Simple Way to Obtain the Velocity Distribution of the Electrons in Gas Discharge Plasmas from Probe Curves

Abstract

Until now no simple technique of determining the velocity‐ or energy‐distribution function of the electrons in gas discharge plasmas was known. Here a method of quickly finding this function from probe curves (preferably automatically plotted ones) is described. It is shown that for a given probe current‐voltage curve J(U) the energy distribution function g(U) of the electrons is proportional to a simple function which may be graphically determined from J(U). This function is U^−½ΔJ₀/ΔU, where ΔJ₀ is the distance between the intersections of the two tangents to the probe curve J(U) at the ends of the voltage interval ΔU with the current axis, and U is the (retarding) voltage in the middle of ΔU. It can be used for a determination of the energy distribution g(U) in a simple and straightforward one‐step procedure which is faster and in practice more accurate than the two‐step procedure previously used for finding g(U) by means of ∂²J/∂U². A set of probe curves which stem from a Maxwellian distribution is evaluated in both the conventional and the new way. The electron temperatures obtained check excellently. A set of probe curves from strongly non‐Maxwellian distributions in a Ne fireball discharge is evaluated. The presence of a fast and a slow group of electrons is revealed. The results are interpreted to some extent. Errors and dependability are discussed.