Thermal and Hydraulic Analysis of the ITER Upper Vertical Stabilization Coil

The ITER upper vertical stabilization(VS) coil is a part of the ITER in-vessel coil(IVC) system, which has the abilities of restraining edge localized modes(ELMs) and maintaining plasma vertical stability. Preliminary structural analysis of the coil has revealed serious thermal stress problems. Due to the very restricted geometry space, it is necessary to perform detailed analysis on thermal and hydraulic characteristics to help optimal design of the coil. It will focus on the temperature distribution and energy balance, as well as some key factors, such as the coolant flow state and surface emissivity, which have influences on the coil performance. The APDL code and some hand calculations are employed in the analysis. The results show that the coolant convection can effectively take away the heat deposited in the coil. But improving the coolant flow state can hardly mitigate the peak temperature occurring at the edges of coil attachments, which are located far away from the coolant. Thermal radiation was expected to be a good method of cooling down these parts. But the reality is not so optimistic since it usually contributes little in the whole energy balance. However, the effect of thermal radiation will become remarkable when bad scenarios or accidents take place. Poor radiation performance of the coil will result in a potential safety hazard.