Design of in-vessel mirror of ITER poloidal polarimeter

Abstract

Diagnostics in-vessel mirrors receive high neutron heating loads and high radiation heat loads because it directly faces the plasma. The in-vessel mirror of this study consists of three layers; tungsten mirror, copper-alloy heatsink and stainless-steel mirror mount. The copper-alloy heatsink is actively cooled by cooling-water pipe. The tungsten mirror is attached to the heatsink with contact pressure of 3.5 MPa and is cooled by thermal conduction to the heatsink. The mirror is not rigidly fixed to the heatsink but is able to slide on the surface of the heatsink because thermal stress in the dissimilar materials during baking needs to be avoided. The structural integrity was evaluated according to RCC-MRx code. The highest primary load to the mirror was the acceleration load during plasma disruption, and the highest secondary load was the baking temperature (240 °C). All design criteria specified in RCC-MRx code are satisfied. In addition, the design of the in-vessel mirrors was developed to facilitate adjustment of mirror angle with accuracy of 0.1° A prototype mirror was made to confirm the surface deformation owing to the assembly load. Surface deformation was 6.3 μm and was sufficiently small compared to the laser wavelength.