Physical characteristics of criteria governing the computation of air gap breakdown voltages for slightly divergent fields

The physical characteristics of criteria used to compute the breakdown voltage of air gap electrodes are investigated in this paper. Among the physical characteristics compared for these criteria are the breakdown voltage, the critical avalanche length and the electrode surface electric field. Three common electrode geometries are considered so that the computed breakdown voltages can be compared with experimentally measured values. The breakdown voltage for each electrode configuration is determined directly from the static electric field distribution. The field distributions are computed using a Laplace/Poisson finite-difference solver and boundary-fitted coordinates (EAGLE grid generation code). The physical characteristics which limit the accuracy of these breakdown criteria to slightly divergent fields are identified. Techniques for extending the accuracy of these criteria to highly divergent fields are expounded.