Rotation dynamics and stability of collisional edge layers in tokamak plasmas

An earlier neoclassical transport theory for a collisional edge layer with steep radial gradients in the toroidal damping timescale is extended, to include also the faster poloidal damping timescale. In order to determine the stability behaviour of poloidal and toroidal rotations in a tokamak plasma, a two-timescale analysis is applied. It is observed that the poloidal and toroidal spin-up tendencies are strongly coupled by nonlocal interactions, although these evolve essentially on different timescales. Effects of charge exchange interactions, neutral beam injection, and a radial polarization current on both rotation speeds are consistently included in the model.