Multiple helicity quasilinear ballooning modes

The validity of the ballooning mode transformation in quasilinear calculations is examined. If the range of interacting helicities is too large, the equivalence of harmonics is destroyed. The criterion for the validity of the ballooning mode transformation is Lm δn δm much-lt n, where δm and δn are the spreads of excited poloidal and toroidal harmonics, respectively, and Lm is the number of harmonics necessary to represent the quasilinear pressure profile flattening. The quasilinear formalism of Riedel [Phys. Fluids B 1, 1780 (1989)] is generalized to the multiple toroidal helicity case