Local Kinetic Effects in Two-Dimensional Plasma Turbulence

Using direct numerical simulations of a hybrid Vlasov-Maxwell model, kinetic processes are investigated in a two-dimensional turbulent plasma. In the turbulent regime, kinetic effects manifest through a deformation of the ion distribution function. These patterns of non-Maxwellian features are concentrated in space nearby regions of strong magnetic activity: the distribution function is modulated by the magnetic topology, and can elongate along or across the local magnetic field. These results open a new path on the study of kinetic processes such as heating, particle acceleration, and temperature anisotropy, commonly observed in astrophysical and laboratory plasmas.

Figure 1

(a) Shaded contours (zoom) of $j_z$ together with $a_z$ (isolines) and its $X$ points (black crosses). (b) Power spectra of ion density (green dotted), ion bulk velocity (red dashed), magnetic field (black solid), and electric field (dot-dashed blue). The Kolmogorov expectation $k^{-5/3}$ (gray dashed) is reported as a reference, while the vertical dashed line represents the ion skin depth wave number.

Figure 2

(a) PDF of the temperature anisotropy ${\lambda }_1/{\lambda }_3$ for all runs (arrows represent averages); (b) shaded-contour (zoom) of the anisotropy together with the inplane magnetic field lines (black); (c) PDF of the kurtosis ${\chi }_3$; (d) joint distribution of current gradients and anisotropy $g(|{\nabla }^2{\mathit{b}}_{\perp }|,{\lambda }_1/{\lambda }_3)$. In (a) and (c) the statistical error bars are also reported.

Figure 3

(a) Isosurfaces of the velocity distribution function $f({\mathit{x}}^{\star },\mathit{v})$, at a given spatial position ${\mathit{x}}^{*}\simeq (60,119)d_i$. (b) Two-dimensional cut of $f$ in the minimum variance frame. Thin (red) and thicker (blue) axis indicate ${\widehat{e}}_1$ and ${\widehat{e}}_3$, respectively. The magnetic field direction $\widehat{\mathit{B}}$ is represented with a thick (magenta) tube.

Figure 4

PDF of the cosine angle given by Eq. (4) for all runs. The horizontal (green) dot-dashed line represents the distribution in the case of random variables.