High Density Cascaded Arc Produced Plasma Expanding in a Low Pressure Region

Abstract

Experimental measurements made in thermal expanding argon, nitrogen and hydrogen plasmas with particular reference to molecular kinetics, surface nitriding and intense flux in magnetic field are discussed. The plasma is generated in a cascaded arc source. In the presence of molecular species (H2 / N2) dissociative recombination reactions involving rovibrationally excited molecules contribute to a rapid decay of the plasma species, especially for hydrogen system. A combination of nitrogen and hydrogen plasma gives an efficient plasma nitriding process, which has been applied for case hardening of machinery components. In another setup a strong axial magnetic field (0.4 -1.6 T) contains and substantially prolongs the plasma beam in the chamber. In the presence of the magnetic field, an additional current drawn through the plasma beam using a biased substrate and a ring creates dense low temperature plasma giving a new unexplored plasma regime. The plasma kinetics are modified in this regime from the recombining to the ionising mode. When the additional current in the argon plasma beam exceeds 30 A, its light emission is predominantly in the blue region. With the additional current and magnetic field, the emission intensity of H β and other lines arising from higher energy levels in the hydrogen Balmer series is enhanced.