Increasing the effective voltage in applied-field MPD thrusters

Increasing the effective voltage is proposed to improve applied-field magnetoplasmadynamic thrusters (AF-MPDTs) efficiency. An analytical model for both effective voltage and thrust is presented and discussed on the basis of the generalized Ohm's law. According to such a model, the effective voltage contributes to plasma acceleration and measures can be taken to affect it, including adjusting the fraction of cathode gas injection, applied magnetic field strength and discharge current. In order to verify the model, experiments were conducted on the conditions of stable operation of a 10 kW AF-MPDT. The results showed that discharge current affected thruster efficiency mainly by enhancing the back electromotive effect in plasma acceleration processes. The thrust efficiency was enhanced by an average of 9.1% by raising discharge current from 90 A to 180 A. The fraction of cathode gas injection mainly affected the resistive and Hall effect, and the thrust efficiency was enhanced by an average of 7.3% by increasing the fraction of cathode gas injection from 0.1 to 0.9. The applied magnetic field influenced the thruster performance by enhancing both the resistive and Hall effect and the back electromotive effect. The thrust efficiency was increased by an average of 3.0% by raising the applied magnetic field strength from 0.05 T to 0.17 T. It was found that the plasma acceleration of AF-MPDT was dominated by effective voltage, and increasing the effective voltage was an effective and comprehensive way to improve thruster performance.