The physics of non-thermionic cathodes of electric arcs

It is proposed that the process of electron emission from non-thermionic cathodes of electric arcs in inert gases is by the impact at the cathode of excited neutral states, both metastable and radiative. Electron production at the cathode by other processes such as by ionization in the cathode sheath, field emission, impact by positive ions or photoelectric emission appear to be inconsistent with the low arc voltages that are observed for arcs with non-thermionic cathodes, for example the voltages of ~ 25V such as occur for the arcs used for ¿Metal Inert Gas¿ welding.