Thermo-hydraulic analysis of the first mirror and its cooling system for the ITER core CXRS diagnostic

The first mirror (M1) as an important part of the CXRS diagnostic system is responsible for acquisition and transportation of the optical signal of required quality from the ITER plasma to detectors. At the same time, the M1 is the most vulnerable component of this system working in drastic and severe conditions caused by its location in the direct view of the plasma. To minimize impurities deposition and guarantee the required lifetime for M1 its temperature shall be maintained within the operational range of 350 ± 50 °C. The computation of M1 of the reference CXRS design demonstrates that, firstly, helium is the best candidate among the analyzed gases (He, N2, Ar) to be used as a coolant to maintain the M1 temperature in the required operational range of 350 ± 50 °C giving the highest heat transfer coefficient and the lowest hydraulic losses at moderate flow rates (vgas = 40–60 m/s) and, secondly, optimization of the cooling channels configuration together with an increase in the gas velocity and/or with heat transfer intensifiers makes it possible to provide the required M1 temperature conditions.