Measurement of Electron Transport in High Density Gaseous Argon in Crossed Electric and Magnetic Fields

Abstract

In low density gases, where only classical single-scattering has to be regarded, it is found that the quantity μ D N which is the drift mobility μ D — given by the electron drift velocity u D in an electric field E by the relation μ D = E/u d — multiplied by the gas density N is a universal function of the reduced field E/N, i. e. independent of the gas density. At higher densities in a number of gases anomalous density effects have been observed [1, 2, 3, 4, 5, 6, 7, 8, 9], demonstrating the need for multiple scattering corrections. Several attempts [10, 11, 12, 13, 14], have been made to explain this density effect within Boltzmann transport theory by modifying the single electronatom scattering cross section in a density dependent way. These models were only partly successful and they in particular treat gases with positive and negative scattering lengths showing opposite density effects in a different way. For example for He, Ne (positive scattering length) μ D N decreases with increasing N while for Ar, Kr, Xe (negative scattering lenght) μ D N increases. Recently a phenomenological model has been put forward which explains both the negative density effect in Ne [15] and the positive density effect in Ar [16] in the same way. The main features of the model are a positive shift of the kinetic energy of the electrons in the dense medium and the consideration of correlations among scatterers by taking into account the static structure function. This model is able to explain the electric field dependence of the drift mobility data in Ar for densities up to N ≤ 70 · 1020 cm −3 [16].