Migration of Space Charge Packet in Polypropylene Injected by Electron Beam Irradiation

The researches on the behavior of accumulated space charge are of great significance for improving the electrical properties of insulating dielectrics. In this study, a charge packet was injected into the polypropylene (PP) sample at a specific depth by electron beam irradiation technique, and then slowly migrated inside the sample, driven by an applied electric field. The space charge distribution was measured in real time by space charge distribution measurement to observe its migration. The calculated mobility in this experiment is $1\sim 2$ orders of magnitude lower than that obtained by other measurement methods. The conductivity calculated by the mobility was compared with the measured results of the threeelectrode method. It illustrates that the method which measuring the current reflects the behavior of all the carriers contributing to the conductivity in the sample, while the space charge distribution measurement method only reflects the behavior of the irradiation-injected electrons. Therefore, the extracted data of the space charge distribution measurement method are always smaller than those of the current measurement method, both in terms of mobility and conductivity.