Existence of core localized toroidicity-induced Alfvén eigenmode

The core-localized toroidicity-induced Alfvén eigenmode (TAE) is shown to exist at finite plasma pressure due to finite aspect ratio effects in tokamak plasma. The new critical beta for the existence of the TAE mode is given by α≊3ε+2s2, where ε=r/R is the inverse aspect ratio, s is the magnetic shear and α=−Rq2dβ/dr is the normalized pressure gradient. In contrast, previous critical α is given by α≊s2. In the limit of s≪√r/R, the new critical α is greatly enhanced by the finite aspect ratio effects.