Realistic magnetic equilibria in global nonlinear gyrokinetic simulations

Magnetic equilibrium effects such as finite-beta, triangularity and elongation have been shown in some cases to have a significant effect on drift-wave type microinstabilities. Here, we study these effects on ion-temperature-gradient driven turbulence using a fully nonlinear and global gyrokinetic simulation with realistic tokamak magnetic equilibria (in contrast to past studies using unshifted circles). Progress has been made integrating numerically calculated magnetic equilibria into a global nonlinear electrostatic gyrokinetic δf simulation. The gyrokinetic code evolves the equations of motion and solves for the electrostatic field in cylindrical (R, Z, φ) coordinates. The poloidal magnetic flux function ψ, its gradients, the toroidal magnetic field and the plasma pressure have been mapped onto the same (R, Z) coordinates yielding all the necessary equilibrium quantities. The gyrokinetic simulation runs on the Cray T3D massively parallel supercomputer using a domain decomposition in the toroidal direction with PVM. The code scales very well with a speed of approximately 14 Mflops per processor. We plan to investigate the differences between circular and shaped plasmas for low to intermediate values of n, studying the linear eigenmodes, as well as, the nonlinear saturated turbulent fluctuations and associated heat transport. Simulation results using an equilibrium from the TFTR ERS mode, where there is a strong shift in the magnetic axis may also be reported