A spectroscopic investigation of an argon glow discharge

Abstract

The visible spectrum from argon glow discharges was observed by means of a three-meter concave-grating spectrograph. The discharges were operated under various conditions: with moving striations in the positive column and without striations, and in the presence and absence of a helical instability. The principal results are as follows. No argon ion spectrum was observed at any position in the tube. No changes in the spectrum from the positive column were observed with changing operating conditions. Electrode materials were observed as impurities in the discharge near the electrodes. The helical instability was induced by a longitudinal magnetic field. An investigation of the critical field, which was required to initiate the instability, as a function of tube current, tube diameter and gas pressure, indicated that the critical field was sensitive to changes in all three parameters and to the transition of the discharge from the striated to the striation-free condition. A study of the feasibility of detection of a Doppler shift revealed that the longitudinal velocity of radiating atoms could be detected by crossing a Fabry-Perot interferometer with a prism spectrograph if the atom velocity was equal to or greater than the observed striation velocities.