Dissipation and particle acceleration in astrophysical jets with velocity and magnetic shear: Interaction of Kelvin-Helmholtz and Drift-Kink Instabilities

TL;DR

This study uses 2D PIC simulations to explore how combined velocity and magnetic shear in astrophysical jets trigger Kelvin-Helmholtz and Drift-Kink instabilities, leading to turbulence and efficient nonthermal particle acceleration.

Contribution

It demonstrates the nonlinear interaction between KH and DK instabilities in relativistic pair plasmas, revealing enhanced dissipation and particle acceleration mechanisms.

Findings

DKI disrupts KH vortices, creating turbulence.

Combined shear enhances energy dissipation.

Efficient nonthermal particle acceleration observed.

Abstract

We present 2D particle-in-cell simulations of a magnetized, collisionless, relativistic pair plasma subjected to combined velocity and magnetic-field shear, a scenario typical for astrophysical black-hole jet-wind boundaries. We create conditions where only the Kelvin-Helmholtz (KH) and Drift-Kink (DK) instabilities can develop, while tearing modes are forbidden. We find that DKI can effectively disrupt the cats-eye vortices generated by KHI, creating a turbulent shear layer on the DK timescale. This interplay leads to a significant enhancement of dissipation over cases with only velocity shear or only magnetic shear. Moreover, we observe efficient nonthermal particle acceleration caused by the alignment of the instability-driven electric fields with Speiser-like motion of particles close to the shear interface. This study highlights the sensitivity of dissipation to multiple simultaneous instabilities, thus providing a strong motivation for further studies of their nonlinear interaction at the kinetic level.