Plasma Simulations for a Miniature Ion Thruster
For most of the history of space exploration, chemical rockets have been used to put machines into orbit and to maneuver in space. While conventional rockets are able to deliver heavy payloads, they are inefficient and lack the ability to make fine movements once in space. Inductively coupled, miniature ion thrusters are an alternative that try to address the short comings of conventional rockets. While they do not launch large payloads into space, they are much more efficient while in orbit and can maneuver more precisely. In an ion thruster, plasma is generated by ionizing gas, and ions are then accelerated out of the thruster by a series of electric grids to move the thruster forward. The grid mesh size and the position of the grids relative to each other are very important to produce the most amount of useful thrust. Finding the optimal grid configuration is best found using simulation software to find the best ion trajectory as a function of grid separation. Two different simulation packages were used to find the best grid configuration for a 15 mm long, 10 mm radius thruster that uses an argon plasma. Both systems can calculate electric fields of a geometry and can determine the charged particle trajectories. OOPIC Pro is able to factor in the effects of the plasma into the trajectory calculations, but it can only perform 2D simulations. SIMION, on the other hand, can perform 3D simulations, but it does not factor in the effects of the plasma. Simulations, in which the distance between the grids was varied, were performed with the two systems. The number of ions coming out parallel to the thrust axis were calculated and compared based on the grid separation. An optimum grid spacing was determined, and these results were passed on to the fabrication team to see if the experimental data matched the simulation data. The ions expelled by the thruster were collected on metal plates with pie slice and ring shapes. These collector plate shapes allowed the azimuthal and radial distributions of the expelled ions to be estimated to determine the thruster’s performance.
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