DISSOCIATIVE RECOMBINATION IN CASCADED ARC GENERATED AR-N2 AND N2 EXPANDING PLASMA

The expanding plasma obtained from a cascaded arc thermal source is an alyzed with double probe, mass spectrometric, and Faraday cup measurem ents. In the argon-nitrogen mixtures a decrease in ion fluence is obse rved, contrary to pure argon plasmas in which recombination is insigni ficant. The recombination in argon-nitrogen plasmas is caused by charg e exchange between atomic ions and N2 molecules followed by dissociati ve recombination. Hence, these processes account for the enhanced axia l decay of the plasma density and also for the change in the ion mass spectra of the ion beam extracted from the expanding plasma. The total ion beam current density is also governed by charge exchange followed by dissociative recombination and is thus dependent on the recirculat ing neutral molecules.