Imaging of a localized hollow cathode discharge

In this paper, we present the image of a localized hollow cathode discharge (HCD) in argon. There are two ways for the onset of hollow cathode effect in HCD according to the pD value (i.e., product of pressure and cathode diameter). The overlapping of opposite negative glow regions can evolve from a weak solid plasma column at a lower pD value or evolve from a ring-shaped column at a higher pD value.