Characterization of absorber materials for high-power millimetre waves

In electron cyclotron heating systems using gyrotrons with powers up to 1MW, calorimetric loads and absorbers for stray radiation are needed. Furthermore, absorbing coatings are used inside plasma vessels of fusion experiments (e.g. W7-X). For high-power millimetre waves, absorbing coatings on copper or aluminium with optimized properties are required. In this context, measurements of the absorption coefficient of coatings from B/sub 4/C and various mixtures of Al/sub 2/O/sub 3/ and TiO/sub 2/ are presented as a function of thickness, angle of incidence and frequency, and dielectric properties are deduced unambiguously.