Development of Ar I and Ar II Measuring System using Laser-Induced Fluorescence Methods in High-Density Helicon Plasma^*)

A particle flow velocity measurement is important to realize a behavior of exhausted plasma in an electric thruster. Laser-induced fluorescence (LIF) method provides flow velocities of ions and neutral particles through measuring velocity distribution functions of them. In addition, LIF method has some advantages, shown as follows; 1) high-spatial resolution, 2) absolute measurement of flow velocity, 3) direction-selectivity of velocity distribution functions. We have developed Ar I and Ar II LIF measuring system to observe spatial profiles of velocity distribution functions of both neutral particles and ions in an experimental device of the helicon plasma thruster, having permanent magnets as the applied magnetic field. Flow velocity of the neutral particle in the axial direction was subsonic, and ion velocity was related with a gradient of the magnetic field.