DESIGN OF A REPEATING PNEUMATIC PELLET INJECTOR FOR THE JOINT EUROPEAN TORUS.

A three-barrel pneumatic pellet launcher that serves as the principal component of a plasma fueling system for the Joint European Torus (JET) is described. The device consists of three independent machine-gun-like mechanisms that operate at cryogenic temperatures (14-20 K). Individual high-speed extruders provide a continuous supply of solid deuterium to each gun assembly, where a reciprocating breech-side cutting mechanism forms and chambers cylindrical pellets from the extrusion; the deuterium pellets are then accelerated in the gun barrels with controlled amounts of compressed hydrogen gas (pressures up to 100 bar) to velocities of less than equivalent to 1. 5 km/s. The injector features three nominal pellet sizes (2. 7, 4. 0, and 6. 0 mm) and has been tested at pellet repetition rates of 5, 2. 5, and 1 Hz, respectively. Each gun can operate (individually or simultaneously) at the design repetition rate for 15-s pulses (limited only by the capacity of the extruder feed system). A remote, stand-alone control and data acquisition system is used for injector operation.