Electron acceleration from the interaction of three crossed parallel Alfv\'en waves

TL;DR

This study uses 2.5D PIC simulations to explore how three crossed Alfvén waves interact in plasma, revealing mechanisms for electron acceleration relevant to space physics phenomena like radiation belts and coronal loops.

Contribution

It demonstrates that a third Alfvén wave enhances electron acceleration through phase mixing and density gradients, extending previous two-wave interaction models.

Findings

Strong parallel electron beams are generated at density gradients.

A third wave amplifies electric fields and electron acceleration.

Interface waves facilitate phase mixing and energy transfer.

Abstract

We study the non-linear interaction of three parallel Alfv\'en wave packets (AWP) in an initially uniform plasma using 2.5D particle-in-a-cell (PIC) numerical simulations. We aim to help to explain the observation of suprathermal electrons by multiple Alfv\'en waves collision in regions where these waves are trapped like IAR (Ionospheric Alfv\'en Resonator), Earth radiation belts or coronal magnetic loops. In the context of APAWI process that have been described by Mottez (2012, 2015), the interaction of two parallel Alfv\'en waves (AW) generates longitudinal density modulations and parallel electric field at the APAWI crossing region that can accelerate particles effectively in the direction of the background magnetic field. Our simulations show that when a third parallel AWP of different initial position arrives at the APAWI crossing region, it gives rise to a strong parallel electron beams ($V \sim 5--7VTe$) at longitudinal cavity density gradients. We suggest that velocity drift from outgoing AW generates interface waves in the transverse direction, which allows propagating waves to develop parallel electric fields by phase mixing process when the transverse scale of the wavy density gradient (oblique gradient) is in the range of the electron inertial length.