Non-linear theory of collisional drift modes, anomalous skin effect and enhanced penetration of particles during fuelling

The non-linear evolution of drift waves is described in the framework of weak-turbulence theory and of Taylor's strong-toroidal-coupling approximation. It is found that when the stabilizing effect of shear is annihilated by the toroidal coupling due to magnetic curvature, the radial wavelength of the modes increases with increasing amplitude until ion Landau damping balances the de-stabilizing effect of the electrons, which, in its turn, decreases with increasing turbulence level. The anomalous particles and electron thermal transports are estimated for the collisional drift instability driven by inverse electron temperature gradients. It is shown that the corresponding fluxes are towards the regions of lower density and electron temperature, respectively. Furthermore, they may exceed the neoclassical fluxes by three orders of magnitude (or even more) as required to explain the anomalous skin effect observed in tokamaks and the rapid penetration of cold particles to the plasma core during fuelling by injection of cold neutrals.