The effect of electric field and other external controls on plasma spokes
The effect of electric field and other external controls on plasma spokes lead image
Many plasma-based devices operate on the partially magnetized E×B plasma configuration, which spontaneously forms light-emitting structures called rotating spokes. Those structures can cause anomalous electron transport and adversely affect operation. Understanding the mechanisms of spoke formation and identifying methods of controlling it is important for plasma applications.
Using a code they developed, Sengupta et al. simulated rotating spoke dynamics in this plasma configuration during discharge formation when the electric field is rapidly changing.
Their simulation showed strong alignment of the density gradient, and an electric field perpendicular to the magnetic field triggered the formation of a rotating spoke in the plasma. The wavelength and anomalous electron transport of the spoke depended on strength of the electric field. In strong fields, they saw spokes with long wavelengths and heavy anomalous electron transport. In weak fields, they saw shorter spokes and lower electron transport.
Comparing simulations with and without elastic electron scattering allowed the authors to see the slight effects caused by elastic collisions, such as a minor decrease in the growth rate of the rotating spokes. They found a reduction in neutral pressure, a parameter easily controlled externally, transformed short spokes back into long spiral spokes.
“Our work significantly advances the physics model for the spoke triggering mechanism or at least one of the mechanisms, their self-restructuring in the evolving discharge, and their dependence on externally controllable parameters such as neutral pressure,” said author Andrei Smolyakov.
Next, the authors will investigate the role of the localized ionization fronts produced by rotating spokes and how spokes respond to ion mixtures.
Source: “Restructuring of rotating spokes in response to changes in the radial electric field and the neutral pressure of a cylindrical magnetron plasma,” by M. Sengupta, A. Smolyakov, and Y. Raitses, Journal of Applied Physics (2021). The article can be accessed at https://aip.scitation.org/doi/full/10.1063/5.0049457 .
This paper is part of the open Physics of Electric Propulsion Collection, learn more here .
