Ion diffusion and acceleration in plasma turbulence

Abstract

Particle transport, acceleration and energisation are phenomena of major importance for both space and laboratory plasmas. Despite years of study, an accurate theoretical description of these effects is still lacking. Validating models with self-consistent, kinetic simulations represents today a new challenge for the description of weakly-collisional, turbulent plasmas. We perform two-dimensional (2D) hybrid-PIC simulations of steadystate turbulence to study the processes of diffusion and acceleration. The chosen plasma parameters allow to span different systems, going from the solar corona to the solar wind, from the Earth's magnetosheath to confinement devices. To describe the ion diffusion, we adapted the Nonlinear Guiding Center (NLGC) theory to the 2D case. Finally, we investigated the local influence of coherent structures on particle energisation and acceleration: current sheets play an important role if the ions Larmor radii are on the order of the current sheets size. This resonance-like process leads to the violation of the magnetic moment conservation, eventually enhancing the velocity-space diffusion.PACS codes: Authors should not enter PACS codes directly on the manuscript, as these must be chosen during the online submission process and will then be added during the typesetting process (see http://www.aip.org/pacs/ for the full list of PACS codes)

Statistical Analysis of Ions in Two-Dimensional Plasma Turbulence

“…The details are summarised in Table 1. More details on these simulations are reported in previous works [Servidio et al, 2016, Pecora et al, 2018.…”

Particle acceleration in strong MHD turbulence

“…In this regard, higher order effects, such as those discussed above, are a necessity, see Ref. [18] for a related discussion.…”

“…Recent numerical simulations suggest that particles can draw energy from their interaction with the coherent structures of a turbulent bath [18,19], and it is known that particles exploring a sheared velocity field with a finite mean free path can gain energy in a non-resonant fashion [20][21][22][23]. However, a definite model able to relate the physics of particle acceleration with the characteristics of the structures of a turbulent bath remains lacking.…”

Parker Solar Probe Observations of Helical Structures as Boundaries for Energetic Particles

“…These scenarios lack what would be called intermittency in turbulence theory. Indeed, a variety of indications, both theoretical (Ambrosiano et al 1988;Drake et al 2006;Dalena et al 2012;Pecora et al 2018) and observational (Mazur et al 2000;Tessein et al 2013Tessein et al , 2016Khabarova & Zank 2017), build a case that interactions of particles with turbulence is structured and inhomogeneous. Depending on the topology and connectivity of the magnetic field, these interactions may involve temporary trapping (Ruffolo et al 2003), as well as exclusion from certain regions of space (Kittinaradorn et al 2009).…”