# Extreme driven ion acoustic waves

## TL;DR

This paper investigates how chirped frequency drives can excite large, nonlinear ion acoustic waves in plasma, leading to extreme localized density peaks through a process called autoresonance, confirmed by simulations and theoretical analysis.

## Contribution

It introduces a fully nonlinear fluid model and applies Whitham's variational principle to analyze autoresonant ion acoustic waves, revealing conditions for extreme wave formation.

## Key findings

- Formation of sharply peaked ion acoustic waves with high local density
- Wave amplitude bounded by kinetic wave-breaking limit
- Confirmation of fluid model predictions via Vlasov-Poisson simulations

## Abstract

Excitation of large amplitude strongly nonlinear ion acoustic waves from a trivial equilibrium by a chirped frequency drive is discussed. Under certain conditions, after passage through the linear resonance in this system, the nonlinearity and the variation of parameters work in tandem to preserve the phase-locking with the driving wave via excursion of the excited ion acoustic wave in its parameter space, yielding controlled growth of the wave amplitude. We study these autoresonant waves via a fully nonlinear warm fluid model and predict formation of sharply peaked (extreme) ion acoustic excitations with local ion density significantly exceeding the unperturbed plasma density. The driven wave amplitude is bounded by the kinetic wave-breaking, as the local maximum fluid velocity of the wave approaches the phase velocity of the drive. The Vlasov-Poisson simulations are used to confirm the results of the fluid model and the Whitham's averaged variational principle is applied in analyzing evolution of the autoresonant ion acoustic waves.