IN-SITU MEASUREMENT OF ELECTRICAL-CONDUCTIVITY OF ALUMINA UNDER ELECTRON-IRRADIATION IN A HIGH-VOLTAGE ELECTRON-MICROSCOPE

Radiation induced conductivity (RIC), thermally stimulated conductivit y (TSC) and radiation induced electrical degradation (RIED) are major concerns of insulating ceramic materials under the effects of flux, el ectric field and temperature and may lessen their performance in fusio n reactors. In situ measurements of the electrical conductivity of sin gle crystal alpha-Al2O3 (alumina) using the standard electric guarding technique has been performed under 1 MeV electron irradiation with an applied electric field of 93 kV/m at temperatures ranging from room t emperature to 723 K. Experimental results imply that electronic excita tion associated with radiation induced defects controls RIC of alpha-A l2O3 and show that TSC, especially the transient peak resulting from e xcess char es stored in defects, may affect the performance of alpha-A l2O3 in fusion reactors. A significant surface conductivity is confirm ed from a 1 MeV electron dose of 7.1 x 10(22)e/m(2)(3.3 x 10(-5) dpa) but no substantial bulk degradation is found under irradiation up to a dose of 7.1 x 10(22)e/m(2)(7.7 x 10(-5) dpa) at 723 K. In conclusion, it is emphasized that RIC and RIED of alpha-Al2O3 are not severe for insulators in the International Thermonuclear Experimental Reactor (IT ER) but TSC could limit their applications even to ITER.