Effect of Magnetic Shielding on Plasma Plume of the Cylindrical Hall Thrusters

The cylindrical Hall thruster with permanent magnets produces a plasma plume with an unusual halo shape of the angular ion current distribution. The addition of the magnetic shield to the thruster magnetic circuit causes the plume shape to change to a conic type with the maximum ion current at the centerline. This is a typical plume shape for conventional annular Hall thrusters and the cylindrical Hall thrusters with electromagnet coils. Plasma potential measurements revealed that without the magnetic shield, a significant part of the acceleration region (~ 50%) is located outside the permanent magnet thruster. In this outside region, the magnetic field is strong, 100-300 Gauss. The reduction of the outside magnetic field with the magnetic shield causes the acceleration region to shift inside the thruster channel. In addition to the change of the plume shape, this process is accompanied with a significant plume narrowing. Experiments with a magnetically shielded configuration of a cylindrical Hall thruster with electromagnet coils demonstrate a complex dependence of the plume shape on the magnetic field topology.