Examination of Excitation Temperature of Vacuum Arc Based on Collisional-Radiative Model

The excitation temperature is a widely measured plasma parameter. In this article, the validity of an excitation temperature measurement is verified using a transition simulation between excited levels based on a collisional-radiative model. The collisional-radiative model calculation was validated by comparing it with the results of a spectroscopic measurement for a 2-kA peak vacuum arc ignited between the Cu100, Cu80Cr20, and Cu50Cr50 electrodes, whose diameter and gap length are 10 and 5 mm, respectively. As a result, the experimental result of the spectroscopy can be well simulated using the collisional-radiative model when the electron temperature and electron density are set to approximately 1.1–1.2 eV and 1.3– $2.1\times 10^{20}\,\,\text{m}^{-3}$ , respectively. It was found that the excitation temperature can be obtained from only two lines (510.6- and 515.3-nm lines) of the Cu I spectra with an accuracy comparable to that obtained from many line spectra of Cu neutrals. In addition, the relaxation times of the two lines are shorter than 100 ns. The excitation temperature, the electron temperature, and the electron density of the Cu100 electrodes were slightly higher than those of Cu50Cr50 electrodes. Such dependence on electrode material is caused by the difference in the density of the neutrals and ions. A comparison of the deposition ratio of Cu and Cr on the viewing port glass measured using energy-dispersive X-ray spectroscopy and a comparison of the cathode spot number suggest that the difference in the density of the neutrals and ions is caused by the difference in the cathode spot current.