Stray millimeter-wave radiation loads on ITER fused silica windows

Abstract

In ITER, the window assemblies will be subjected to the combination of loads due to stray radiation and neutron streaming. Therefore, adequate tests are needed to qualify the windows for the hostile environmental conditions. In ITER, two main systems will generate high power waves in the millimeter range: the Collective Thomson Scattering (CTS) system, with a total power of 1 MW at 60 GHz, and the Electron Cyclotron Resonant Heating (ECRH) system, with a maximum power of 20 MW at 170 GHz. In particular operating conditions, a significant power fraction can be deflected in other ports as stray radiation. High levels of stray radiation could damage diagnostic windows that are safety relevant components. The radiation absorbed by the fused silica window assemblies on ports #11 and #12 have been evaluated in detail. The possible effects of gamma and neutron flux on the dielectric permittivity and loss tangent, determining the absorption, have also been reviewed.