Existence of finite and anisotropic heavy ion parallel compressibility pinch in the gyrokinetic turbulence

Abstract

Turbulence-driven heavy ion transport in hot magnetized plasma is investigated by means of the gyrokinetic theory and simulations. A finite heavy ion parallel compressibility pinch (Γ_{s,∥}) is found in the gyrokinetic framework, in contrast to the conventional understanding that Γ_{s,∥} is negligible. A perturbation theory clarifies the turbulence frequency dependence of Γ_{s,∥}, resolving the discrepancy with experimental observations. It is also predicted by a nonlocal approach of the parallel advection term that Γ_{s,∥} is strongly anisotropic on a magnetic surface. The parameter dependence shows that decreasing the heavy ion mass m_{s} strongly enhances Γ_{s,∥} through kinetic effects, leading to a deviation from the 1/m_{s} scaling. Moreover, the pinch direction can be reversed in nonlinear trapped electron mode turbulence through the inverse cascade.