The Topology of Canonical Flux Tubes in Flared Jet Geometry

TL;DR

This paper introduces a flux tube framework based on canonical vorticity to better understand plasma jet topology beyond traditional MHD, revealing new insights into jet collimation and helicity evolution.

Contribution

It extends magnetic flux tube concepts to include finite particle momentum, enabling visualization of plasma jets in regimes beyond MHD and linking canonical vorticity to observable jet features.

Findings

Finite ion momentum can produce long, collimated canonical vorticity flux tubes.

Canonical vorticity flux tubes can differ from magnetic flux tubes in flared geometries.

Helicity calculations show ion flows can unwind magnetic twist.

Abstract

Magnetized plasma jets are generally modeled as magnetic flux tubes filled with flowing plasma governed by magnetohydrodynamics (MHD). We outline here a more fundamental approach based on flux tubes of canonical vorticity, where canonical vorticity is defined as the circulation of the species canonical momentum. This approach extends the concept of magnetic flux tube evolution to include the effects of finite particle momentum and enables visualization of the topology of plasma jets in regimes beyond MHD. A flared, current-carrying magnetic flux tube in an ion-electron plasma with finite ion momentum is thus equivalent to either a pair of electron and ion flow flux tubes, a pair of electron and ion canonical momentum flux tubes, or a pair of electron and ion canonical vorticity flux tubes. We examine the morphology of all these flux tubes for increasing electrical currents, different radial current profiles, different electron Mach numbers, and a fixed, flared, axisymmetric magnetic geometry. Calculations of gauge-invariant relative canonical helicities track the evolution of magnetic, cross, and kinetic helicities in the system, and show that ion flow fields can unwind to compensate for an increasing magnetic twist. The results demonstrate that including a species finite momentum can result in a very long collimated canonical vorticity flux tube even if the magnetic flux tube is flared. With finite momentum, particle density gradients must be normal to canonical vorticities, not to magnetic fields, so observations of collimated astrophysical jets could be images of canonical vorticity flux tubes instead of magnetic flux tubes.