DIII-D neutral beam pole shields design including copper plate with removable molybdenum insert

The neutral beam copper pole shields currently in service at DIII-D have experienced localized melting and fatigue cracks in the grooves machined in the back of the copper plates. Higher power is now desired out of the neutral beams, requiring a pole shield upgrade to handle the elevated thermal load. The Princeton Plasma Physics Laboratory is responsible for the design and manufacturing of the pole shield upgrade. Since the heat flux on the pole shield is highly localized, the new design includes a molybdenum insert, positioned in the area of the maximum thermal loading, mounted in the copper plate, which is cooled by a single cooling channel. A ten segment design was implemented, with loose tongue and groove connections, to allow in situ assembly and maintenance. To validate the design, numerical simulations were performed using ANSYS workbench and consisted of two stages: 1. during the first stage unsteady fluid flow simulation was performed in conjunction with heat transfer analysis in the insert, copper plate, and water cooling system; 2. during the second stage, the temperature distribution was used to specify thermal strains, and perform transient structural analysis.