Millimeter wave characterisation of large area MPACVD diamond windows

Millimeter wave reflection measurements and dielectric loss measurements at 90-100 GHz and 145 GHz demonstrate that emerging commercial large area CVD diamond discs for high power gyrotron windows can be typically kept within acceptable margins in disc thickness and dielectric loss. A neutron irradiated disc shows for 10/sup -4/ dpa a reduction of thermal conductivity whereas a substantial degradation in mm-wave properties did not occur.