Preliminary experiment of high-speed gas flow generation by a compact toroid injection into a gas neutralizer

A supersonic gas jet injection has been considered to be a new technique for future reactor fuelling and disruption mitigation in tokamak devices [1]. We have recently started to investigate a production of high-speed gas flow by using a compact toroid (CT) injection into a hydrogen gas neutralizer. The electron density of the CT plasma is 1$\sim $4 x10$^{21}$ m$^{-3}$, and the CT speed is 30$\sim $70 km/s in the preliminary experiment. The kinetic-energy measurements of ions and neutrals after the neutralization were carried out by using an electrostatic ion energy analyzer and time-of-flight technique. An enhancement of the H$_{\beta }$ emission level, a significant decay of the CT plasma density and the magnetic field profile have been observed after the neutralization when the neutral pressure is about 10$^{-3}$ Torr. It could be considered that high-energy neutral particles were generated by a charge exchange process from the CT plasma to the neutral particles. \newline [1] V. Rozhansky, et al., Nucl. Fusion \textbf{46}, 367 (2006).