TOROIDAL GYRO-LANDAU FLUID MODEL TURBULENCE SIMULATIONS IN A NONLINEAR BALLOONING MODE REPRESENTATION WITH RADIAL MODES

The method of Hammett and Perkins [Phys. Rev. Lett. 64, 3019 (1990)] to model Landau damping has been recently applied to the moments of the gyrokinetic equation with curvature drift by Waltz, Dominguez, and Hammett [Phys. Fluids B 4, 3138 (1992)]. The higher moments are truncated in terms of the lower moments (density, parallel velocity, and parallel and perpendicular pressure) by modeling the deviation from a perturbed Maxwellian to fit the kinetic response function at all values of the kinetic parameters: k\\v(th)/omega, b = (k perpendicular-to rho)2/2, and omega(D)/omega. Here the resulting gyro-Landau fluid equations are applied to the simulation of ion temperature gradient (ITG) mode turbulence in toroidal geometry using a novel three-dimensional (3-D) nonlinear ballooning mode representation. The representation is a Fourier transform of a field line following basis (k(y)',k(x)',z') with periodicity in toroidal and poloidal angles. Particular emphasis is given to the role of nonlinearly generated n = 0 (k(y)' = 0, k(x)' not-equal 0) ''radial modes'' in stabilizing the transport from the finite-n ITG ballooning modes. Detailing the parametric dependence of toroidal ITG turbulence is a key result.