Pellet injector development at ORNL

Oak Ridge National Laboratory (ORNL) has been developing pellet injection systems for plasma fueling experiments on magnetic fusion confinement devices for about 20 years. Recently, the development has focused on meeting the complex fueling needs of the International Thermonuclear Experimental Reactor (ITER) and future reactors. The proposed ITER fueling system will use a combination of deuterium- tritium (D-T) gas puffing and pellet injection to achieve and maintain ignited plasmas. The pellet injection system will have to provide D-T fueling for much longer pulse lengths (up to ∼1000 s) than present day applications (typically limited to less than several seconds). In this paper, we describe the ongoing pellet injector development activities at ORNL, including the following three in direct support of ITER: (1) an improved pellet feed system for the centrifuge injector, (2) a steady-state extruder feed system, and (3) tritium extruder technology. In addition to the major activities, a repeating two-stage light gas gun for high-speed pellet injection (∼2.5 km/s) has been developed in a collaboration with ENEA Frascati; also, the production of impurity pellets (Ne, Ar, and Kr) has been demonstrated using the DIII-D and Tokamak Fusion Test Reactor pneumatic pellet injection system