Testing of sandwich molybdenum mirrors with radiative cooling for H-alpha and visible spectroscopy in ITER

Abstract

The full-scaled mock-ups of the first spherical (M1) and the second flat (M2) mirrors for H-alpha and visible spectroscopy (HA&VS) in ITER were repeatedly heated within the temperature range of 100–350°C in a vacuum chamber (0.2–5Pa). The mock-ups were made of single crystal molybdenum segments bonded to a polycrystalline molybdenum substrate through a Ti interlayer by a hot isostatic pressure (HIP) technique. The goal of the test was to verify the stability of the mirror shape in ITER relevant conditions. The curvature of the mirror was optically measured in-situ. As a result, no damage or remarkable bending on the mirrors was observed. The maximum relative change of the M1 curvature at 350°C was −0.23%. The maximum curvature of the M2 mirror at 350°C was 1/670m−1. After cooling down to room temperature, the shape of the mock-ups was fully restored. Numerical simulation of HA&VS optics performance shows that the observed bending of the mirrors does not exceed the tolerable limits.