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

Abstract

Enhancing the confinement of primary electrons within the discharge chamber of an ion engine improves the eciency with which ions are produced. Consequently, this improves the ion engine’s performance. The confinement of electrons can be achieved by the application of a static magnetic field. A properly designed magnetic field makes it more dicult for electrons to be absorbed by the anode biased chamber walls. Understanding how to increase the confinement of primary electrons in the discharge chamber by altering the shape of the magnetic field is the objective of this work. The type of magnet circuit considered in this work is that composed of samarium cobalt, ring magnets. From this computational study guidelines are deduced that provide information on the proper spacing of these magnets for maximum primary electron confinement in an axisymmetric discharge chamber constructed of walls that do not interact with the magnetic field. To keep the guidelines as general as possible, ring cusp pairs are studied. The guidelines obtained for these ring cusp pairs can be applied to more complex ring-cusp configurations. Three types of ring-cusp pair arrangements are studied. The first arrangement studied is a front-back wall pair of magnetic rings which face one another, the second configuration studied is a front-side wall pair of magnetic rings at varying angles to one another, and the third configuration investigated is a side-back wall pair of magnet rings at 90 to one another. A fourth study looks at the eect of the radial oset for both the front-back wall and the front-side wall pairings. For these configurations, guidelines on the positioning and orientations of the magnet rings that provide maximum electron containment within the discharge chamber are found. To check the validity of the guidelines obtained from the pair configuration surveys, more complex ring-cusp configurations are studied. The results indicate that the guidelines obtained with the simple pair configurations are applicable to more complex magnetic circuits.