Effect of cooling the support structure on CICC stability of the TPX toroidal field magnet

The paper presents thermal design and analysis of toroidal field (TF) magnets for Tokamak Physics eXperiment (TPX), performed at Babcock and Wilcox. Magnet coils are wound of Nb/sub 3/Sn cable-in-conduit conductor and encased in a stainless steel support structure, which receives most of the operational heat load of the magnet. Channels cooled by supercritical helium are incorporated in the structure to intercept heat which would otherwise reach the winding and undermine CICC stability. A joint 3-D thermal-hydraulic model has been developed which includes two submodels iteratively coupled through boundary conditions. First submodel describes helium flow in CICC winding with thermal coupling between turns/pancakes, while the second determines temperature and heat flux distribution in the structure and cooling channels. Effectiveness of cooling arrangement is assessed, amount of heat intercepted by channels in the structure is determined. Specifics of temperature profiles and stability margins for inner and side double pancakes are discussed; obtained margins are compared with the allowables.