Particle pinch in gyrokinetic simulations of closed field-line systems.

Gyrokinetic simulations of small-scale turbulent transport in a closed magnetic field-line plasma geometry are presented. The simulations are potentially applicable to dipolar systems such as the levitated dipole experiment (LDX) [J. Kesner, Plasma Phys. Rep. 23, 742 (1997).] and planetary magnetospheres, as well as simpler systems such as the Z pinch. We report here for the first time the existence of a robust particle (and weaker temperature) pinch regime, in which the particles are transported up the density gradient. The particle pinch is driven by non-MHD entropy-mode turbulence at k(⊥) ρ(i) ∼ 1 and particle pinch appears at larger η ≡ L(n)/L(T) ≳ 0.7, consistent with quasilinear theory. Our results suggest that entropy-mode transport will drive the LDX plasma profiles toward a state with η ∼ 0.7 and pressure gradients that are near marginal ideal MHD interchange-mode stability.