Space charge injection and extraction in high divergent fields

The pressure wave propagation method has previously been used to obtain a direct measurement of space charge injection into an epoxy resin at high divergent electric fields. Here we report the results of a series of experiments designed to investigate the extraction dynamics of such injected charge by following the decay of the measured charge subsequent to voltage removal. The investigated injection conditions covered a range of voltages (10 kV to 30 kV) equivalent to maximum applied fields of 190 MV/m to 590 MV/m, and times of application (5 to 100 ms). A modification of Lindmayer's model has been used to relate the observed charge decay plots to the energy range of filled traps. The variation of the trap range with different injection conditions, together with the observed changes in the depth of penetration allow us to make qualitative statements about the way in which charge injection proceeds in high divergent fields.