A cathode spot model and its energy balance for metal vapour arcs

A non-stationary cathode spot model is proposed which is based on an interpretation of experimental data recently obtained. The significance of ion mass generation by Joule heating and the separation of energy flows associated with electron and ion currents in the cathode spot are the main differences with other known cathode spot models. The ion energy balance at the metal-vacuum transition is evaluated quantitatively and applied to a calculation of the ion fraction in the cathode current. For a broad range of metals and independent of the electron emission mechanism, minimum and maximum ion current fractions are found of around 10% and 20% respectively.

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