Limits of applicability of the quasilinear approximation to the electrostatic wave-plasma interaction

TL;DR

This paper investigates the limitations of Quasilinear Theory in describing particle diffusion in plasma interactions with electrostatic waves, identifying thresholds where the theory fails through analytical and numerical methods.

Contribution

It provides analytical and numerical estimates of wave amplitude thresholds beyond which Quasilinear Theory becomes invalid in plasma wave-particle interactions.

Findings

QLT breaks down at high wave amplitudes

Velocity distribution evolution differs from QLT predictions at large amplitudes

Thresholds for QLT validity are quantitatively estimated

Abstract

The limitation of the Quasilinear Theory (QLT) to describe the diffusion of electrons and ions in velocity space when interacting with a spectrum of large amplitude electrostatic Langmuir, Upper and Lower hybrid waves, is analyzed. We analytically and numerically estimate the threshold for the amplitude of the waves above which the QLT breaks down, using a test particle code. The evolution of the velocity distribution, the velocity-space diffusion coefficients, the driven current, and the heating of the particles are investigated, for the interaction with small and large amplitude electrostatic waves, i.e. in both regimes, there where QLT is valid and there where it clearly breaks down.