Nonlinear kinetic transport in high-temperature plasmas due to turbulence and vortices in phase-space

Nonlinear transport in high-temperature plasmas due to turbulence and phase-space vortices is investigated through numerical simulations and theory. In this work, we investigate the diffusion of charged particles due to the presence of a prescribed turbulent electric field (Langmuir and ion-acoustic waves with random phases), the diffusion due to phase-space vortices in a turbulent background, and the dynamics of solitary phase-space vortex. In this work, two codes were used, one for test particle trajectories named PERKS used for the diffusion studies, and a second kinetic, Vlasov-Poison solver named COBBLES used to perform the analysis of phase-space vortices. Turbulent diffusion at a low Kubo number, defined as the ratio between the autocorrelation time and characteristic trapped bounce time of the electric field K= tau_0/tau_b, is correctly predicted by quasi-linear theory, including resonance broadening. However, for large Kubo numbers, a new regime is reached where the diffusion coefficient increases and scales as a power law E^{3/2}, which is explained by a random-walk diffusion of the centers of trapped-particle trajectories. In the presence of phase-space vortices, diffusion is divided into two regimes: The first one is where diffusion is dominant, particles experience random-walk trajectories, and diffusion is predicted as if no structure is present in the plasma. In the second case, where structures are dominant over turbulence, particle dynamics is that of trapped-particle trajectories, and diffusion is predicted by the one generated due to the structure. Finally, the dynamic of solitary Schamel phase-space vortices is investigated. Limits and discrepancies of the analytical theory with respect to numerical simulations are discussed, particularly the large impact the ion-distribution function and small variations of distribution gradients have over the dynamics of electron vortices.