A ballistic model for the understanding of insulators behaviour during electron irradiation

One of the limiting factor to use materials as high voltage insulator is the dielectric breakdown: this phenomenon is induced by the destabilization of charges injected and trapped in the sample. To characterize this space charge, we develop a model of electrical charges displacements and trapping in a sample irradiated by an electron beam. On the one hand, we use an experimental method called ICM Induced Current Method. During the irradiation by an e-beam, the variations of the sample holder current are collected. They are very sensitive to the spreading and charging mechanisms. On the other hand, we adapt the one-dimensional self-consistent ballistic method to the case of a bulk insulator. Then the charging up of irradiated specimen is simulated. This model is a performing tool to the understanding of mechanisms that controls the behaviour of a material under continuous electron irradiation. Particularly, it underlines the major effect of the surface potential on the slowing down process of impinging electrons energy in case of negative charging (electron emission yield lower than 1). First results on polycrystalline alumina and polymers are presented and compared.