Emission spectroscopic diagnostics in the cathode region of a high intensity arc

Summary form only given, as follows. Emission spectroscopic diagnostics have been carried out over a wide range of parameters in the cathode region of a high intensity arc. A specially designed plasma torch system has been set up for this investigation and an optical multi-channel analyzer (OMA) and a spectrometer system has been employed. Electron temperatures were obtained from the profiles of the Ar I and Ar II lines assuming PLTE. Electron number densities were derived from Stark broadening profiles of hydrogen Balmer lines, when 1% hydrogen was added to the argon plasma gas. The arc current has a small effect on the arc in the cathode region. The electron temperature as well as the electron number density increase slowly as the current increases. However, the pressure has a significant influence on the arc. Increase of pressure will constrict the arc, which will increase the electron number density and decrease the electron temperature at the arc center with steeper radial gradients of both. Adding about 30% hydrogen into the argon arc also constricts the arc in front of the cathode spot. This constriction has the same phenomena as the pressure constriction except an increasing electron temperature at the arc center. It is very interesting to find that the cathode shape strongly affects the electron temperature, but has little influence on the electron number density. These results provide us with a better understanding of the arc behavior in the cathode region and arc-cathode interaction.