3D simulations of positive streamers in air in a strong external magnetic field

TL;DR

This study uses 3D PIC-MCC simulations to analyze how strong external magnetic fields influence the behavior, branching, and structure of positive streamers in atmospheric pressure air, revealing magnetic field-induced deflections and radius reductions.

Contribution

The paper presents the first detailed 3D simulation analysis of positive streamer behavior in air under magnetic fields up to 40 T, highlighting magnetic effects on streamer deflection, branching, and radius.

Findings

Streamers deflect towards magnetic field directions, causing branching.

Stronger magnetic fields increase the angle between streamer branches.

Streamer radius decreases as magnetic field strength increases.

Abstract

We study how external magnetic fields from 0 to 40 T influence positive streamers in atmospheric pressure air, using 3D PIC-MCC (particle-in-cell, Monte Carlo collision) simulations. When a magnetic field $\vec{B}$ is applied perpendicular to the background electric field $\vec{E}$, the streamers deflect towards the $+\vec{B}$ and $-\vec{B}$ directions which results in a branching into two main channels. With a stronger magnetic field the angle between the branches increases, and for the 40 T case the branches grow almost parallel to the magnetic field. Due to the $\vec{E}\times\vec{B}$ drift of electrons we also observe a streamer deviation in the opposite $-\vec{E}\times\vec{B}$ direction, where the minus sign appears because positive streamers propagate opposite to the electron drift velocity. The deviation due to this $\vec{E}\times\vec{B}$ effect is smaller than the deviation parallel to $\vec{B}$. In both cases of $\vec{B}$ perpendicular and parallel to $\vec{E}$, the streamer radius decreases with the magnetic field strength. We relate our observations to the effects of electric and magnetic fields on electron transport and reaction coefficients.