An Effect of Positive Space Charge in Collector Analysis of Discharges

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Abstract
By use of a collector with mutually insulated sections to which different potentials could be applied, it has been shown, with a low voltage arc in argon, that under the special conditions of short collector and small electron concentration the positive ion sheath which forms on insulating surfaces near a collector in a plasma may lead to serious misinterpretation of the characteristics of the collector. The effect is twofold, first, a general diminution in the apparent concentration of electrons in the plasma, and, second, an apparent preferential suppression of the slowest electrons. Under most working conditions, these are probably inconsiderable at low pressure but perhaps important at a pressure of a few mm and higher. The collector characteristics obtained have been analyzed for Maxwellian distributions and by a method in which no initial assumption is made concerning the energy distribution other than that it is isotropic. A formula is given to facilitate double differentiation in the latter case.

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