Effect of applied magnetic fields on the performance and discharge characteristics of MPD thrusters

Applied-Field MPD thrusters (AF-MPDT), which have high thrust density, reasonable fuel cost, and high specific impulse, are the electromagnetic type thruster and the performance and discharge characteristics of AF-MPDT are strongly affected by the applied (external) field. In this work, the performance characteristics of a 10-kW class AF-MPDT in various magnetic field geometries were investigated. It was found that the thrust and specific impulse increased with mass flow rate and input power due to the increased ion density rather than ion energy, which was confirmed by the OES and RPA measurements. We also investigated how the thruster performance changes as the geometry and intensity of the magnetic field inside the discharge channel vary by adjusting the position of the permanent magnets. The results showed that the ratio of the radial to axial magnetic field was more correlated with the thruster performance than the strength of the magnetic field [1]. Furthermore, we compared the performance of the permanent magnet MPDT with that of the electromagnet MPDT. The results showed that the permanent magnet generates a stronger applied magnetic field (0.175 T) than the electromagnet (0.016 - 0.065 T), but the magnetic field configuration of the permanent magnet with a magnetic null point can limit the effective ion acceleration, reducing the thrust. For the electromagnet, the thrust increased more steeply with discharge current at low flow rates (500 sccm) and high electromagnetic coil currents (40 A). When the discharge current was increased to 300 A under the aforementioned conditions, the maximum thrust was 436 mN and the specific impulse was 2935 s.