s prediction. The beam ion losses are simulated using a guiding center code. In the simulations, the TAE eigenfunction calculated using the ideal MHD model acts as a perturbation to the equilibrium field. The predicted beam ion losses are an order of magnitude less than the observed ∼6%–8% losses at the peak experimental amplitude of δBr/B0≃2–5×10−4.
Highlights
Toroidicity-induced Alfven eigenmodesTAEsare fastion driven instabilities that can cause energetic particle losses in tokamaks. These losses are a concern for future devices with reactor-like plasmas since losses significantly degrade performance and escaping particles may cause damage to the vacuum vessel and to plasma-facing components
The first set of data consists of soft x-ray measurements from two arraysone array has a vertical view of the plasma while the other has a horizontal viewon DIII-D during TAE activity
Three separate wave codes that feature different physical models are used to calculate the linear response of the plasma. ͑Only one of the codes is used for the particle simulation analysis, see Sec
Summary
Toroidicity-induced Alfven eigenmodesTAEsare fastion driven instabilities that can cause energetic particle losses in tokamaks. The amplitude of the fluctuations did not agree with predictions from ideal and resistive MHD models, it compared fairly well with the predictions of a model retaining Landau damping and finite Larmor radiusFLReffects For this model, the comparison yielded reduced 2’s of 1.2 and 1.6, respectively, for two different toroidal mode numbers. The first set of data consists of soft x-ray measurements from two arraysone array has a vertical view of the plasma while the other has a horizontal viewon DIII-D during TAE activity These data depend directly on the mode’s spatial structure. Drops in this signal imply significant losses of beam ions To properly make this comparison, we use a guiding center code to simulate fast ion motion in the presence of TAE activity, similar to the work done for fishbones on PDX..
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