The Effects of the Electrodes on an Electron Avalanche†

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Abstract
The influence of the electrodes of a uniform field discharge gap on an electron avalanche ore discussed in. this paper. The presence of both electrodes reduces the number of electron/atom collisions in their vicinity thereby increasing the mean electron energy above the equilibrium valuo (∊). There is an associated decrease in the transit time and an increase in the amplification of the electrons across the gap. The spatial variation of the drift velocity, diffusion coefficient and amplification coefficient have been calculated. It has been shown that for a tube voltage greater than lOe that the electrons are no longer influenced by the electrodes when they reach the centre of the gap, and the energy and associated parameters attain equilibrium conditions. The cathode boundary condition has been analysed in detail, and has yielded an integral expression for the loss of electron current by ‘back diffusion’ which is more general than either the Thomson (1028) or Varney (1962) equation. The electron current source is shown to consist of both pole and dipole sources, which whilst escaping from the cathode surface undergoes a change in size, mean energy and energy distribution governed by the electron reflection coefficient from the cathode surface and the initial electron energy distribution.