No abstract

The azimuthal currents in the divergent magnetic nozzle of the electrodeless plasma thrusters are investigated using a two-dimensional axisymmetric particle-in-cell code. In this paper, the azimuthal currents are decomposed into four components-the diamagnetic drift current, the E × B drift current, the viscous-stress-induced current and the inertia-induced current. The azimuthal current and its four components are analyzed under three magnetization levels of 0.25 T, 0.75 T and 2.15 T. In the absence of inlet ion temperature, the azimuthal currents mainly consist of electron currents resulted from ∇p e , E × B drift and electron viscosity, while the azimuthal currents caused by the inertia can generally be neglected. The azimuthal ion currents considered negligible in previous studies are shown to be non-negligible in the highly-magnetized and collisionless magnetic nozzle, where the dominant mechanism for its formation is E × B drift and drift from the centrifugal force. In the upstream and midstream, the compositions and distributions of the azimuthal currents can vary at different radial positions and magnetization conditions because of the influence of the electric potential barrier and the high density conic. In the downstream, a vast range of paramagnetic currents are produced by the E × B drift due to ion inward detachment. And the paramagnetic stress-induced current begins to prevail due to the FELR effect. Superimposed with the paramagnetic part of the diamagnetic drift current under a high magnetic field, they can undermine the thrust gain coefficient of the magnetic nozzle.

The plasma parameters and power deposition on the walls in an orificed hollow cathode (HC) were investigated by employing the particle-in-cell (PIC) numerical method combined with Monte Carlo collisions. A new plasma power-deposition model based on the particle-wall interactions is presented. The distributions of plasma potential, plasma density, and power deposition from particles bombarding the wall surface were calculated in the PIC simulation, for the HC operating in the diode regime with a discharge current of 10.0 A and a gas flow rate of 3.5 sccm. The simulation results suggested that the electrons exhibited non-Maxwellian electron energy distributions in the insert region and that quasi-neutrality was violated outside the bulk plasma system. In addition, the results showed that the plasma power deposited on the emitter, on the upstream surface of the orifice plate, on the orifice inner wall, and on the downstream surface of the orifice plate was in the ratio of about 4:3:1:2. The results also indicated that charge exchange collisions can dramatically weaken power deposition from plasma ions.

In this paper, we present a flat target thrust stand which is designed to measure the thrust of a steady-state applied-field magnetoplasmadynamic thruster (AF-MPDT). In our experiments we varied target-thruster distances and target size to analyze their influence on the target thrust measurement results. The obtained thrust-distance curves increase to local maximum and then decreases with the increasing distance, which means that the plume of the AF-MPDT can still accelerate outside the thruster exit. The peak positions are related to the target sizes: larger targets can make the peak positions further from the thruster and decrease the measurement errors. To further improve the reliability of measurement results, a thermal equilibrium assumption combined with Knudsen’s cosine law is adapted to analyze the error caused by the back stream of plume particles. Under the assumption, the error caused by particle backflow is no more than 3.6% and the largest difference between the measured thrust and the theoretical thrust is 14%. Moreover, it was verified that target thrust measurement can disturb the working of the AF-MPD thruster, and the influence on the thrust measurement result is no more than 1% in our experiment.

No abstract