Study On The Mechanism Of Plasma Beam Focusing In Hall Thrusters With Variable Cross-Section Channel

Hall thruster, as a kind of electrostatic propulsion device which is widely used, has reached a stage that the engineering design theory about it has been very mature. Meanwhile, little understanding of physical mechanism in the channel has become a bottleneck to further enhance its performance. Hall thrusters with variable cross-section channel have better propellant utilization when the propellant mass flow rate is small. However, the bad plume focalization deters this kind of Hall thruster from booming in engineering applications. This paper presents the study of plasma beam focusing in Hall thrusters with variable cross-section channel from the respects of propellant ionizing and corresponding magnetic field.This paper first gives the result of sudden variable cross-section channel affecting on plasma beam focusing in Hall thrusters. Combined the effect of sudden variable cross-section channel on propellant ionization and corresponding magnetic field, the paper presents the theoretical analysis on the effect of sudden variable cross-section channel on plasma beam focusing. As the study shows, the sudden variable cross-section channel enhances the propellant ionizing with the result of increased plasma density and electron temperature. At the same time, the increased magnetic field intensity enhances the level of ions being magnetized. These two factors give a bad potential profile in the channel which is not good for plasma beam focusing. Also, this point is proved through PIC (Particle-in-Cell) simulation.Also the paper gives the effect of sudden variable cross-section channel on electron near wall transport through PIC simulation. As the study shows, the variable cross-section channel increased the electron near wall transport on both sides of the protuberance and makes the two parts become two of the three main areas of electron near wall transport.What is more, the paper gives rules of propellant mass flow rate and magnetic field intensity affecting propellant ionization, potential profile and electron near wall transport in the sudden variable cross-section channel. As is stated, when the propellant mass flow rate is reduced, the ionization zone moves into the channel, coupling between ionization zone and acceleration zone is increased, and electron near wall transport in the acceleration zone is reduced relatively. When the magnetic field intensity is reduced, the ionization zone moves out forward to the exit of the channel, and the electron near wall transport in the acceleration zone is increased.Finally, this paper parametrically designs channel with morphology from natural erosion and gives experimental study on this kind of channel, which shows that Hall thrusters equipped with channels with morphology from natural erosion have the plasma beam better focused and the overall performance is better.