Striations in the positive column of an argon glow discharge

Abstract

A study of the influence of the electrodes, discharge length, current, and a magnetic field on the characteristics of moving and standing striations in a low pressure DC argon glow discharge indicated that the cathode was of major importance. The anode evidently had little or no effect. Changes in discharge tube current and discharge length merely expanded or compressed the striation responses in time and/or in space; the sequence of events was not altered. The magnet produced a local effect in the vicinity of the magnet similar to an increased discharge length. All observations were made at a pressure of two mm of mercury with an H shaped tube containing four electrodes. Standing and moving striations both were always evident when a stable operating mode was present. There was, then, the rather unusual situation of moving striations moving through standing striations always present. It was found that the moving striations seemed to have a maximum velocity just before they reached the head (cathode side) of a standing striation, and a minimum velocity immediately after passing through the head of the standing striation. A very strong indication was found of a phase difference of 0 from to 15 microseconds between the 7500 A⁰ lines (red) and the 4200 A⁰ lines (blue) of the moving striations, with the blue line appearing first. This result appears to be contrary to extant theory and previous results at 12 mm of argon.