A COMPARISON OF INJECTION LAWS FOR THE SPACE-CHARGE EQUATIONS IN GASES AND DIELECTRICS

We consider the steady motion of space charge from an injecting electr ode to an earthed electrode in both a gas and a dielectric. Three mode ls governing the process of charge injection from the electrode into t he medium are compared and the resulting voltage-current characteristi cs calculated. In particular we examine injection laws in which the el ectric field, charge or current are specified. It is shown that if the injecting electrode is small in comparison to the underlying geometry then the resulting field distribution is almost independent of the in jection process. The stability of the three models is compared and it is shown that the field specified and charge specified models are alwa ys stable. The calculations are performed exactly for the case of a sy mmetric problem and make use of the Deutsch. approximation for a needl e-plane geometry.