Interaction of Biased Electrodes and Plasmas: Sheaths, Double Layers and Fireballs

TL;DR

This paper reviews recent advances in understanding how biased electrodes interact with plasmas, focusing on sheath structures, stability, and effects on plasma properties across various applications.

Contribution

It provides a comprehensive summary of the conditions, stability, and properties of different plasma sheath structures and their influence on plasma-electrode interactions.

Findings

Identification of conditions for sheath formation

Analysis of stability criteria for sheath structures

Impact of sheaths on plasma and boundary interactions

Abstract

Biased electrodes are common components of plasma sources and diagnostics. The plasma-electrode interaction is mediated by an intervening sheath structure that influences properties of the electrons and ions contacting the electrode surface, as well as how the electrode influences properties of the bulk plasma. A rich variety of sheath structures have been observed, including ion sheaths, electron sheaths, double sheaths, double layers, anode glow, and fireballs. These represent complex self-organized responses of the plasma that depend not only on the local influence of the electrode, but also on the global properties of the plasma and the other boundaries that it is in contact with. This review summarizes recent advances in understanding the conditions under which each type of sheath forms, what the basic stability criteria and steady-state properties of each are, and the ways in which each can influence plasma-boundary interactions and bulk plasma properties. These results may be of interest to a number of application areas where biased electrodes are used, including diagnostics, plasma modification of materials, plasma sources, electric propulsion, and the interaction of plasmas with objects in space.