Drift wave propagation as a source of plasma edge turbulence: Slab theory

In a recent work [N. Mattor and P. H. Diamond, Phys. Rev. Lett. 62, 486 (1994)], it was suggested that large amplitude turbulence in edge plasmas [ñ/n0∼O(1)] could originate from the core, reaching large amplitude when encountering regions of low density and temperature. Here the slab model of that theory is elaborated on and generalized to the case of nonadiabatic electron dynamics. It is shown that a drift wave launched with ñ/n0≪1 in a dense region can propagate into a sparse region and amplify. It is shown that such waves cannot propagate into regions with a large increase of velocity, suggesting a simple explanation of the observed correlation between edge shear flows and high confinement (‘‘H’’ modes). It is shown that a wave launched in the adiabatic regime can become nonadiabatic when propagating into a low density and temperature edge region, suggesting a possible explanation for probe measurements.