Evolution of cathodic microprotrusions immersed in dense plasmas

A model has been developed to simulate the interaction between dense (order of n_e=10¹⁶ cm^-3) plasmas and the naturally occuring microprotrusions on cathode surfaces. Heating and cooling of an ellipsoidal two-dimensional (2-D) model microprotrusion is simulated in order to achieve the time-dependent behavior in terms of electron emission and erosion of the microprotrusion. Thermo-field emission is taken into account for the investigation of the electron emissivity of the tip. The 2-D model shows distinct differences to a one-dimensional (1-D) model in the scope of “ignition” of emissive and erosive behavior. In particular, it is found that due to ion heating, a 2-D protrusion can easily be ignited within ranges of plasma parameters and cathode voltage drop where 1-D models fail to explain the experimentally observed ignition of cathode spots on metal surfaces