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 alpha(T)/N, the mean-arrival-time drift velocity W-m and the product of the longitudinal diffusion coefficient and the gas number density NDL, 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 Carte simulation for the same gas. The present values of alpha(T)/N and W-m 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 NDL, 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 NDL values against the values in an earlier paper and that a local maximum and minimum found in the previous article do not exist.