Fueling characteristics of supersonic gas puffing applied to large high-temperature plasmas in the Large Helical Device

Abstract

Supersonic gas puffing (SSGP), where a high-pressure gas is ejected through a fast solenoid valve equipped with a Laval nozzle, has been applied to large high-temperature plasmas and its fueling characteristics have been investigated in the Large Helical Device. The fueling efficiency of SSGP depends on the target plasma density and decreases as the density increases. This is due to the fueling mechanism of SSGP, where the fuel particles are supplied to the plasma edge region and then transported to the core region by diffusion. SSGP locally supplies a large number of particles to the edge region within a short time on the order of milliseconds. A fueling efficiency of ∼20% can be achieved by SSGP at a low initial density of ∼1.5 × 1019 m−3, which is more than twice as high as that of ordinary gas puffing at a similar density. Furthermore, this property leads to the additional effect of edge cooling to SSGP that will be beneficial for divertor heat load reduction.