Gyrokinetic turbulence simulations at high plasma beta

Electromagnetic gyrokinetic turbulence simulations employing Cyclone Base Case parameters are presented for $\beta$ values up to and beyond the kinetic ballooning threshold. The $\beta$ scaling of the turbulent transport is found to be linked to a complex interplay of linear and nonlinear effects. Linear investigation of the kinetic ballooning mode is performed in detail, while nonlinearly, it is found to dominate the turbulence only in a fairly narrow range of $\beta$ values just below the respective ideal limit. The magnetic transport scales like ${\beta }^2$ and is well described by a Rechester–Rosenbluth-type ansatz.