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A Non-Isothermal Theory of an Electrostatic Probe in a Weakly Ionized Gas,
PRINCETON UNIV N J GAS DYNAMICS LAB
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In the existing literature on the diffusion theory of the interaction between a weakly ionized plasma and a solid surface, the electron temperature is assumed to be constant. This assumption is dubious For an absorbing probe immersed in a plasma, asymptotic theoreis based upon the small Debye length can be developed with electron energy balance taken into consideration. Detailed development is given here for both the cases when ions are much colder than electrons and when the temperatures of the two charged species are of the same order. The main results are as follows 1 The current-voltage characteristics of the probe can be represented by an asymptotic series in which the leading term is the probe potential obtained under quasi-neutral approximation. 2 In general, the sheath scales are different from those obtained in isothermal theory and depend on the current or probe potential and the temperature ratio of the two charged species. 3 The cold ion approximation is valid only when the ion temperature is much lower than the electron temperature in both the quasi-neutral region and the sheath. 4 The ion current approaches the saturation value at a probe potential lower than that given by the isothermal theory. Author
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