Theoretical basis and experimental validation of the B.I.R.D. model

In experimental conditions characterized by high dc voltage (>100 kV) and long gap (>10-3m) in vacuum (p<10-2 Pa) the current flowing between metallic electrodes show the classical Fowler-Nordheim emission behavior, with superimposed random bursts, from a certain voltage up to the full voltage (conditioning processes), above which there is the 100% probability of the breakdown. Despite the effort made to get a solid understanding of these phenomena, satisfactory explanation hasn't been so far attained. A novel approach is here presented, based upon the hypothesis that the electrode surface is far from being metal made, but instead it is covered by a non metallic - dielectric compounds layer (oxides mainly). Basically, the process leading to the current burst is thought to be associated to electron depletion of the cathode layer, due to FN-like emission. Under certain conditions, the electric field inside the layer exceeds its dielectric strength, producing a microbreakdown and the associated burst of current. The evaluation of the FN-like current has to be set and solved on a quantum basis. In this work we simplify the problem solution using classical theory and then imposing quantum indetermination relations. The burst can develop into a full breakdown, provided the voltage is enough to start avalanche process at the anode. This model of Breakdown, Induced by Rupture of Dielectric layer (BIRD-model), far from being complete, still has the merit of theoretically unifying the various phenomena and of underlying the importance of the surface processes. The new features derived from the proposed model are discussed and are going to be experimentally tested in a specific set-up, currently under construction.