Ionic Analysis of Cataphoresis in He–Ne Mixtures

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Abstract
For studies of cataphoresis in He–Ne mixtures, an analytic expression is derived for the functional dependence of the neon atoms in the axial direction. The analysis, which involves the continuity equation, considers the production and loss mechanisms of the Ne+ ions. The present theory can be used to predict the degree of ionization of neon at a given pressure and current, when the appropriate rate coefficients are known. In addition, techniques for ion sampling from gaseous plasmas have been used in the present investigation. Measurements have been made in commercial helium‐gas samples having a quoted neon concentration ≤0.001% and in samples containing 0.05% neon. Studies were conducted over a pressure and current range of 7–30 Torr and 8–80 mA, respectively. Depending on the experimental conditions, the following ions were observed: He2+, Ne+, Ne2+, and HeNe+. For the case of HeNe+, the present studies permit an estimate of the rate coefficient for the reaction Ne++2He→HeNe++He which is comparable to values obtained from afterglow studies. Measured values of the degree of ionization are in good agreement with values calculated using the present theory.