Arbitrary plasma shape and trapped electron modes in the GEM gyrokinetic electromagnetic turbulence simulation code

Here the recent developments in GEM, a quite comprehensive Gyrokinetic Electromagnetic (GEM) turbulence code are described. GEM is a δf particle turbulence simulation code that has kinetic electrons and electromagnetic perturbations. The key elements of the GEM algorithm are: (1) the parallel canonical formulation of the gyrokinetic system of equations [1]; (2) an adjustable split-weight scheme for kinetic electrons [2]; and (3) a high-β algorithm for the Ampere’s equation [3]. Additionally, GEM use a two-dimensional (2D) domain decomposition and runs efficiently on a variety of high performance architectures. GEM is now extended to include arbitrary toroidal equilibrium profiles and flux-surface shapes [4]. The domain is an arbitrarily sized toroidal slice with periodicity assumed in the toroidal direction. It is global radially and poloidally along the magnetic field. Results are presented that demonstrate the effect of plasma shaping on the Ion-Temperature-Gradient (ITG) driven instabilities. An example of nonlinear simulation of the finite-β modified ITG turbulence in general geometry is also given. Finally, collisionless Trapped Electron Modes (TEM) are investigated and shown here is the transition from the TEM dominated core region to the Drift-Wave dominated edge region as the density gradient increases.