3-DIMENSIONAL COMPUTATION OF DRIFT ALFVEN TURBULENCE

A transcollisional, electromagnetic fluid model, incorporating the par allel heat Bur as a dependent variable, is constructed to treat electr on drift turbulence in the regime of tokamak edge plasmas at the L-H t ransition. The resulting turbulence is very sensitive to the plasma be ta throughout this regime, with the scaling with rising beta produced by the effect of magnetic induction to slow the Alfvenic parallel elec tron dynamics and thereby leave the turbulence in a more robust, non-a diabatic state, Magnetic flutter and curvature have a minor qualitativ e effect on the turbulence mode structure and on the beta scaling, eve n when their quantitative effect is strong. Transport by magnetic flut ter is small compared to that by the E x B flow eddies. Fluctuation st atistics show that while the turbulence shows no coherent structure, i t is coupled strongly enough so that neither density nor temperature f luctuations behave as passive scalars. Both profile gradients drive th e turbulence, with the total thermal energy transport varying only wea kly with the gradient ratio, d log T/d log n. Scaling with magnetic sh ear is pronounced, with stronger shear leading to lower drive levels. Scaling with either collision frequency or magnetic curvature is weak, consistent with their weak qualitative effect. The result is that ele ctron drift turbulence at L-H transition edge parameters is drift Alfv en turbulence, with both ballooning and resistivity in a clear seconda ry role. The contents of the drift Alfven model will form a significan t part of any useful first-principles computation of tokamak edge turb ulence.