Ionisation current and ionisation coefficients at large values of E/p in hydrogen.

Abstract

Pre-breakdown ionisation current measured by Steady State Townsend experiment in hydrogen for values of E/p0 up to 1000 Vcm^-1 Torr^-1 is analysed by applying the Townsend equation, the Lucas equation and the current growth equation considering ionisation collision between positive ions and hydrogen gas molecules as well as that between electrons and the molecules.
It is seen that the degree of fit of the measured current by applying the Lucas equation is the best of the analysis by the three equations at large E/p0 values, then it is found that the ionisation current at large E/p0 values in hydrogen is affected by the gap length dependency of geometry factor, namely, loss of photons out of the gap, for the secondary process by photons.
The value of the first ionisation coefficient obtained by the analysis applying the Lucas equation increases with an increase in E/p0 for values of E/p0 _??_ 350 Vcm^-1Torr^-1, then decreases gradually when E/p0 increases. The value of the secondary ionisation coefficient γ₂ for ions obtained by the analysis applying the Lucas equation agrees with that previously reported by the authors (Technical Papers of Electrical discharge Committee IEE, Japan ED-93-90, 1993). And the value of secondary ionisation coefficient γ_p, for photons obtained by the analysis is less than one tenth of γ_i for values of E/p0 up to 500 Vcm^-1Torr^-1, then it increases rapidly when E/p0 increases and almost equals γ_i at values of E/p0 _??_ 800 Vcm^-1Torr^-1.