Optimum operational conditions and microfabrications with UV lasers of very low-power DC micro-arcjets

Investigations on optimum operational conditions of very low-power DC micro-arcjet, or micro-plasmajet, were conducted. It was shown that with an electrically insulating material for a constrictor stable discharges below 5 W could be achieved. Also, microfabrication of micro-arcjet nozzles with fifth-harmonic Nd:YAG pulses (wavelength 213 nm) were conducted. Micro-arcjet nozzles were machined in a 1.2 mm thick quartz plate. Sizes of the nozzle exit were 0.44 mm in height and constrictor height of 0.1 mm. For an anode, a thin film of Au (∼100 nm thick) was coated in vacuum on divergent part of the nozzle. As for a cathode, an Au film was also coated on inner wall surface. In discharging operational tests, a stable discharge was observed for mass flow of 1.0 mg/s, discharge current of 6 mA, discharge voltage of 600 V or 3.6 W input power. In this case, plenum pressure of the discharge chamber was 80 kPa. Thrust obtained was 1.4 mN giving specific impulse of 138 s with thrust efficiency of 24% with 3.6 W input power.