ExB shear flows and electromagnetic gyrofluid turbulence

Low frequency tokamak edge turbulence is modelled numerically using gyroflu id equations for electrons and ions on an equal footing. The electrons are electromagnetic, and arbitrarily strong finite gyroradius effects are inclu ded for the ions. Computations are in a globally consistent truncation of f lux surface geometry arising from ideal tokamak equilibria. The turbulence is similar to that in the fluid model in steep gradient regimes, for which the electron transit frequency is comparable to that of the turbulence. The nonlinear drift wave instability is shown to be caused by E x B self-advec tion, and is similar for both two-and three-dimensional models. The turbule nce always has drift wave mode character for the parameter regime of intere st, except when the ideal ballooning threshold is reached. Turbulence inter acts strongly with E x B shear flows, but does not build the flow shear to significant levels by itself. On the other hand, an imposed shear layer ari sing from the neoclassical equilibrium of the edge region does have the nec essary properties and scaling to eventually result in a credible edge trans port transition scenario. (C) 2000 American Institute of Physics. [S1070-66 4X(00)92205-5].