Repeating pneumatic hydrogen pellet injector for plasma fueling

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 liquid‐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 ≤1.9 km/s (1.6 km/s for deuterium pellets). The gun assembly design can accommodate different pellet sizes and barrel lengths. Steady‐state rates of 2 s−1 have been obtained with 2.1‐ , 3.4‐ , and 4.0‐mm‐diameter pellets. The present apparatus operates at higher firing rates in short bursts; for example, a rate of 6 s−1 for 2 s with the larger pellets. These pellet parameters are in the range applicable for fueling large present‐day fusion devices such as the To...