Edge turbulence from the tokamak core

It is well known that the tokamak edge plasma is strongly turbulent, but the source of the turbulence is unknown. In this work, the authors consider the possibility that edge turbulence originates as core fluctuations which propagate radially outward. This scenario has not been previously considered seriously, assumedly because core fluctuations are small amplitude, left-angle n/n0 right-angle rms much-lt O(1), with too low a level to drive the large amplitude, edge fluctuations, which have left-angle n/n0 right-angle rms ∼ O(1). Upon closer inspection, this argument may be mistaken, since experimental observations suggest that the increase of left-angle n/n0 right-angle rms may come more from the decrease of n0 at the plasma edge, while left-angle n right-angle rms stays roughly constant. Of course, wave energy is related more to n than to n/n0, so this observation suggests that no local energy source may be required to explain edge fluctuation levels. Similar arguments apply to field fluctuations, eφ/Te. The open-quotes trueclose quotes situation in a tokamak is complicated, with a turbulent spectrum coupled both nonlinearly and toroidally, propagating in an inhomogeneous medium. Here, the authors consider a simplified model of a slab plasma with a radial density gradient in a straight uniform magnetic field. The magnetic field is taken as unsheared, with the assumption that the localizing influence of magnetic shear is roughly offset by toroidal coupling. A drift wave of single poloidal mode number is launched in the high density open-quotes core,close quotes propagating radially outward. This simple model gives insight into the behavior of a drift wave approaching the low density open-quotes edgeclose quotes region, including amplitude and wavelength variations, and whether the wave breaks or reflects