Spatial measurement of axial and radial momentum fluxes of a plasma expanding in a magnetic nozzle

Abstract

Spatial profiles of axial and radial momentum fluxes of a plasma expanding in a magnetic nozzle is revealed by using a momentum vector measurement instrument located downstream of a radiofrequency plasma source, where the radial and axial forces exerted to the detector plate facing the source side are independently, directly, and simultaneously obtained. It is shown that a conical structure having high electron temperature and plasma density is significantly responsible for the axial momentum flux, which corresponds to the thrust in an electric propulsion device. The radially outward momentum flux is detected at the outer region of the conical structure, where the electron pressure gradient is formed; implying that the ions are radially accelerated by an electric field. The increase in the radially integrated axial momentum flux along the axis is demonstrated, where the gain of the axial momentum flux occurs at the radially peripheral region of the plasma expanding along the magnetic nozzle.