Tearing of charged current layers

TL;DR

This study uses PIC simulations to explore how charged current layers in astrophysical plasmas, like pulsar winds, undergo tearing instability and plasmoid formation, revealing the influence of charge, temperature, and Bernstein waves.

Contribution

It demonstrates the complex interplay between electrostatic Bernstein waves and tearing modes in charged current layers, highlighting effects of charge and temperature on instability growth.

Findings

Charged Harris sheets generate trapped Bernstein waves affecting tearing dynamics.

Charge density fluctuations develop in initially uncharged rotational layers.

Tearing rate increases significantly under certain parameters in charged configurations.

Abstract

Astrophysical current layers, e.g., in pulsar winds, can be electrically charged, while the plasma is charge-symmetric, $e^\pm$. Using PIC simulations, we investigate dynamics and plasmoid formation (tearing instability) in charged Harris-type and rotational current layers. Electrically charged current layers, initially in global force-balance, are electrostatically unstable: the resulting dynamics is an intricate interplay between electrostatic Bernstein waves (BWs) and the current tearing mode. Besides overall density and magnetic field, plasma temperature is an important factor. In the charged Harris sheet set-up, the quickly generated BW are trapped within the layers (internally reflected at the upper hybrid resonance). BWs quickly redistribute the charge modifying the initial stage of tearing, but without strongly affecting overall plasmoid growth; resulting plasmoids are mildly charged. In rotational current layers: (i) even initially overall uncharged configurations develop large fluctuations of charge density; (ii) overall dynamics depends on the initial overall temperature; (iii) for certain combination of parameters tearing rate is greatly increased in the charged case.