Drift-wave eigenmodes in toroidal plasmas

The eigenmode equation describing ballooning drift waves in toroidal plasmas is investigated both analytically and numerically. Two branches of eigenmodes are identified. One is slab-like and the other is a new branch induced by finite toroidal coupling. The slab-like eigenmodes correspond to unbounded states and experience finite shear damping. The toroidicity-induced eigenmodes, however, can become local quasi-bounded states with negligible shear damping. Both branches of eigenmodes may exist simultaneously. The corresponding analytical theories are also presented.