Peculiarities of spatial relaxation of the mean electron energy in inert gases and their mixtures in a uniform electric field

Abstract

A theoretical study of the spatial relaxation characteristics of the mean electron energy in a uniform electric field in He, Ne, Ar, Kr, Xe and a mixture of He:Xe was performed. Calculations were carried out with the use of the Monte Carlo technique. Electrons were launched at some point z = 0, and the electron energy distribution function and the mean electron energy u m(z) were calculated at various distances from the source. According to calculations, for pure gases in a wide range of the electric field strength E, the dependence u m(z) has the form of damped oscillations. At that, the relaxation length L and the oscillation period Λ are almost independent of the form of the energy spectrum of the electron source. It is shown that for all pure gases the calculated dependences L(E) have the shape of a hump, and for each gas the position of the maximum corresponds to such E values at which the energy lost by electrons in elastic collisions is about 4%–8%. For the case of Xe we also studied the variation of L(E) depending on the set of cross sections used in the calculations. It was also shown that for the same E value, the relaxation length in He:Xe mixture differs significantly from that in pure He or Xe. Moreover, u m(z) in a certain range of parameters (E and percentage of Xe in the gas mixture) is characterized by the sum of two damped oscillations with different spatial periods.