Particle Scattering off of Right-Handed Dispersive Waves

TL;DR

This paper investigates how energetic electrons scatter off dispersive, right-handed plasma waves, extending existing models to account for multiple waves and validating results with Particle-in-Cell simulations.

Contribution

It introduces a modified analytic model for particle scattering in the plasma frame involving multiple dispersive waves, validated against PIC simulations.

Findings

No microscopic diffusion observed for single wave interactions.

Distribution broadening occurs despite lack of microscopic diffusion.

High amplitude and multiple waves cause deviations from the model.

Abstract

Resonant scattering of fast particles off low frequency plasma waves is a major process determining transport characteristics of energetic particles in the heliosphere and contributing to their acceleration. Usually, only Alfv\'en waves are considered for this process, although dispersive waves are also present throughout the heliosphere. We investigate resonant interaction of energetic electrons with dispersive, right-handed waves. For the interaction of particles and a single wave a variable transformation into the rest frame of the wave can be performed. Here, wellestablished analytic models derived in the framework of magnetostatic quasi-linear theory (QLT) can be used as a reference to validate simulation results. However, this approach fails as soon as several dispersive waves are involved. Based on analytic solutions modeling the scattering amplitude in the magnetostatic limit, we present an approach to modify these equations for the use in the plasma frame. Thereby we aim at a description of particle scattering in the presence of several waves. A Particle-in-Cell (PiC) code is employed to study wave-particle scattering on a micro-physically correct level and to test the modified model equations. We investigate the interactions of electrons at different energies (from 1 keV to 1 MeV) and right-handed waves with various amplitudes. Differences between model and simulation arise in the case of high amplitudes or several waves. Analyzing the trajectories of single particles we find no microscopic diffusion in the case of a single plasma wave, although a broadening of the particle distribution can be observed.