Observation of beta-induced Alfvén eigenmodes in the DIII-D tokamak.

Author(s): Heidbrink, WW; Strait, EJ; Chu, MS; Turnbull, AD | Abstract: Energetic ions can drive Alfven gap modes unstable, causing large losses of fast ions. Toroidicity-induced Alfven eigenmodes (TAE) were expected to disappear into the shear Alfven continuum and become stable as the plasma beta increased. Although TAE modes may disappear, another dangerous instability with similar properties but approximately half the TAE frequency appears in a spectral gap that is created by finite beta effects. The measured frequency of the new mode agrees with the theoretical frequency of beta-induced Alfven eigenmodes. © 1993 The American Physical Society.