ALUMINA CERAMICS FOR HEATING-SYSTEMS

Data on the dielectric properties of several high purity (> 99.7%) com mercial alumina grades and sapphire are presented in wide frequency (1 kHz-145 GHz) and temperature (100 K-500 K) ranges. Loss tangent value s show differences over more than three orders of magnitude. For fusio n applications and in the frequency range of ICRH and LH, the loss tan gent effect is consistent with relaxation processes and it is found th at values as low as 10(-5) are available. On the other side, in the fr equency range of ECRH the loss tangent can be dominated either by rela xation processes or by the interaction with intrinsic lattice vibratio ns.