A Study on Arc Instability Phenomena of a Hollow Cathode Plasma Torch in a Low Pressure Environment

Hollow cathode plasma system designs have been studied previously, but currently there is no commercial system available on the market that offers true axial injection in a single cathode configuration. Axial injection has the benefit of longer particle residence time in the plume, however,  the resulting arc instability phenomena accelerates wear and tear. This study investigates the arc instability phenomena in a modified hollow cathode plasma torch design under low pressure (20-80 Torr). Gun voltage measurements were used to evaluate stable and unstable regimes. For comparison purpose, arc fluctuations with a standard solid cathode torch design under identical operating parameters have been studied. A comparison of different internal hardware configurations is done to understand and establish important factors in design between the hollow and solid cathode systems. Further, this work presents a characterization of parameters that would exploit plume elongation and accelerated gas velocities under low pressure environment to stabilize the arc of the hollow cathode design.