Benchmarking of the Gyrokinetic Microstability Codes GENE, GS2, and GYRO over a Range of Plasma Parameters*

Comparing results (linear frequencies, eigenfunctions, and nonlinear fluxes) from different gyrokinetic codes as a means of verification (benchmarking) is only convincing if the codes agree over a wide range of plasma conditions. Otherwise, agreement may simply be fortuitous. We present here linear and nonlinear comparisons of the Eulerian codes GENE, GS2, and GYRO for a variety of JET discharges. The discharges include a simplified, 2-species, circular geometry case based on an actual JET discharge, an L-mode discharge with a significant fast ion pressure fraction, and a carbon-wall low triangularity hybrid discharge. All discharges were studied at rho=0.33 where significant ion temperature peaking is observed. The benchmarking is carried out to verify the GENE predictions that fast-ion-enhanced electromagnetic stabilization is the main contributor to the low ion heat flux.