Acceleration of large size deuterium pellets to high speeds using a small two-stage pneumatic gun

Abstract

The technology of two-stage pneumatic pellet injectors represents by far the most reliable way to perform deep plasma fueling, with pipe gun devices capable of routinely launching small or medium size (up to 4 mm) D2 pellets at speeds in excess of 3 km/s, using rather small two-stage guns. It is still an open question, however, if scaling of the pellet size to the International Thermonuclear Experimental Reactor relevant values (6–8 mm) will or will not require a somewhat proportional increase in the physical size of the two-stage gun. In order to investigate this question, an extensive study was carried out at ENEA Frascati, using numerical simulation codes. It clearly indicated that a “compact” two-stage gun may have the potential to accelerate large size pellets at speeds up to 5 km/s. A low cost experiment was also scheduled. A spare pipe-gun cryostat of the single-shot two-stage pneumatic injector, previously used for high-speed pellet fueling of the Frascati tokamak upgrade, was modified in order to accommodate larger bore (up to 6 mm) launching barrels. In this article, we will mainly discuss the results of numerical simulations. A very early experimental campaign, carried out in 1996, will also be briefly reported, during which intact 6 mm D2 pellets were launched at speeds up to 2.5 km/s.