Drift wave propagation as a source of plasma edge turbulence

It is suggested that large amplitude turbulence in edge plasmas could originate from core fluctuations propagating to the edge. It is shown that a drift wave launched with ñ/${\mathit{n}}_0$≪1 in a dense region can propagate into a sparse region and amplify, in both a slab and a torus. Propagation is cut off by a large velocity increase, suggesting a simple explanation of the observed correlation between edge shear flows and improved confinement (H modes). Evidence for such radial propagation might be found in asymmetries of fluctuations about the toroidal midplane.