Diagnostic First Mirrors for Burning Plasma Experiments

Abstract

The lifetime of refractive components exposed to reactor grade plasmas will be very short and so all diagnostics which use UV (λ > 5nm), Visible and IR radiation (λ up to ∼100μm) have to view the plasma via a mirror. The diagnostic first mirrors (FM) must survive in extremely hostile conditions and maintain a good optical performance for the duration of reactor operation. In ITER-FEAT the FMs will receive intense UV and X-ray radiation, neutron and gamma fluxes, and particle fluxes (due to charge exchange atoms (CXA)). In addition, they will be subjected to the deposition of material eroded from the divertor and first wall. Of the different kinds of radiation and fluxes only CXA impact will result in direct surface modification of metallic FMs that can lead to degradation of optical properties. The fluxes of all radiation components to the mirror surface depend strongly on the mirror location. For example, the FMs of a wide-angle observation system (endoscope with open architecture) in ITER will be bombarded by CXA fluxes of about the same magnitude as the first wall. On the other hand, the FMs in the LIDAR system are located in a long duct (∼2 m in length) and will receive CXA fluxes ∼ 10⁻² of the first wall flux. This corresponds to about the lowest flux received by a FM in ITER.