Beam Plasma Characteristics of a Helicon Plasma Source Measured by a Spatially Resolved Optical Emission Spectroscope

Beam plasma directly forms the thrust of single-stage helicon plasma thrusters and its properties are the input parameters of the two-stage helicon thruster. Therefore, the spatial distribution of the beam plasma is vital for both single-stage and two-stage helicon thrusters. Using an optical emission spectroscope with a radial resolution of 5 mm, the spatial distribution of the beam plasma parameters and its variation with different input radio frequency (RF) powers (100-1000 W) and diameters of the discharge tube (20-60 mm) was investigated. Results show that the electron density decreases with both axial and radial distances, but the electron temperature remains nearly constant. The electron density increases with increasing input RF powers because of an increase of power deposition when the electron temperature remains constant. The radial profiles of electron density are flat, and the maximum electron densities located in the center line decrease with increasing diameters of the discharge tube, which is due to the decrease in the power density.