Conduction and breakdown in high vacuum

In September of 1970 the 4th International Symposium on Discharge and Electrical Insulation in Vacuum was held at Waterloo University in Ontario, Canada. While the meeting was somewhat less well attended than previous ones in the series this was not reflected in the many interesting papers which were presented. The listing and discussion of these make up a large part of the material presented in this chapter. Other conferences of importance occurred in London, Munich, and Chicago. The review papers presented at Waterloo involved a wide range of topics (1–6), as can be seen from the titles. Among the important points raised by reviewers was the fact that it has now become very clear that the interpretation of prebreakdown currents using the Fowler-Nordheim (F.N.) equation can be very misleading. This is because of the likely multiplicity of emission sites coupled with the variety of adsorbate states possible on each emitter. The general effect is to lead to a lack of information concerning the emitting area. In order to explain the later stages of the field emission induced breakdown due to the explosion of a cathode emitter it has now been found necessary to consider the emission of electrons from the cathode due to the field generated by the presence of a plasma cloud (explosion created) above the surface; this enhanced emission causes intense anode heating and vapor production. The latter theory is one of many different voltage collapse processes now under review, and is as yet one of the few to have been subjected to as careful an experimental test as has the hypothesis of Davies and Biondi (3, 28, 29). The process proposed by these authors involves the detachment of a high temperature anode region and its subsequent heating in the electron beam as it crosses the gap.