Experimental Verification of Plasma Focusing by Azimuthal Current in a Magnetic Nozzle
The theoretically predicted ability of an applied azimuthal current to focus the plasma in a magnetic nozzle (MN) was investigated experimentally. The azimuthal current was induced through the Hall effect by applying a radial electric field with a pair of concentric electrodes upstream of the throat of an electron-driven magnetic nozzle fed by an RF plasma source. Spatially resolved probe measurements of plasma density and plasma potential inside the plasma source and in the external plume show that the induced azimuthal current leads to significant focusing of the plasma on the center axis, and is a far more efficient way to enhance the centerline density than increasing the RF power in the source. This opens the door to the potential use of a focusing stage to increase the thrust efficiency of magnetic nozzles by decreasing beam divergence.