Space Charge in Electron-Beam Irradiated Cross-Linked Polyethylene (XLPE): Charge Implantation and Release from the Bulk

The aim of the present work is to study the dynamics of the space charge in crosslinked polyethylene (XLPE) induced by electron beam irradiation. For this purpose three energies have been chosen so as to implant charges in a controlled way, in the volume, at different depths not too close to the electrodes. Pulsed Electro Acoustic (PEA) method was used to measure space charge in each sample, at the end of the irradiation process, in ambient conditions. The space charge measurements show the existence of two electron implantation sites after irradiation, one in the bulk at a depth depending on the irradiation energy and the other near the irradiated surface and a fixed position (25 μm). The application of the electric field shows that the charge implanted in the volume tends to be evacuated during the polarization. The charge accumulated persists during the relaxation and is stable after 1 hour. The current measurements reveal the impact of the irradiation in XLPE sample: the steady current measured on the irradiated sample is substantially higher compared to the one recorded on the non-irradiated specimens. Also a change in conduction mechanism is observed. The current recorded on XLPE irradiated weakly diverges from linearity with the electric field in the field range up to 40 kV/mm.