Development of Hydrogen Pellet Injectors at ORNL

Abstract

Pellet injectors that produce and accelerate frozen hydrogen isotope pellets are being developed at Oak Ridge National Laboratory (ORNL) for fueling of present and future plasma fusion devices. The development has focused primarily on two types of injectors: (1) gas guns, which utilize a pneumatic approach to accelerate pellets in a barrel with compressed helium or hydrogen propellant, and (2) centrifuge-type injectors, in which pellets are accelerated by centrifugal forces in a highspeed rotating track. In a single-pellet pneumatic injector, pellet speeds up to 1.4 km/s have been achieved. Three multipellet injection systems (ORNL four-pellet pneumatic design) are now functional, one each on the Poloidal Divertor Experiment (PDX), Alcator-C, and the Impurity Study Experiment (ISX-B). Currently, two repetitive devices (one of each injector type) are in operation to demonstrate steadystate fueling systems in the reactor-relevant parameter ranges of 1-km/s pellet velocity, variable pellet sizes up to 2 mm, and feed rates up to 10-40 pellets/s. The injector designs are described and operating characteristics discussed.