Measurements of the longitudinal diffusion coefficient and the drift velocity for electron swarms in hydrogen and nitrogen using a time-of-flight technique

Abstract

A time-of-flight technique has been developed to measure accurately the longitudinal diffusion coefficient (D_L) and the drift velocity (v) for electron swarms drifting and diffusing through uniform electric fields at high E/N.A pulse of electrons is released at the cathode, and a ‘box-car’ detector system is used to record the anode current distribution. The drift velocity is obtained from the mean delay time, and the longitudinal-diffusion coefficient is obtained from the standard deviation of the distribution.Results have been given for both hydrogen and nitrogen gas for the range 3 ≤ E/N ≤ 43 Td (1 Td = 10⁻²¹ Vm²). The values for the drift velocity are in good agreement with theory, whereas the values for D_L have revealed inadequacies in the present theoretical values for nitrogen.