Absence of Debye Sheaths Due to Secondary Electron Emission

TL;DR

This study uses particle-in-cell simulations to show that in plasmas with high secondary electron emission, classical Debye sheaths do not form, leading to unobstructed electron flow and the formation of inverse sheaths instead.

Contribution

It demonstrates the absence of classical Debye sheaths in plasmas with high secondary electron emission, introducing the concept of inverse sheaths and their effects.

Findings

No classical Debye sheath forms under high secondary emission.

Electrons reach the walls without repulsion, increasing fluxes.

Walls develop a positive charge, creating inverse sheaths.

Abstract

A bounded plasma where the electrons impacting the walls produce more than one secondary on average is studied via particle-in-cell simulation. It is found that no classical Debye sheath or space-charge limited sheath exists. Ions are not drawn to the walls and electrons are not repelled. Hence the plasma electrons travel unobstructed to the walls, causing extreme particle and energy fluxes. Each wall has a positive charge, forming a small potential barrier or "inverse sheath" that pulls some secondaries back to the wall to maintain the zero current condition.