Significance of sample thickness and surface segregation on the electrical conductivity of Wesgo AL995 alumina under ITER environments

The electrical conductivity of 158, 295 and 610 μm thick Wesgo AL995 alumina was measured under 1 MeV electron irradiation with an electric field of 300 kV/m at temperatures up to 723 K. A significant increase in the conductivity with increasing the sample thickness is confirmed, but no substantial bulk degradation is found under irradiation up to a dose of 7.0×1022 e/m2 (7.97×10−5 dpa) at 723 K. However, surface breakdown is found only in 295 and 610 μm thick specimens. The non-existence of the surface breakdown in 158 μm thick specimen is thought to be due to the sinks effect of point defects at the surface. The X-ray analysis of the virgin and degraded specimens through scanning electron microscopy (SEM) reveals the segregation of impurities along the grain boundaries on the degraded surface. The segregation of impurities assists leaking of surface current along the grain boundaries.