Spectroscopic study of high current discharges

A high current arc was developed between carbon electrodes in H2, SF6, He, Ar, and air at an initial pressure higher than 1 atm. The current peak was above 5 kA and the duration of the current was 250 µs. The temporal and spatial changes of plasma parameters were measured by time-resolved spectrography and high-speed framing camera. The electron density of the plasma was estimated from the Stark broadening of the lines, Hβ, C II 4267 Å, He I 4471 Å, and He I 5876 Å. Our observations show the following: The arc space is divided into two regions, the bright narrow core and the broad outer flame. The electron density of the core is estimated to be of the order of 10¹⁸cm^-3and an electron temperature of the order of 10⁴°K is obtained at current peak. Even after current zero, the electron density keeps the order of 10¹⁷cm^-3regardless of the kind of gas.