The measurement of electron transport coefficients in methane by a double-shutter drift tube method combined with ATS analysis

Three important transport coefficients, namely the ratio of the Townsend first ionization coefficient to the gas number density , the mean-arrival-time drift velocity and the product of the longitudinal diffusion coefficient and the gas number density , in methane have been experimentally determined over a wide range of E/N, E being the electric field and N the gas number density, from 0.2 to 2000 Td by a double-shutter drift tube method analysed by an arrival-time-spectrum (ATS) technique. Equilibrium of the electron energy at high values of E/N in the present experiment is confirmed by a Monte Carlo simulation for the same gas. The present values of and as a function of E/N agree well with those in the literature which were obtained by using techniques such as the steady-state Townsend experiment, time-of-flight analysis and a pulse experiment. This demonstrates the validity of the present drift tube method and ATS analysis. The present result for , however, agrees with that in the literature in the rough shape of variation with E/N only; it is found that there are differences of a few tens of percentage in the present values against the values in an earlier paper and that a local maximum and minimum found in the previous article do not exist.