A two-stage pneumatic repeating pellet injector for refueling magnetically confined plasmas in long-pulse fusion experiments

An experiment to demonstrate the feasibility of a repetitive pneumatic pellet injector at 1 Hz in the velocity range of 2 to 3 km/s was carried out in a collaboration between Oak Ridge National Laboratory and ENEA Frascati, in the context of a cooperative agreement between the US Department of Energy and EURATOM-ENEA Association. The third round of this experiment was completed in May 1995. Both the operation and performance of the equipment were improved, and the original objectives of the collaboration have been met. The facility was also briefly operated with neon pellets to explore the potential for producing fast "killer" pellets for disruption amelioration applications. Speeds of 1.7 km/s were achieved using a piston mass of 43 g. Higher speeds should be achievable with a system specifically designed for neon or other higher Z gases. Finally, tests were performed with thin boron carbide coatings (2 pm) on the Ergal pistons. The test results were encouraging because piston friction was reduced as was the piston wear.