Plasma tests of diagnostic mirrors for ITER purposes

Abstract

One of the main problems of ITER optical diagnostics is the degradation of collecting mirrors by erosion or impurity deposition. It is suggested to reduce the degradation by small entrance pupil in optical system. The prototype of endoscope optical system for H-alpha ITER diagnostics is under testing in T-10 tokamak. It has entrance pupil of 1mm diameter. Three molybdenum mirrors were tested between 1 and 3 years. In spite of local degradation or surface damages appeared after 2 years of operation, the diagnostics remained functional.In parallel, the first mirror assembly (FMA) with 4mm pupil was tested in a magnetron sputtering installation. Deuterium pressure was 0.7Pa during magnetron discharge with 1A current. Estimated flux of aluminum and carbon atoms was about 1014atcm−2s−1 on the FMA entrance pupil. As a result, FMA molybdenum mirrors preserved their reflectivity after 40h of exposure which can be considered as 400 ITER pulses. Thereby small entrance pupil appears as a good solution for first mirror protection.