Analysis of DIII-D upgraded neutral beamline bending magnet thermal shields
The ion bending magnets in the DIII-D neutral beamlines are protected by 12.7 mm thick copper thermal shields. These shields are inertially cooled by single pass water lines. After years of operations, these shields have suffered from thermal cracking, which once initiated, can propagate through a water cooling line causing water leaks into the beamline. The cracks in the thermal shields are always in the same area. Recent modeling of the beam ion distribution across the thermal shields shows very uneven heating. This modeling shows peak heat fluxes (on the order of 6 MW/m2) and very high stresses near the crack locations.