Generation of Electrojets in Weakly Ionized Plasmas through a Collisional Dynamo

TL;DR

This paper introduces a universal criterion for the formation of electrojets in weakly ionized plasmas, linking neutral flows and magnetic fields, and highlights the role of a neutral-dynamo mechanism similar to classical current-driven magnetic field generation.

Contribution

It presents a new, conductivity-independent criterion for electrojet formation and clarifies the role of neutral-dynamo processes in plasma current generation.

Findings

Derived a universal criterion for electrojet formation.

Showed the neutral-dynamo acts like a DC current in magnetic field generation.

Simplified the criterion in cases where displacement current is negligible.

Abstract

Intense electric currents called electrojets occur in weakly ionized magnetized plasmas. An example occurs in the Earth's ionosphere near the magnetic equator where neutral winds drive the plasma across the geomagnetic field. Similar processes take place in the Solar chromosphere and MHD generators. This letter argues that not all convective neutral flows generate electrojets and it introduces the corresponding universal criterion for electrojet formation, $\nabla\times (\vec{U}\times\vec{B})\neq\partial\vec{B}/\partial t$, where $\vec{U}$ is the neutral flow velocity, $\vec{B}$ is the magnetic field, and $t$ is time. This criterion does not depend on the conductivity tensor, $\hat{\sigma}$. For many systems, the displacement current, $\partial\vec{B}/\partial t$, is negligible, making the criterion even simpler. This theory also shows that the neutral-dynamo driver that generates electrojets plays the same role as the DC electric current plays for the generation of the magnetic field in the Biot-Savart law.