Non-linear heat structures and modes of current transfer to hot arc cathodes

Summary form only given. Diffuse and spot modes of current transfer to hot arc cathodes are analyzed by means of a theory of non-linear external heating of finite bodies (Benilov and Pisannaya, 1988). The model considered is based on the assumption that the thickness of a near-cathode plasma layer in which the ion flux to the cathode is formed and which gives a main contribution to the total near-cathode voltage drop is considerably smaller than dimensions of the cathode and radius of cathode spots. Current transfer across this layer is locally one-dimensional is such conditions and the density of the heat flux from the plasma to the cathode surface may be considered, for a given voltage drop in the layer, as a function of the local surface temperature. Thus, one arrives at the problem of finding a temperature distribution in a body (cathode) heated by an external heat flux with a density that is a given non-linear function of a local surface temperature. (This function can be found elsewhere: Benilov, 1993, Benilov and Marotta, 1995). The geometry considered in this work is as follows. A cathode is in the form of a cylinder whose cross section is not necessarily circular. Joule heating inside the cathode is neglected. An energy flux comes to the bottom surface of the cathode from the adjacent plasma. The top of the cathode is maintained at a fixed temperature by external cooling, the lateral surface is thermally insulated.