Electrical and optical characterization of a cage discharge plasma device for surface processing

Abstract

In this study, we developed a cage discharge plasma device, which generates a uniformly axially elongated negative glow plasma. The device is equipped with six stainless steel rod-shaped cathode electrodes and anodes distributed consecutively along the discharge chamber. Electron temperature (Te) and electron energy distribution functions (EEDFs) were measured using single and double electric probes under different experimental conditions. Single-probe measurements confirmed the existence of high- and low-energy groups of electrons. For both of these groups, Te peaks near the edge of the electrode and decreases sharply as the electrons move radially toward the edge of the negative glow region. Optical emission spectroscopy (OES) was used to calculate Te by applying the intensity ratio of the helium emission lines. The calculated Te using OES is generally in agreement with Te of the high-energy group measured by a single probe. On the other hand, the Te measured by the double probe was mostly consistent with Te of the low-energy group measured by the single probe. Ion densities measured with single and dual probes increased sharply near the cathode until reaching a point approximating the thickness of the cathode sheath and then increased slightly to reach a maximum value (∼1.6 × 109 cm−3) in the center of the discharge tube. EEDFs have been determined at different gas pressures, discharge currents, and radial positions, using single-probe technique. The density of the low-energy group increases, and the peaks move to lower energies in the direction of the center of the tube.