Diffusion and Elastic Collision Losses of the ``Fast Electrons'' in Plasmas

Abstract

(I) When the energy spectrum of plasma electrons consists of two clearly separable groups—a high‐energy, primary, non‐Maxwellian, and a low‐energy, secondary, Maxwellian one—the characteristic linear part of the corresponding probe curves, extrapolated to plasma potential, directly determines the random current density of the fast group. With a hemispherical anode and a hollow hot cathode near its center, in Ne of about 1 mm Hg pressure, the flow of the fast group at low diode currents follows closely the spherical case of diffusion. The experimental data, by means of the diffusion law, can be evaluated for the mean free path l of the fast electrons. It is found that l is independent of the plasma density and is about equal to the value calculated from the cross‐section function for 10–16 volt electrons in Ne. (II) The Diffusion law being applicable, the elastic collision losses of the fast group can be calculated. They are found to be relatively small compared to the total energy losses of the fast electrons. The results will be used in an attempt to determine the energy transfer from the fast group to the Maxwellian group, to be described in a subsequent paper. The most remarkable result is the low interaction of the fast group with the Maxwellian group at low total plasma densities where the partial density of the slow group is always comparable to or even much higher than that of the fast group.