Modeling a turbulent collisionless space plasma as a Langevin type system

Abstract:

There is wide evidence that in many space environments as the solar wind, the Velocity
Distribution Function (VDF) of electrons presents interesting non-thermal behaviors as heavy
tails (power-law behavior at large energies that can be fitted by the well-known kappa functions)
and skewness in the direction of background magnetic field. By separate, the origin of both
properties (power-law tails and skewness), and the consequences that they produce on space
plasmas have been addressed in several observational and theoretical studies. However, a
complete understanding on the origin of distributions exhibiting power-law tails is and skewness
has already to be done. In this work we present the results about our study, which aims to answer
the following: how can we model the microscopic dynamics of magnetized, turbulent and
collisionless space plasmas so that the distribution has power-law tails and skewness at the same
time? For this, here we show an alternative Langevin type force equation to model the first
principles dynamics of electrons in a space plasma, exploring how the micro scales relates to
meso and macro scales. We focus on quantifying the heavy tails (measured by the kappa power
index) and skewness throughout the moments of the VDF. Our numerical results show a clear
scaling relation between the Reynolds number and both, the kappa index and the skewness of the
steady-state particle distribution, suggesting that turbulence plays a key role on the formation and
relaxation of space plasma non-thermal particle populations.