Operation and reliability of a pneumatic hydrogen pellet injection system on the Joint European Torus

Developed at the Oak Ridge National Laboratory, the pneumatic-based, hydrogen-isotope, pellet injector was installed on the Joint European Torus (JET) during 1987 and has since been used in plasma fueling experiments. The injector consists of three independent machine-gun-like mechanisms (nominal pellet sizes of 2.7, 4.0, and 6.0 mm in diameter), and it features repetitive operation (1-5 Hz) for quasi-steady-state conditions (>10 s). An extensive set of injector diagnostics permits evaluation of parameters, including speed, mass, and integrity, for each pellet shot. Pellet speeds can be varied but typically range from 1.0 to 1.5 km/s. Over 5000 pellets have been fired with the equipment at JET, including about 2000 pellets shot for plasma fueling experiments. In recent experiments, the system performance has been outstanding, including excellent reproducibility in pellet speed and mass and a reliability of >98% in delivering pellets to the plasma. >