Plasma transport and optical flares in high-density plasmas produced from a pulsed cathodic arc

The development of a pulsed cathodic arc system capable of delivering plasmas with average ion charge densities up to 1019 e+/m3 at the substrate has enabled us to examine plasma transport and sheath dynamics in very high density drifting plasmas. The plasma is generated using pulsed cathode currents of 3 kA and passed through a quarter torus open-wound macroparticle filter. Using a titanium cathode, very high deposition rates (≤0.3 nm/500 μs pulse) have been achieved, producing pulsed plasmas that are 100–1000 times denser than the plasmas typically produced in dc arcs. For a given set of conditions, the net plasma current, as measured by a series of Rogowski coils in the filter duct, remained relatively constant along the length of the duct. The net current decreased rapidly as the bias on the substrate was varied from positive to negative, and also when the diameter of a negatively biased substrate was increased. Ion deposition trends in the opposite direction to the net plasma current because the overwhelming majority of charge carries are electrons. We observed illuminations produced near the substrate as the plasma impinged on its surface. These optical flares were emitting at wavelengths characteristic of neutral titanium (TiI). Our investigations indicate that the spatial distribution of the flares is not related to the position of the sheath at the substrate. However, the flares do carry information about the distribution patterns of excited and sputtered atoms and ions.