THE IMPACT OF NEUTRON-IRRADIATION ON THE PERFORMANCE OF CRYOGENICALLY COOLED WINDOWS FOR ELECTRON-CYCLOTRON RESONANCE HEATING

Monocrystalline Al2O3 (sapphire) operated at cryogenic temperatures is a promising material for gyrotron windows for electron cyclotron resonance heating of fusion plasmas. A design similiar to the gyrotron window for 1 MW/140 GHz continuous wave transmission is applied to the torus window, which in addition is exposed to neutron irradiation and tritium contamination. The calculations based on a limited set of post-irradiation data show that moderate fluence levels of 10(19) fast neutrons (f.n.)/cm2 will cause unacceptable degradation of the dielectric losses and of the thermal conductivity. Additional data at lower fluences are required to assign an appropriate position of the window.