Energies of electrons in plasmas

Abstract

Though certain electric properties of flames. have been studied for more than one hundred years, until recently the origin of their electric conductivity had remained obscure. A quantitative treatment started with the advent of the thermal ionization theory by Lindemann and Saha. This theory gives the degree of ionization and the concentration of charges as a function of the temperature, provided the gas composition is known. The equation, seldom used in its complete form, is only valid for a system in thermodynamic equilibrium, and it was thought to be applicable to the case of a flame gas. The assumption was tested by electric probe gas temperature measurements; however, the use of single or double probes was originally confined to concentration measurements. Later doubts arose about the correctness of the assumption that gas, electron and excitation temperatures heave the same value. In recent years electron temperatures : (mean electron energies) have been investigated by means of probes in different flames of various compositions and types. Satisfaction was expressed whenever the values of the gas and electron temperature were the same and dissatisfaction, or doubt as to the correctness of the measurements, when the temperatures differed. Hopes to obtain a better insight into the physical phenomena by varying the gas pressure of the flame gas remained and thus the saturation ion current io Should become smaller, However, the slope (di/dv) of the probe curve is reduced to a much greater extent: firstly the electron mobility is reduced in the denser gas. Secondly the electron flow is controlled by diffusion towards and drift away from the probe surface hence a given change in voltage should produce in the danger gas a smaller change in electron current and thus the slope decreases strongly. The apparent electron temperature can therefore be smaller with cold The electron emission from hot probes has to be considered. If electrons are emitted from a probe which is negative with respect to the flame plasma, the probe current is increased because the ion current is now not only carried by positive ions to the probe but also by electrons moving away from the probe. The effect on the electron temperature may be small because both the saturation current, extrapolated to zero voltage, as well gg the slope of the current voltage at the origin rise. Small differences in the temperatures of the two probes | may be responsible for setting up a potential difference due to the calorelectric effect. [...]