HYBRID MODEL OF A RECTANGULAR HOLLOW-CATHODE DISCHARGE

A rectangular hollow cathode discharge was investigated by means of a two-dimensional self-consistent hybrid model combining Monte Carlo sim ulation of the motion of fast electrons and a fluid description of slo w electrons and positive ions. Our calculations were carried out for a cold-cathode de abnormal glow discharge in helium, operating at moder ate (similar to 1 mA/cm(2)) current densities and at low (similar to 1 mbar) pressures. The results demonstrate the existence of the hollow cathode effect in the discharge. On the other hand the energy distribu tion function of electrons indicates that a considerable number of fas t electrons is absorbed by the anode, representing a major loss for th e maintenance of the discharge. A significant fraction of primary elec trons (approximate to 5-20%) was absorbed by the anode before they wer e able to produce any ions. Due to the loss of high-energy electrons a t the absorbing anodes, ionization is less efficient than that in conv entional (e.g., cylindrical) hollow cathodes, thereby explaining the i ncreasing voltage-linear current density characteristics of the discha rge. Backscattering of high-energy electrons from the anodes significa ntly affects the discharge characteristics: a backscattering coefficie nt of 0.2 resulted in approximate to 90% increase of the He+ density a nd approximate to 60% increase of the linear current density at 2 mbar pressure and 300 V voltage.