Induced Scattering of Strong Waves in Pair Plasmas

TL;DR

This paper investigates how strong electromagnetic waves interact with pair plasmas, revealing that nonlinearity depends on a specific parameter and that wave scattering is suppressed at high energies, with implications for fast radio bursts.

Contribution

The study revisits steady-state solutions for polarized waves in pair plasmas and demonstrates the applicability of linear scattering analysis even for strong waves when considering plasma motion.

Findings

Nonlinearity characterized by $a_0\omega_{pe}/\omega_0$ rather than $a_0$.

Linear analysis remains valid for $a_0 > 1$ with plasma Lorentz boost.

Wave scattering is suppressed when $a_0\omega_0/\omega_{pe} \\gg 1$.

Abstract

We study induced (stimulated) scattering of linearly polarized, strong electromagnetic waves in pair plasmas, which is crucial for understanding the propagation of fast radio bursts (FRBs). Magnetars are the most promising progenitors of FRBs, and FRBs propagate through the magnetar wind and successfully escape before being significantly scattered. We revisit the steady-state solution of linearly polarized electromagnetic waves in pair plasmas with arbitrary amplitude, and demonstrate that the nonlinearity is characterized by the nonlinearity parameter $a_0\omega_{pe}/\omega_0$ rather than the dimensionless amplitude $a_0$, where $\omega_{pe}$ is the electron plasma frequency and $\omega_0$ is the wave frequency. We follow the time evolution of the steady-state solution for the linear regime $a_0\omega_{pe}/\omega_0 \ll 1$ by performing one-dimensional particle-in-cell simulations, and show that the conventional linear analysis of induced scattering assuming $a_0 \ll 1$ is applicable even for $a_0 > 1$ when the Lorentz boost due to the plasma motion in the incident wave is considered. The saturation level is controlled by $a_0\omega_0/\omega_{pe}$, which corresponds to the ratio of the wave energy to the plasma energy, and the incident wave is hardly scattered for $a_0\omega_0/\omega_{pe} \gg 1$. We discuss the application of our results to FRBs.