Operational experience with the DIII-D neutral beam 12 cm x 48 cm common long pulse source

All four neutral beamline of the DIII-D tokamak have been converted to long pulse source operation. These common long pulse sources (CLPS) were designed for full power operation at 80 κV, 80 A, 5 sec with hydrogen. The CLPS plasma generator is equipped with cusp magnets and operates in the emission limited regime. The accelerator has an actively cooled tetrode geometry with a 10 m focus in one direction. Each new CLPS requires conditioning of the arc chamber prior to any attempt at beam extraction. It was found that the filament temperature plays an important role in the performance of the arc chamber, and that the arc operated more smoothly with the arc power supply in an unregulated mode and the filament supply in a constant voltage mode. To avoid the collapse of the voltage between the plasma and gradient grids at initial beam formation, a capacitive compensation network between the grids was added. Initial beam extraction typically started at 40 κV and progressed quickly to the full 80 κV capability with little to no degradation during shutdown periods