DEVELOPMENT OF A 2-STAGE PNEUMATIC REPEATING PELLET INJECTOR FOR THE REFUELING OF LONG-PULSE MAGNETIC CONFINEMENT FUSION DEVICES

Next-step fusion devices, like the International Ther monuclear Experi mental Reactor (ITER), and future fusion power plants will require a f lexible plasma fueling system, including both gas puffing and high-and low-speed pellet injection. To sustain core plasma density, relativel y large pellets penetrating beyond the separatrix will have to be prov ided at a repetition rate of similar to 1 Hz for very long pulse opera tion. In the context of a cooperative agreement between the U.S. Depar tment of Energy and the Euratom-ENEA Association, Oak Ridge National L aboratory (ORNL) has collaborated with ENEA Frascati to demonstrate th e feasibility of a high-speed (2 to 3 km/s) repeating (similar to 1-Hz ) pneumatic pellet injector for long-pulse operation. A test facility was assembled at ORNL that combined a Frascati repeating two-stage lig ht-gas gun and an existing ORNL deuterium extruder equipped with a pel let chambering mechanism/gun barrel assembly. It was operated in the c ourse of three joint experimental campaigns between September 1993 and May 1995. The results of the first two campaigns appear in an earlier paper: Here, the results are reported of the third campaign, during w hich the original objectives of the collaboration were met. Both perfo rmance and reliability of the system were improved, with the facility' s being capable of delivering sequences of 2.7-mm deuterium pellets at a repetition rate of I Hz and velocities up to 2.5 km/s. The test fac ility was also briefly operated with neon pellets to explore the poten tial to produce fast ''killer'' pellets. Speeds of 1.7 km/s were easil y achieved using a piston mass of 43 g. Higher speeds should be achiev able with a system specifically designed for neon or other high-Z gase s.