NSTX-U Global Thermal Analysis for Bakeout and Normal Operation Scenarios

The NSTX-U recovery project will deploy new plasma-facing components (PFCs) to meet the updated high heat flux requirements, increased heating power, and longer pulse durations compared with NSTX. Many components have been redesigned and replaced. To address the influence of high heat load, heat transfer, and distribution in the whole machine, an ANSYS two-dimensional (2-D) model was built for the global thermal analysis of NSTX-U recovery. This 2-D model includes most of the aspects of the updated design of the center stack casing first wall, new inboard divertor and cooling plate, updated outboard divertor, etc. It models the radiative surfaces of almost all the in-vessel components, vessel, insulation, and cooled coils. It models the convection heat exchange on all the out-of-vessel components and environment. Thee water cooling of coils, casing, and vessel, and helium heating and cooling of PFCs are included, too. Heat loads of normal operation are from the plasma energy deposition of five predefined typical thermal scenarios. Heat sources for bakeout are from Joule heat generation, helium gas, and hot water heating.

The results of this global model are used to predict temperature ratcheting and heat distribution of different thermal scenarios, to understand heat transfer and heat removal for bakeout, to evaluate different cooling schemes for operation and heating schemes for bakeout, and to estimate heat loads to the cooling system of the Ohmic heating and Poroidal field coils, heat loss from the system, etc. The temperature and heat flux results are also used as the base and comparison for the detailed thermal analyses of the substructures. This global model is also being converted to a structural model to evaluate thermal growth and thermal stresses. Thermal loads can be mapped to detailed three-dimensional structural models and combined with electromagnetic loads to evaluate different component designs.