Performance and Acceleration Process of Quasisteady Magnetoplasmadynamic Arcjets with Applied Magnetic Fields

A quasisteady magnetoplasmadynamic (MPD) arcjet with an applied magnetic Ž eld was investigated to improve the thruster performance and understand the complex acceleration mechanisms with both the self-induced and applied magnetic Ž elds. The MPD arcjet was operated with hydrogen, a mixture of nitrogen and hydrogen simulating hydrazine, and argon at discharge currents of 3 – 18 kA in high speciŽ c impulse levels around a critical discharge current predicted from the rules of Alfven’s ionization velocity or minimum input power. The application of axial magnetic Ž elds achieved higher thrust efŽ ciencies than those for only the self-induced magnetic Ž eld at constant speciŽ c impulses, and still achieved stable operations at higher speciŽ c impulses with less electrode erosion. The following guidelines were suggested to achieve higher thruster performance: 1) the axial magnetic Ž eld strength must be smaller than the azimuthal self-Ž eld strength in the main discharge region near the cathode tip, and 2) the applied magnetic Ž eld lines must expand gradually downstream for smooth expansion of plasma. Furthermore, the measured pressures on the electrodes and the current distributions in the discharge chamber showed that the overall thrust measured by a pendulum method increased, in spite of a decrease in the electromagnetic pumping thrust and a small contribution of Hall acceleration. Thus, an additional thrust component because of the axial magnetic Ž eld, such as that caused by swirl acceleration, is expected to exist.