Effects of applied magnetic fields on the performance of magnetoplasmadynamic thrusters
摘要
Since the performance of MPD thrusters is highly dependent on the applied magnetic field, we experimentally investigated the effects of magnetic field geometry. Thrust, specific impulse, and ion energy distribution were measured under various operating conditions. The results indicate that the magnetic field configuration of ring–type permanent magnets with a magnetic null point may limit effective ion acceleration, leading to reduced thrust while the permanent magnet produces a stronger applied magnetic field (BA: 0.175 T) than the electromagnet (BA: 0.016–0.065 T). This reduction could be attributed to disrupted axial electron mobility and shortened magnetic field line lengths near the magnetic null point. For the electromagnet configuration, thrust increased more significantly with discharge current at a lower argon flow rate (500 sccm) and a higher electromagnetic coil current (40 A). When the discharge current was increased to 300 A under the aforementioned conditions with an input power of 15 kW, the maximum thrust of 436 mN and the specific impulse of 2935 s were obtained. In the permanent magnet configuration, at a flow rate of 600 sccm and an input power of 10 kW, the thrust and specific impulse were 234 mN and 1340 s, respectively. In the comparable operating ranges, these values were approximately 28% and 15% lower, respectively, than those obtained with the electromagnet configuration. Besides these observations, the current-voltage (I–V) characteristics also show a dependence on the magnetic field configuration. The permanent magnet configuration exhibited a higher discharge voltage at a given discharge current, leading to reduced current levels under the same input power relative to the electromagnet configuration. The findings highlight the dominant influence of the magnetic field geometry on the thruster performance, along with the contributions of the discharge current and the argon flow rate.