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Experimental study of argon II line profiles in a pulsed arc plasma Neufeld, Carl Richard


Time-resolved spectrographic techniques were used to obtain the profiles of A II lines emitted from a laboratory plasma. For the dense, low-temperature plasma studied, most of the broadening of the observed lines results from interactions of the emitter with free charges in the surrounding plasma. The plasma was created by discharging a previously- charged lumped-parameter delay line through a specially- constructed vessel containing an argon-hydrogen mixture. By means of a rotating-mirror shutter, light from the discharge was admitted to the spectrograph during a time interval when the intensity of the A II lines was constant to within about 10%. This time interval was chosen after monitoring the time dependence of the intensity of several A II lines with a monochromator-photomultiplier combination. A calibration spectrum was also obtained with a seven-step neutral density wedge in order to determine the response of the photographic emulsion. Of the twenty-four measureable A II lines recorded, fourteen yielded profiles which could be treated by a Voigt analysis. In this way the profiles could be corrected for the effects of instrumental and Doppler broadening. The electron number density was determined from the widths of the lines in multiplet 6 of the A II spectrum, previously measured by other workers. The results indicate considerable disagreement with the original theory of line broadening as developed by Griem and his co-workers. The half-widths of the lines reported here are up to 4.0 times wider than predicted theoretically. The line shapes appear to be Voigt functions, rather than the predicted Lorentzian profiles. The measurements are in good agreement with those of other workers, where comparisons could be made. Measurements of some of the lines reported here do not appear to have been published elsewhere.

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