Nonlinear quasi-steady state benchmark of global gyrokinetic codes

Two global gyrokinetic codes are benchmarked against each other by comparing simulation results in the case of ion temperature gradient driven (ITG) turbulence, in the adiabatic electron response limit. The two codes are the Eulerian code GENE and the Lagrangian Particle-In-Cell code ORB5 which solve the gyrokinetic equations. Linear results are presented, including growth rates, real frequencies and mode structure comparisons. Nonlinear simulations without sources are carried out with particular attention to considering the same initial conditions, showing identical linear phase and first nonlinear burst. Very good agreement is also achieved between simulations obtained using a Krook-type heat source, which enables to reach a quasi-steady state and thus to compare the heat diffusivity traces over a statistically meaningful time interval. For these nonlinear results, the radial zonal flow structure and shearing rate profile are also discussed. The very detailed comparisons presented may serve as reference for benchmarking other gyrokinetic simulation codes, in particular those which consider global geometry.