Dominant spectra of background radiation in a SF6 post-arc channel

Composition of background spectra radiated from a SF₆ post-arc channel after current zero was investigated. The radiation intensity of the background spectra at a wavelength of 455 nm around zero current was measured. The post-arc temperature was estimated from the intensity ratio of two spectral lines at 426.0 and 442.7 nm of iron used as an electrode material. The emission coefficients of not only the continuous spectra but also the S₂ spectra due to the B³ Σ_u^--X³Σ_g ^- transition were theoretically calculated as a function of temperature in the range of 3000-6000 K. The results indicated that the background spectra mainly consist of continuous spectra at temperatures above 4500 K, and of S₂ spectra at temperatures below 4500 K. The temperature dependence of the calculated emission coefficients of the background spectra agreed fairly well with that of the measured radiation intensity