Natural fluctuations in un-magnetized and magnetized plasmas

Abstract

There are still open issues within the fluctuation theory of plasmas, in view of the difficulty of formulating adequate theoretical approaches and solving the related equations in particular regimes. A promising alternative approach is direct microphysical modeling based on first principles, as successfully applied to neutral rarefied fluids. Within this approach, the equations of motion of a large ensemble of charged particles are solved numerically while correlations are obtained from statistical analysis of the ensemble at different times. As a first step, in this work we validate the data analysis technique adopted in this numerical scheme for the case of an electron ensemble neglecting Coulomb interactions. The simulation results are compared with the analytical theory of 'natural' fluctuations for both unmagnetized and magnetized plasmas. For the latter, the derivations for arbitrary average distribution functions are presented.

Molecular dynamics calculation of the spectral densities of plasma fluctuations

“…The numerical method employed in this work for the calculation of the space–time correlation function of electron density fluctuations is based on molecular dynamics in the space using an importance sampling Monte Carlo (Tolias et al. 2015). In contrast to Tolias et al.…”

“…In contrast to Tolias et al. (2015) that focused on the non-interacting electron gas and the spectral densities of natural electron density fluctuations, here interactions are included. In the non-relativistic limit , magnetic field generation and retardation effects are negligible.…”

“…1984; Tolias et al. 2015), there are no analytic expressions for . However, convenient closed form relations exist for its space–time Fourier transform , typically coined as the spectral density of the plasma density fluctuations.…”

The finite probe size effect in fluctuation measurements; application to dusty plasmas

“…By employing the definition of natural fluctuations, a closed form relation can be found for the ensemble average of the product of two natural fluctuating components of the microscopic phase-space density at different time instants and different positions (Ichimaru & Yakimenko 1973; Yakimenko & Zagorodny 1974; Tolias et al. 2015). In the absence of external electromagnetic fields, its space–time Fourier transform, also known as the natural correlator, is given by Tsytovich (1989, 1995), Tolias et al.…”

A technique for plasma velocity-space cross-correlation

“…In our case, we use a phase space correlation measurement. Correlations of plasma quantities have an extensive history, with recent examples using density 11 , magnetic fields 12 , and fieldparticle correlations 13,14 to investigate fluctuations, magnetic power spectra, and collisionless energy transfer in turbulence respectively. This illustrates a useful property of correlation functions: depending on the plasma quantities correlated, they provide insight into specific aspects of plasma behavior.…”