Kazunori Takahashi

An electron-beam plasma source consisting of a hot filament is installed near the throat of the magnetic nozzle immersed in a vacuum chamber. The low plasma potential of about 5 V is formed over the region of the measurement in the weakly ionized and partially magnetized argon plasma expanding along a magnetic nozzle; an electric field is much smaller than a pressure gradient, providing a force balance between the electron pressure and the magnetic pressure. This condition leads to a negligible electron E×B drift current and nearly pure diamagnetism. Measurement of the force exerted on the magnetic nozzle is performed by attaching only the solenoid to a pendulum thrust balance, clearly demonstrating the presence of the force induced by the purely diamagnetic current, which is the major contributor to the thrust generation in the magnetic nozzle plasma thruster. This indicates that the thrust can be generated only by the electrons expanding in the magnetic nozzle.

Two-dimensional steering of a magnetic nozzle in a radio frequency plasma thruster is performed by mounting four small additional solenoids in addition to a main solenoid providing the axisymmetric magnetic nozzle. The cross-sectional profile of the ion saturation current is measured by a Langmuir probe array aligned along the radial axis, which is rotated to perform the spatial scan in the cross section of the plume. The measurements show that the horizontal, vertical, and diagonal deflections of the plume can be controlled by the electric currents supplied to the four additional solenoids. Since the deflections of the magnetic nozzle and the plume can provide the thrust vector control as demonstrated in previous studies, the present result leads a two-dimensional thrust vector control in the magnetic nozzle radio frequency plasma thruster.