Fabrication process and electrical characterization of direct current parallel micro-discharges in helium

Micro Hollow Cathode Discharges (MHCD) have been fabricated. They are round holes through 250 $\mu$m or 500 $\mu$m thick Nickel-Alumina-Nickel surfaces. The base surfaces are constructed from 7.5 X 7.5 cm alumina wafers, which are vacuum baked then coated with chromium and copper seed layers and finally patterned. Nickel film, 5-6 um thick, is then deposited on either side of the alumina wafer using the process of electroplating. Single and multi cavity micro discharges are then laser drilled with diameters ranging from 130 $\mu$m to 300 $\mu$m and spacing between the cavities ranging from 245 $\mu$m to 315 $\mu$m. Breakdown vs. pressure measurements show that smaller diameter cavities (130 $\mu$m) have higher breakdown voltages than cavities with larger diameter (300 $\mu$m). In addition, the difference between the breakdown voltage and the operating voltage is substantially larger. Current-voltage measurements for single hole MHCD devices indicates that they operate in the normal glow regime with decreasing discharge voltage as discharge current is increased.