Global limits on kinetic Alfv\'{e}non speed in quasineutral plasmas

TL;DR

This paper derives the global speed limits for kinetic Alfvén solitons in quasineutral plasmas, revealing how plasma parameters and propagation angle influence soliton speeds relative to the Alfvén speed.

Contribution

It provides an exact solution for the matching conditions of kinetic Alfvén solitons in various quasineutral plasmas, highlighting the role of propagation angle and plasma parameters.

Findings

Kinetic solitons can be sub- or super-Alfvénic depending on plasma conditions.

Upper and lower soliton speed limits are independent of fractional plasma parameters.

Propagation angle significantly affects the soliton speed range.

Abstract

Large amplitude kinetic Alfv\'{e}non (exact Alfv\'{e}n soliton) matching condition is investigated in quasineutral electron-ion and electron-positron-ion plasmas immersed in a uniform magnetic field. Using the standard pseudopotential method, the magnetohydrodynamics (MHD) equations are exactly solved and a global allowed matching condition for propagation of kinetic solitary waves is derived. It is remarked that, depending on the plasma parameters, the kinetic solitons can be sub- or super-Alfv\'{e}nic, in general. It is further revealed that, either upper or lower soliton speed-limit is independent of fractional plasma parameters. Furthermore, the soliton propagation angle with respect to that of the uniform magnetic field is found to play a fundamental role in controlling the soliton matching speed-range.