Computational Study of Ring-Cusp Magnet Configurations that Provide Maximum Electron Confinement

Enhancing the confinement of primary electrons within the plasma in a discharge chamber of an ion thruster improves plasma ionization and consequently the thruster\u27s performance. This work computationally calculates the location, position, and orientation of the permanent magnets that provide a ring-cusp magnetic field that maximizes electron confinement in an axi-symmetric cylindrical aluminum-wall discharge chamber. Small samarium cobalt magnets are circumferentially arranged in a ring around the front, side, or back wall of the chamber. The generated ring-cusp magnetic field for any specified magnet configuration is calculated using MAXWELL2D, a two dimensional electromagnetic field simulation computer code. For various magnet configurations, PRIMA, a particle-in-cell computer code modified by Mahalingam and Menart, is used to model the trajectory of the primary electrons in the magnetic field. The confinement length, the length of time an electron is retained within the chamber, is output by PRIMA, and it is the parameter used to determine the performance of the magnet configurations surveyed. The performance of various magnet ring pairs are studied and guidelines on the location, position, and orientation of the magnet rings are obtained. These guidelines are then combined to give complex ring-cusp magnet ring arrangements on a fixed size discharge chamber. For three complex arrangements having three magnet rings, a decrease in the chambers confinement ability is seen when the applied guidelines are slightly violated. This observed decrease validates the guidelines deduced in this work