Monte Carlo simulation of the electron swarm in nitrogen under non-uniform field conditions

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Abstract
A Monte Carlo technique is used to investigate the behaviour of the electron swarm in nitrogen under the influence of highly non-uniform fields with a field gradient of 106 V cm-2. The assumed field gradient over the gap space corresponds to those produced in a needle-plane electrode system. The spatial variations of the electron energy distribution, drift velocity nu d and ionisation coefficient alpha /p are calculated and discussed by comparing the results with the equilibrium values obtained under the uniform field condition. A significant non-equilibrium characteristic of the ionisation coefficient is observed in the field region with the high field gradient. It is found, however, that the multiplication factor of the electron avalanche calculated by using the non-equilibrium value of alpha /p is almost the same as that obtained using the equilibrium value of alpha /p/. The validity of a previously proposed quasimicroscopic calculation method of the ionisation coefficient under the non-equilibrium condition is also examined using the data obtained by the simulation. The method is modified to be valid in the E/p region of 50-2000 V cm-1 Torr-1.