The dielectric breakdown of low density gases. II. Experiments on mercury vapour

It was shown in the first paper of this series that a pre-breakdown current growth equation could be developed for low pressure gases using modern computer techniques, but that a theory of breakdown presented there could not be proved conclusively because of a lack of experimental data. This paper reviews previous related experimental work on the dielectric properties of mercury vapour and describes the development of the experimental techniques necessary to obtain this data. Results of pre-breakdown current measurements are given at (E/N) values, an order of magnitude higher than previously reported. These allow the computation of electron multiplication by electron collision in a gap as well as secondary emission coefficients by positive ion bombardment of the cathode. It is shown that the experimental results for mercury vapour confirm the theory developed in the first paper.