THEORY OF A HIGH-N TOROIDICITY-INDUCED SHEAR ALFVEN EIGENMODE IN TOKAMAKS

A high-n WKB-ballooning mode equation is employed to study toroidicity-induced shear Alfvén eigenmodes (TAE) in s-α space, where s = (r/q) (dq/dr) is the magnetic shear and α = - (2Rq 2/B2) (dp/dr) is the normalized pressure gradient for tokamak plasmas. In the ballooning mode first stability region, TAE modes are found to exist only for α less than some critical value αc. It is found that these TAE modes reappear in the ballooning mode second stability region for bands of α values. The global envelope structures of these TAE modes are studied by the Wentzel-Kramers-Brillouin (WKB) method and are found to be bounded radially if the local mode frequency has a maximum in radius. © 1990 American Institute of Physics.