Polarity Effect of Large Current Spikes Produced by Artificial Charge Injection from Gas Phase into LDPE sheet

We measure current spikes superimposed on dc conduction currents through a LDPE sheet with charge injection from corona discharges in air or N2. The ions or electrons produced by the dc corona at the needle electrode pass through a screen mesh electrode and they are artificially injected into the LDPE. Negative corona discharges in N2 increase the mean repetition frequency of spikes. However, it decreases the mean repetition frequency of spikes in air. Positive corona discharge decreases the mean repetition frequency of spikes regardless of the gas components. These results suggest that the electron component in the injected charges acts as an important role for the spike current. Space charge distributions in the LDPE with the artificial charge injection are also measured.