*2.4.3 Behavior under continuous irradiation*

Besides, when measurements are performed during irradiation on the previously irradiated samples, the dc voltage flashover varies. It decreases as the energy of radiation in increased. Starting at 26.9 kV under 5 keV electron irradiation, the dc flashover voltage is of about 10.5 kV under 30 keV electron irradiation. The dc flashover voltage was equal to the value recorded on raw PI under 17.5 keV electron irradiation. Below this energy, the electrons from the beam are repelled and the dc flashover voltage remains higher than on Virgin PI. On the other hand, when the energy is higher, the electrons can reach the surface and contribute to the flashover phenomenon and the initial dc flashover voltage is decaying. The effect of attraction of the electron of the beam toward the anode is not so important when the energy of the beam is high. The contribution of injected electron below the surface on the electric field distortion is in favor of the reduction of the dc voltage flashover decay.
