Plasma acceleration by the interaction of parallel propagating Alfv\'en waves

TL;DR

This paper demonstrates that crossing Alfvén waves in a plasma generate non-oscillating electromagnetic fields capable of efficiently accelerating particles, with potential relevance to space plasma phenomena like Earth's auroral zones.

Contribution

It introduces a combined analytical and simulation study showing how crossing Alfvén waves produce particle acceleration and plasma cavities, advancing understanding of space plasma dynamics.

Findings

Non-oscillating electromagnetic fields are generated when Alfvén waves cross.

Particle acceleration leads to plasma cavities and ion beams.

Results are consistent with space plasma observations, such as Earth's auroral zone.

Abstract

It is shown that two circularly polarised Alfv\'en waves that propagate along the ambient magnetic field in an uniform plasma trigger non oscillating electromagnetic field components when they cross each other. The non-oscilliating field components can accelerate ions and electrons with great efficiency. This work is based on particle-in-cell (PIC) numerical simulations and on analytical non-linear computations. The analytical computations are done for two counter-propagating monochromatic waves. The simulations are done with monochromatic waves and with wave packets. The simulations show parallel electromagnetic fields consistent with the theory, and they show that the particle acceleration result in plasma cavities and, if the waves amplitudes are high enough, in ion beams. These acceleration processes could be relevant in space plasmas. For instance, they could be at work in the auroral zone and in the radiation belts of the Earth magnetosphere. In particular, they may explain the origin of the deep plasma cavities observed in the Earth auroral zone.