Spatial density profiles of metallic ions with different charge states from a vacuum arc operated with background gas

A theoretical study of the ion density profiles resulting from the interact ion between metallic plasma ejected from cathode spots and background neutr al gas is presented. The model includes four different charge-state species for the metallic particles and also the gaseous ions, and a set of coupled continuity and momentum equations is solved. The electric field profile in the neutral plasma region (that is, outside the spot structure) is also ob tained. The main included atomic processes are elastic collisions between h eavy particles and neutral molecules, charge exchange between metallic ions and neutral gas and ionization and recombination (dissociative) of the gas by electrons. A simplified equation for the temperature of the metallic pa rticles is also solved in order to evaluate the pressure gradient force on the metallic neutrals generated by charge-exchange processes. Solutions for the profiles of the physical quantities involved in the probl em are presented for a non-filtered copper arc with a discharge current of 100 A running in an oxygen ambient with background pressure values in the r ange 10(-4)-5 Pa. The relative weight of the different atomic processes is also studied as a function of the gas pressure.