New extruder-based deuterium feed system for centrifuge pellet injection

Abstract

The pellet injection systems for the next-generation fusion devices (such as the International Thermonuclear Experimental Reactor) and future fusion reactors will have to provide deuterium-tritium fueling for much longer pulse lengths (up to ≈1000 s) than present applications (typically limited to less than several seconds). Thus, a prototype pellet feed system for centrifuge pellet injection has been developed and used in long-pulse (>100 s) tests at the Oak Ridge National Laboratory (ORNL). The new apparatus has two key components: (1) a cryogenic deuterium extruder and (2) an electromagnetic pellet punch mechanism. For maximum testing flexibility, the prototype is equipped with several other active components that allow remote adjustments, including precise positioning of the punch and the capability to index through eight different pellet lengths. The new feed system was designed to mate with an existing centrifuge accelerator facility at ORNL, and experiments in the facility were carried out to document the performance and reliability of the new feed system. With 2.3-mm-diam deuterium pellets and a catenary-shaped accelerator (≈1.2 m diam), the prototype feed system was found to be capable of placing up to ≈90% of the punched pellets in the proper time/space window for pickup and acceleration by the high-speed rotating (≈50 Hz) arbor. For these operating parameters, the pellet nominal speed was ≈430 m/s, and maximum pellet feed rates of 10 pellets/s and greater were tested. In this article the equipment is briefly described, and the experimental test results are summarized. Also, issues affecting overall pellet delivery efficiency are discussed.