The electrical breakdown of solid dielectrics in non-uniform fields

The electrical breakdown of KBr, polyethylene and polymethylmethacryalate in non-uniform fields is considered. The observed breakdown voltage polarity effect, previously considered anomalous to current theories in which breakdown is governed by attainment of critical conditions at the cathode, is shown to be compatible to such theories if the effect of negative space charge within the dielectric is taken into account. It is proposed that the negative space charge arises through trapping of electrons, which are emitted into the dielectric at zero applied voltage owing to workfunction differences between the electrode and the dielectric.