New pellet injection schemes on DIII-D

The pellet fueling system on DIII-D has been modified for injection of deuterium pellets from two vertical ports and two inner wall locations on the magnetic high-field side (HFS) of the tokamak. The HFS pellet injection technique was first employed on ASDEX-Upgrade with significant improvements reported in both pellet penetration and fueling efficiency. The new pellet injection schemes on DIII-D required the installation of new guide tubes. These lines are ≈12.5 m in total Length and are made up of complex bends and turns (“roller coaster” like) to route pellets from the injector to the plasma, including sections inside the torus. The pellet speed at which intact pellets can survive through the curved guide tubes is limited (≈200-300 m/s for HFS injection schemes). Thus, one of the three gas guns on the injector was modified to provide pellets in a lower speed regime than the original guns (normal speed range 2500 to 1000 m/s). The guide tube installations and gun modifications are described along with the injector operating parameters, and the latest test results are highlighted