A New Approach to High-Power Pulsed Glow Plasma Generation: Shunting Glow Plasma

Shunting discharge plasmas are metal plasmas that can be generated around a conductive rod at a reduced pressure on the order of 0.1-100 Pa. Even at atmospheric pressure, a plasma can be generated because the rod is heated to emit metal vapor so as to generate gas breakdown around the rod. When the temporally increasing voltage across the rod matches the plasma ignition voltage, a shunting plasma is ignited. The plasma ignition is triggerless and, thus, does not require an external signal. There are two types of shunting plasmas: glow and arc discharges, with sustenance voltages of approximately 100 and 60 V, respectively. The plasma results in an arc discharge via a glow state. When a pulsed-power source with a controlled pulse duration is used to obtain a glow plasma only, a stable steady-state glow can be obtained under a suppressed current with a duration of over 10 s and a consumed power of several tens of kilowatts. A shunting glow plasma can be realized by controlling the pulse duration. In this paper, optical emission spectra from the shunting glow and shunting arc are observed. Singly charged carbon ions were found to be produced by the glow plasma. Carbon emission was significant in a nitrogen gas environment, as compared with an argon environment. In the case of a shunting arc, the optical emission is broad in wavelength, and doubly ionized carbon species also arise. A preliminary test of diamond-like carbon (DLC) film deposition was carried out, where the DLC was deposited on a substrate set near a plasma source. The DLC state was determined using Raman spectroscopy, and no macroparticles were found on the deposited film, which had a clean surface. The rod holder used as an electrode showed no damage. In contrast, in the case of a shunting arc, many macroparticles were found on the deposited films, and serious damage to the electrode also occurred.