Hydrogen plasma induced photoelectron emission from metal surfaces

Abstract

Low temperature hydrogen plasmas are strong sources of vacuum ultraviolet radiation. The properties of laboratory plasmas can be influenced by surface processes induced by photons with their energies exceeding the surface work function of the wall material.

In this work, the plasma induced photoelectron emission has been studied with different ion sources. The emission depends on the mechanical design of the plasma device, plasma heating method and the discharge power (density). Parametric studies include the quantifying of the emission from different metal surfaces, commonly used as plasma facing materials in ion sources, as well as alkali metal covered surfaces. Experimental studies suggest that low temperature hydrogen plasma induced photoelectron emission from metal surfaces can reach an order of magnitude of 1 A per kW of plasma heating power. Furthermore, the emission can increase 2–3.5 times when the metal surface is coated with a thin layer of alkali metal reducing the work function. The free electrons produced by the photoelectron emission can influence various plasma processes and especially the plasma sheath structure, which has been studied using a one-dimensional analytical model.