It is reported that temperature gradient can enhance hetero-charge accumulation at the low temperature end of polyethylene

while at the high temperature side only a small quantity of homo-charge accumulates. To understand this observation

we discussed the mechanism of how the temperature gradient influences hetero-charge formation based on two theories

respectively

namely the ionization of impurities in insulation and the blocked extraction of injected carriers

and found that temperature gradient across the sample thickness would influence the space charge distribution through influencing carrier mobility

and temperature difference between two electrodes through charge injection and extraction at the electrode ends. In order to verify this theory

we measured the space charge distribution in samples of different thicknesses under different temperatures. The results show that

with the same temperature difference but different temperature gradients

more hetero-charge accumulates in thin samples

however

it more accumulates in thick samples with the same temperature gradient but different temperature differences. It is concluded that both temperature gradient and the temperature difference between electrodes accelerate the hetero-charge accumulation at the lower temperature end.