COMPUTER-SIMULATION STUDY OF CORRESPONDENCE BETWEEN EXPERIMENTAL AND THEORETICAL ELECTRON-DRIFT VELOCITIES IN CH4 GAS

Electron drift velocities for CH4 gas determined by Monte Carlo simulations of Schlumbohm's and Frommhold's experiments, in which drift velocity is defined by the gap length divided by electron transit time, are compared with theoretical drift velocities such as the diffusion-modified drift velocity V(d) of the steady-state Townsend, the average drift velocity of electrons W(v) of the pulsed Townsend, the centre-of-mass drift velocity W(r) and mean-arrival-time drift velocity W(m) of the time-of-flight experiments when ionization is appreciable. The results show that the drift velocities deduced by the simulation of Schlumbohm's and Frommhold's experiments do not agree with any of the theoretical electron drift velocities, and suggest that the drift velocity from Frommhold's experiment coincides with an electron drift velocity represented by (W(r) + W(m))/2, while the drift velocity from Schlumbohm's experiment assumes a value close to but slightly larger than W(m).