Effect of a permanent-magnet-induced cusp field on a magnetic nozzle radio frequency plasma thruster

Abstract

A cusp magnetic field is formed upstream of a radio frequency antenna by using a permanent magnet (PM) array in a radio frequency plasma source attached to a diffusion chamber, while an expanding magnetic field configuration downstream of the source is maintained by placing a solenoid near the source tube’s exit, resembling a magnetic nozzle plasma thruster. The PM array is composed of 16 neodymium magnets and is designed to be movable axially, providing a movable axial location of the cusp field. The source is operated at a frequency of 13.56 MHz and an rf power of up to 2.6 kW in low-pressure argon. A force exerted on a target plate located downstream of the source is assessed by a pendulum target technique, showing that the force is increased if the cusp field is closer to the radio frequency antenna. The result is consistent with the previously reported result for the cusp field configuration applied by two sets of solenoids, while the present configuration can reduce the consumed electricity for the upstream solenoid.