Heating of refractory cathodes by high-pressure arc plasmas: I

Abstract

A model of the near-cathode plasma layer in a plasma under a pressure of theorder of one or several bars is reconsidered on the basis of recenttheoretical results. Physics of the near-cathode layer is analysed in therange of near-cathode voltage drops of up to 50 V, in accord torecent experimental results which have shown that the near-cathode voltagedrop in high-pressure arc discharges may be that high. It is found that anon-monotony of the dependence of the energy flux density on the surfacetemperature at fixed values of the near-cathode voltage drop is caused byone of the three mechanisms: overcoming of the increase of combined ion andplasma electron heating by the increase of thermionic cooling as the plasmaapproaches full ionization; non-monotony of the dependence of the ioncurrent on the electron temperature which is caused by the deviation of theion current from the diffusion value; rapid increase of the plasma electronheating which is subsequently overcome by thermionic cooling. A closeddescription of the plasma-cathode interaction is obtained by numericallysolving the nonlinear boundary-value problem for the temperaturedistribution inside the cathode body. Results of numerical modelling of thediffuse discharge under conditions of a model arc lamp are given and a goodagreement with the experimental data is shown.