Some Factors and Associated Mechanisms Influencing High Voltage Insulation Failure in Vacuum

An experimental program has been initiated to study dc breakdown in vacuum up to 300 kV without reliance upon preconceived conviction« of what are the mechaniami or participating factors. A range of possible factors previously reported to be influential in determining vacuum breakdown voltage was chosen with a view to studying their effects and interactions using the techniques of factorial experimental design. These methods are particularly useful in complex problems of applied physics in which many well understood fundamental physical processes operate simultaneously but with varying degrees of significance. The nature of the vacuum breakdown mechanism presents just such a problem and the relative significance or total absence of several processes may be inferred from the results. A wide selection of physical monitoring techniques has also been employed to collect supplementary data from which some basic theoretical ideas of the possible breakdown mechanism were developed These ideas have been analyzed in detail, leading to a mathematical theory of the breakdown mechanism. The theory not only explains the experimental data satisfactorily but also extends naturally into other operating regimes. Previously reported laws relating breakdown voltage and gap separation appropriate to cathode or anode dominated conditions have been confirmed and explained by the theory. New data on the influences of a weak magnetic field and of gas dissolved in the electrodes is presented and compares very satisfactory.with analytical predictions. A novel experimental technique was also developed for monitoring gas evolution instantaneously i'sing the X-rays emitted as prebreakdown current accelerates through it. The successful results of factorial experimental methods has led to the development of a unifying theory which it is hoped will form the foundation for the understanding of vacuum breakdown.