Particle deposition and optical response of ITER motional Stark effect diagnostic first mirrors

Particle deposition and erosion can affect mirrors used in plasma diagnostics and this is a major concern for future fusion reactors. This subject is analysed for the first and second mirrors of the proposed motional Stark effect edge plasma current diagnostic for ITER. Particle fluxes to the diagnostic module aperture are given by edge plasma/impurity-transport solutions for convective plasma flow for full-power fusion conditions. The MC-Mirror code with input of TRIM-SP results is used to compute in-module direct, reflected and sputtered particle transport. Particles analysed are D–T and He atoms/ions from the plasma, and Fe, Be and W from first wall sputtering and/or in-module sputtering. Many of the results are encouraging for optical diagnostic use in ITER and possibly for post-ITER high duty-factor reactors. The LLNL-4B module design analysed works well in minimizing particle flux to the mirrors, with a factor of ~200–400 reduction in aperture-to-first-mirror flux. Sputtering erosion/degradation of Mo or Rh coated mirrors by incident D, T and He is negligible. IMD optical effects code analysis shows probably tolerable changes in light reflection and polarization due to mirror beryllium deposition. Tungsten flux to the mirrors is very low. Based on available but limited data, however, there is major concern about the effect of the predicted helium flux on mirror optical properties.