Spectrographic Measurements on an Arc Discharge

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Abstract
An arc discharge of 60-μsec duration and peak current of 2×104 A in an initial pressure of 3 Torr of helium was studied spectroscopically. Time resolution was obtained by Kerr cell shuttering a 1.5-m spectrograph. The spectra were analyzed by Stark broadening and line-to-line intensity ratios. The arc was found to quickly evolve many times the initial density in wall and electrode materials, to decrease in degree of excitation after the first 10 μsec, and to lack thermodynamic equilibrium. The doubly ionized species were found to have roughly consistent temperatures of 7±1.5 eV and the singly ionized species 4±1.5 eV. The ratio between the two populations was more appropriate to excitation energies of 1 or 2 eV.