Field to thermo-field to thermionic electron emission: A practical guide to evaluation and electron emission from arc cathodes

This work is concerned with devising a method of evaluation of electron emission in the framework of the Murphy-Good theory, which would be as simple and computationally efficient as possible while being accurate in the full range of conditions of validity of the theory. The method relies on Pade approximants. A comparative study of electron emission from cathodes of arcs in ambient gas and vacuum arcs is performed with the use of this method. Electron emission from cathodes of arcs in ambient gas is of thermionic nature even for extremely high gas pressures characteristic of projection and automotive arc lamps and is adequately described by the Richardson-Schottky formula. The electron emission from vaporizing (hot) cathodes of vacuum arcs is of thermo-field nature and is adequately described by the Hantzsche fit formula. Since no analytical formulas are uniformly valid for field to thermo-field to thermionic emission, a numerical evaluation of the Murphy-Good formalism is inevitable in cases where a unified description of the full range of conditions is needed, as is the general case of plasma-cathode interaction in vacuum arcs, and the technique proposed in this work may be the method of choice to this end. (C) 2013 AIP Publishing LLC.