Optical Properties of Arc Spot Plasma for Cleaning Oxide on the Steel Surface

The optical properties have been investigated in situ by optical emission spectroscopy and a high-speed camera for various cathode surfaces in low-pressure arc spot plasma. Electron excitation temperature (T-exc) is estimated by using the Fe I lines based on Boltzmann plot. It is found that cathode surfaces affect strongly on the discharge features of spot plasmas. T-exc increases with the arc current for both oxidized and clean surfaces, and T-exc is higher in the case of clean surfaces. Compared with the discharge on oxidized surface, the fluctuation of T-exc along with the intensity of emission lines enhances largely as spots move on a clean surface. The spots on oxidized surface present negligible change in trajectory in observation time, while spots move randomly in the temporal distribution for the clean surface. It is suggested that the presence of oxides on cathode surface strongly influences microexplosion processes on the cathode, and thus improve the stability for the spot plasma.