Design and manufacture of DIII-D neutral beam pole shields with copper plates and molybdenum inserts

The copper pole shields for the neutral beam lines that have been in service at DIII-D have experienced localized melting and fatigue cracks on the front faces which have migrated into the cooling tube grooves machined in the back of the copper plates, leading to water leaks. A solution was required for longer beam pulse lengths and higher beam power operation planned for DIII-D which was limited by the pole shield heat handling capability. An upgraded pole shield design was developed by the Princeton Plasma Physics Laboratory to handle these elevated and extended thermal loads.