Plasma Waves and Jets from Moving Conductors

TL;DR

This paper develops a covariant formalism to analyze plasma waves generated by moving conductors in magnetic fields, revealing how fluid motion influences wave types and jet formation, with applications to pulsar outflows and neutron star jets.

Contribution

It introduces a spacetime-covariant framework for plasma wave perturbations caused by moving conductors, including closed-form solutions for incompressible flows and insights into jet dynamics.

Findings

Fast-mode waves are driven by fluid compressibility.

Incompressible flows produce pure-Alfvén outflows.

Magnetic field carries flow information at light speed.

Abstract

We consider force-free plasma waves launched by the motion of conducting material through a magnetic field. We develop a spacetime-covariant formalism for perturbations of a uniform magnetic field and show how the transverse motion of a conducting fluid acts as a source. We show that fast-mode waves are sourced by the compressibility of the fluid, with incompressible fluids launching a pure-Alfv\'en outflow. Remarkably, this outflow can be written down in closed form for an arbitrary time-dependent, nonaxisymmetric incompressible flow. The instantaneous flow velocity is imprinted on the magnetic field and transmitted away at the speed of light, carrying detailed information about the conducting source at the time of emission. These results can be applied to transients in pulsar outflows and to jets from neutron stars orbiting in the magnetosphere of another compact object. We discuss jets from moving conductors in some detail.