Improvements to the microcavity hollow cathode source are reported. These include a lower breakdown voltage and a larger operating range of fill-gas pressures of argon, helium, and mixtures of each. Data showing the effect of size, shape, and materials (copper and stainless steel) of the cathodes and anodes on the breakdown voltage are presented. The minimum discharge current required for the discharge to enter the cathode cavity is profoundly affected by the size of the cathode cavity.
Yixin Chen and J. C. Williams, "Breakdown Characteristics in Argon-Helium Mixtures Using an Improved Microcavity Hollow Cathode Emission Source," Appl. Spectrosc. 50, 234-240 (1996)