# Fully kinetic simulation study of ion-acoustic solitons in the presence of trapped electrons

## TL;DR

This study uses fully kinetic simulations to verify the stability and collision behavior of ion-acoustic solitons with trapped electrons, providing insights beyond fluid theory predictions.

## Contribution

It demonstrates the stability of ion-acoustic solitons with trapped electrons during collisions using a fully kinetic Vlasov simulation approach, extending fluid theory insights.

## Key findings

- Solitons retain their features after collisions.
- Collision behavior is more complex than fluid theory predicts.
- Solitons exchange trapped populations during interactions.

## Abstract

The nonlinear fluid theory developed by Schamel suggests a modified KdV equation to describe the temporal evolution of ion acoustic (IA) solitons in the presence of trapped electrons. The validity of this theory is studied here by verifying solitons main characteristic, i.e., stability against successive mutual collisions. We have employed a kinetic model as a more comprehensive theory than the fluid one, and utilized a fully kinetic simulation approach (both ions and electrons are treated based on the Vlasov equation). In the simulation approach, these solitons are excited self-consistently by employing the nonlinear process of IA solitons formation from an initial density perturbation (IDP). The effect of the size of IDPs on the chain formation is proved by the simulation code as a benchmark test. It is shown that the IA solitons, in presence of trapped electrons, can retain their features (both in spatial and velocity direction) after successive mutual collisions. The collisions here include encounters of IA solitons with the same trapping parameter, while differing in size. Kinetic simulation results reveal a complicated behavior during a collision between IA solitons in contrast to the fluid theory predictions and simulations. In the range of parameters considered here two oppositely propagating solitons rotate around their collective center in the phase space during a collision, independent of their trapping parameters. Furthermore, they exchange some portions of their trapped populations.