3-DIMENSIONAL FLUID SIMULATIONS OF THE NONLINEAR DRIFT-RESISTIVE BALLOONING MODES IN TOKAMAK EDGE PLASMAS

A three-dimensional study of the turbulence and sheared flow generated by the drift-resistive ballooning modes in tokamak edge plasmas has b een completed. The fluid simulations show that 10%-15% percent density fluctuations can develop in the nonlinear state when the self-consist ently generated shear flow is suppressed. These modes are also found t o give rise to poloidally asymmetric particle transport. Characteristi c scale lengths of these fluctuations are isotropic in the plane trans verse to B and smaller than the connection length along the field line . Sheared poloidal flow is self-consistently driven by both the Reynol ds stress and the Stringer mechanisms. In the presence of self-consist ent shear flow, the transverse spectrum is no longer isotropic transve rse to B. The vortices become elongated in the poloidal direction. Als o, there is a substantial reduction in both the level of fluctuations of the density and potential and the associated particle transport. Th ese features are in qualitative agreement with L-H transitions observe d in tokamaks.