Effects of wave damping and finite perpendicular scale on three-dimensional Alfven wave parametric decay in low-beta plasmas

TL;DR

This study uses 3D hybrid simulations to explore how wave damping and finite perpendicular scales influence the parametric decay instability of kinetic Alfvén waves in low-beta plasmas, revealing damping effects are critical while perpendicular scale is not.

Contribution

First 3D open-boundary hybrid simulations of kinetic Alfvén wave PDI in low-beta plasmas, clarifying the roles of damping and wave scale effects.

Findings

Wave damping strongly limits PDI excitation.

Perpendicular wave scale has negligible effect on instability growth.

Theoretical analysis supports simulation results.

Abstract

Shear Alfven wave parametric decay instability (PDI) provides a potential path toward significant wave dissipation and plasma heating. However, fundamental questions regarding how PDI is excited in a realistic three-dimensional (3D) open system and how critically the finite perpendicular wave scale--as found in both laboratory and space plasmas--affects the excitation remain poorly understood. Here, we present the first 3D, open-boundary, hybrid kinetic-fluid simulations of kinetic Alfven wave PDI in low-beta plasmas. Key findings are that the PDI excitation is strongly limited by the wave damping present, including electron-ion collisional damping (represented by a constant resistivity) and geometrical attenuation associated with the finite-scale Alfven wave, and ion Landau damping of the child acoustic wave. The perpendicular wave scale alone, however, plays no discernible role: waves of different perpendicular scales exhibit similar instability growth as long as the magnitude of the parallel ponderomotive force remains unchanged. These findings are corroborated by theoretical analysis and estimates. The new understanding of 3D kinetic Alfv\'en wave PDI physics is essential for laboratory study of the basic plasma process and may also help evaluate the relevance/role of PDI in low-beta space plasmas.