ANALYSIS OF THE INTERACTION OF CATHODE MICROPROTRUSIONS WITH LOW-TEMPERATURE PLASMAS

On real cathode surfaces which are in contact with plasmas, micrometre -sized protrusions are abundant. A two-dimensional numerical model has been developed to investigate the interaction of such a cathodic micr o-tip with a low-temperature plasma. The model allows integration and analysis of the various physical effects and an evaluation of their sp ecific role in the heating, emission and erosion of cathode surfaces. In particular, the influence of heating due to the intense ion flux fr om the plasma sheath onto the cathode surface has been investigated in detail. Special attention was paid to the simultaneous action of stro ng electric fields in the cathode fall region. The plasma-cathode inte raction is analysed for a range of parameters typical for high-current -density, low-pressure gas discharges and vacuum arcs. The temporal ev olution of the thermophysical properties of the micro-tip, its interac tion with the resulting metal vapour and its shape are modelled on a n anosecond time scale. Special cases of the evolution of microemitters have been identified, such as quasi-stationary emission on a microseco nd time scale and extremely fast, explosive-like behaviour with emitte r lifetimes on a nanosecond time scale. It is found that ion bombardme nt heating plays an essential part in the inception of emissive and er osive behaviour for a wide range of parameters.