Radial profile control of a magnetically expanding plasma and its impact on a plasma thruster

Abstract

Two radiofrequency (rf) loop antennas are wound around a source tube of an inductively coupled and magnetically expanding plasma. The magnetic field lines are convergent in the source and divergent downstream of the source tube. The rf antennas are independently powered by two rf generators, providing the change in the radial profile of the ion saturation current of a Langmuir probe. Peaks in the ion saturation currents are observed around the magnetic field lines intersecting the radial source wall at the rf antenna positions, implying the presence of the electrons created near the antennas and transported along the magnetic field lines. The results suggest that the radial profile of the magnetically expanding plasma can be controlled by superimposing the plasmas created by the two antennas. The impact of the radial profile on the thrust is preliminarily investigated by attaching only the solenoid to a pendulum thrust balance immersed in vacuum.

Effects of magnetic nozzle strength and orientation on radio-frequency plasma expansion

“…Since the ion saturation current is proportional to the plasma density n p and the square root of T e , I sat was used to qualitatively assess the profile of n p . This approach has been used in other studies to infer the spatial distribution of the plasma density [18,21,29,30,35,36]. The same probes are kept floating to measure the plasma floating potential V f .…”