A repeating pneumatic pellet injector has been developed for plasma fueling applications. The repetitive device extends pneumatic injector operation to steady state. The active mechanism consists of an extruder and a gun assembly that are cooled by flowing liquidhyphen;helium refrigerant. The extruder provides a continuous supply of solid hydrogen to the gun assembly, where a reciprocating gun barrel forms and chambers cylindrical pellet from the extrusion; pellets are then accelerated with compressed hydrogen gas (pressures up to 125 bar) to velocities le;1.9 km/s (1.6 km/s for deuterium pellets). The gun assembly design can accommodate different pellet sizes and barrel lengths. Steadyhyphen;state rates of 2 sminus;1have been obtained with 2.1hyphen; , 3.4hyphen; , and 4.0hyphen;mmhyphen;diameter pellets. The present apparatus operates at higher firing rates in short bursts; for example, a rate of 6 sminus;1for 2 s with the larger pellets. These pellet parameters are in the range applicable for fueling large presenthyphen;day fusion devices such as the Tokamak Fusion Test Reactor (TFTR). Experimental results are presented, including effects of propellant pressure and barrel length on gun performance.
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