Linear and nonlinear evolution of current-carrying highly magnetized jets

TL;DR

This study uses high-resolution 3D simulations to analyze the linear and nonlinear evolution of highly magnetized, current-carrying jets, revealing how instabilities influence jet structure, energy dissipation, and momentum redistribution.

Contribution

It provides a detailed comparison between simulation results and linear theory, highlighting the nonlinear development and turbulence in magnetized jets with variable pitch profiles.

Findings

Large-scale helical deformations due to CDI growth

Good agreement between simulations and linear theory

Jet turbulence and energy dissipation during nonlinear phase

Abstract

We investigate the linear and nonlinear evolution of current-carrying jets in a periodic configuration by means of high resolution three-dimensional numerical simulations. The jets under consideration are strongly magnetized with a variable pitch profile and initially in equilibrium under the action of a force-free magnetic field. The growth of current-driven (CDI) and Kelvin-Helmholtz (KHI) instabilities is quantified using three selected cases corresponding to static, Alfvenic and super-Alfvenic jets. During the early stages, we observe large-scale helical deformations of the jet corresponding to the growth of the initially excited CDI mode. A direct comparison between our simulation results and the analytical growth rates obtained from linear theory reveals good agreement on condition that high-resolution and accurate discretization algorithms are employed. After the initial linear phase, the jet structure is significantly altered and, while slowly-moving jets show increasing helical deformations, larger velocity shear are violently disrupted on a few Alfven crossing time leaving a turbulent flow structure. Overall, kinetic and magnetic energies are quickly dissipated into heat and during the saturated regime the jet momentum is redistributed on a larger surface area with most of the jet mass travelling at smaller velocities. The effectiveness of this process is regulated by the onset of KHI instabilities taking place at the jet/ambient interface and can be held responsible for vigorous jet braking and entrainment.