In-beam dielectric properties of alumina at low frequencies

Loss tangent data for three commercial alumina grades measured in the range 0.1–300 kHz together with the effect of radiation are presented. Very different dielectric behaviour has been found for the three grades irradiated at 150°C and 250°C with 1.8 MeV electrons at dose rates of up to 3.5 kGy/s. In the case of Ceraten C9999, an extremely pure alumina, the increase in the loss tangent with dose rate and its dependence on frequency is due to the dc radiation induced conductivity (RIC). For Wesgo AL995 and Morgan Matroc Vitox 999 the behaviour is more complex. The influence of an applied electric field has also been examined. The importance of material selection is noted, as is the dose-dependent degradation for Wesgo AL995.