Dependence of the Properties of Moving Striations in the Plasma of the Positive Column on Some External and Internal Parameters
Dependence of the Properties of Moving Striations in the Plasma of the Positive Column on Some External and Internal Parameters
Factors affecting the self-excitation of low-frequency oscillations in an electric discharge
The influence of the individual factors affecting the production of low-frequency oscillations connected with moving striations in a discharge is analysed and experimentally verified. From the conception of two mechanisms of feedback, which leads to self-excitation of these oscillations, it follows that the following influence the production of oscillations: 1) the tendency of the plasma to stratification, 2) the length of the positive column, 3) processes in regions at the electrodes, 4) the external electric circuit.The measurements confirm the influence of all these factors. It is shown that the main factor conditioning the production of oscillations is the property of the plasma of the positive column — its tendency to stratification. The plasma of a glow discharge in neon — in the region of low pressures and currents investigated — has a very strong tendency to stratification with the exception of a small interval in the neighbourhood of the pressure of 4 mm Hg and current 3 тА. Low-frequency oscillations and moving striations are therefore very often present in a discharge in neon.The influence of the external circuit on the oscillations investigated was also experimentally proved, but it is very weak.
Moving Striations in Neon and Helium
During some work on Neon Lamps for Stroboscopic Work, it was noticed that, when the flash of an ordinary spectrum tube containing neon was analysed by a rotating mirror, it consisted of two parts, an extremely short flash followed by a flame or arc, and that the latter consisted of bright striations travelling from anode to cathode. The same phenomenon was observed with helium. The velocity of these striations was roughly measured, and found to be about 50,000 cm./sec. in neon and 100,000 cm./sec. in helium. As these figures approximated to the velocities of sound in these gases, it was hoped that investigation of the phenomenon might lead to an explanation of striations generally. This expectation has, unfortunately, not been realised, for these velocities were soon found to be special or limiting cases of far more complex phenomena. The following paper is an account of the preliminary experiments, which have given interesting, but somewhat inconclusive results. The first account of moving striations observed by means of a rotating mirror is given by A. Wullner.† They were investigated more fully by W. Spottiswoode. Both these observers used several elementary gases then available, but most of Spottiswoode’s results were obtained with compounds, these giving more definite striations. Unfortunately, neither observer recorded any figures for the velocities, but Wullner mentions that his mirror was rotated at ½ to 2 revolutions per second.