Radiation-induced changes in the dielectric properties of insulating ceramics at ICRH frequencies

The dielectric loss tangent of MgAl2O4, AlON, Si3N4 and various purities of alumina has been measured at frequencies between 10 and 1000 MHz before and after irradiation by 32 MeV protons generating up to 5x10-2 displacements per atom. Substantial increases of tan δ, progressive with dose, were evident in all the materials. The worst degradations, exceeding two orders of magnitude, developed at low frequencies in materials that initially had the lowest loss. These radiation induced enhancements recovered during post irradiation ageing at ambient temperatures though the smaller enhancement, manifest above 200 MHz, remained intact. The loss enhancements are consistent with Debye relaxations of radiation induced charge lattice point defects. (orig.)