| Pulsed plasma thrusters work on the principle of accelerating a plasma by a current sheet through a j&ar;xB&ar; force. Ideally, the current sheet is planar with the anode and cathode attachment points traveling at the same velocity. However, the presence of a perfectly conducting anode causes the magnetic field to penetrate faster into the plasma along the anode, leading to current sheet canting. This canting creates an off axial component of the thrust and reduces plasma acceleration.; The goal of this work was to develop an analytical model in order to describe observed current sheet canting trends. The evolution of the magnetic field within the thruster was separated into three distinct regimes, diffusion, enhanced diffusion and Hall penetration. Each of these regimes was then analyzed individually by considering certain limiting cases in the magnetic field induction equation.; Initially, the current sheet propagates through the plasma at the diffusion velocity. The presence of a perfectly conducting anode causes the electrons to travel parallel to the anode, enhancing the magnetic field diffusion in this region. The onset of the Hall modified Rayleigh Taylor instability leads to the appearance of density fluctuations within the plasma. Electrons entering these density fluctuations accelerate due to a non-potential hall electric field component, causing the magnetic field to penetrate deeper into the plasma.; The canting model is shown to be in quantitative agreement with experiments. It was shown that for low molecular weight propellants, the canting angle is a strong function of ion mass, with the anode attachment point dominated by enhanced diffusion. For high molecular weight, the anode attachment point is dominated initially by enhanced diffusion, and then by hall penetration. Based on our analysis, to mitigate canting, the theory suggests using lower atomic weight propellants and/or going to higher densities. |
