Ions travelling in the cathode space charge zone: charge evolution and effect on the electron emission

In an arc root the emitted electron density at the cathode reaches very high values (up to 10/sup 8/ A/m/sup 2/). Academically, modellings of the cathode emission phenomena take into account the role of the cathode temperature and of the electric field. However, these effects cannot explain the very high electron current density in the case, for instance of a copper cathode. One has to consider the contribution of other effects such as the role on the electron emission of the ions (here, He/sup +/ ions) present near a copper cathode. This constitutes the object of this paper using the coupled angular modes method developed in particular to handle charge transfer processes between the cathode surface and the ions approaching the electrode. This method provides the energy levels and widths, for the excited states of neutral atoms. These results are then used in a rate equation describing the time evolution of the various ion and atomic level populations when the ion approaches the surface and providing the number of ejected electrons by this process.