DC magnetic field generation in unmagnetized shear flows

TL;DR

This paper predicts and confirms through simulations that unmagnetized shear flows in plasmas can generate long-lived DC magnetic fields due to thermal effects or Kelvin-Helmholtz instability, with detailed kinetic modeling.

Contribution

It introduces a kinetic model for DC magnetic field generation in unmagnetized shear flows and validates it with particle-in-cell simulations, highlighting the formation and characteristics of these fields.

Findings

Long-lived magnetic fields form along shear layers.

Magnetic field magnitudes reach significant levels.

Fields have transverse width on electron length scale.

Abstract

The generation of DC magnetic fields in unmagnetized plasmas with velocity shear is predicted for non relativistic and relativistic scenarios either due to thermal effects or due to the onset of the Kelvin-Helmholtz instability (KHI). A kinetic model describes the growth and the saturation of the DC field. The predictions of the theory are confirmed by multidimensional particle-in-cell simulations, demonstrating the formation of long lived magnetic fields ($t \sim 100s \omega_{pi}^{-1}$) along the full longitudinal extent of the shear layer, with transverse width on the electron length scale ($\sqrt{\gamma_0}c/\omega_{pe}$), reaching magnitudes $eB_{\mathrm{DC}}/m_ec\omega_{pe}\sim \beta_0\sqrt{\gamma_0}$.