Plasma Characteristics of Helicon Plasma Thruster using a Supersonic Gas Puffing Method*

A high-density helicon plasma is promising for a plasma source in a future electric thruster [1]. However, it has a problem of a depletion of neutral particles near the central part of a plasma [2], limiting increases of an electron density and plasma thrust. In addition, collisions between a plasma and an inner wall of a discharge tube leads to other problems of an increased plasma loss, a decrease of a fuel efficiency and higher heat load to the wall. To solve these problems, we have proposed a supersonic gas puffing (SSGP) method [3]. A concentrated neutral pulsed gas by a Laval nozzle is injected into the central part of the helicon plasma with a supersonic speed. This method is expected to overcome the depletion, to solve the problems caused by the collision and to increase an electron density and plasma thrust. We will report the distribution of neutral particles injected from Laval nozzle and the plasma characteristics using SSGP method, comparing with other gas feeding method. [1]S. Shinohara et al., IEEE Trans. Plasma Sci., 42 (2014) 1245. [2]A. Fruchtman., Plasma Sources Sci. Technol., 17 (2008) 024016. [3] A. Murakami et al., Plasma Fusion Res., 5 (2010) S1032.