Computational design of a high-efficiency accelerator grid for a miniature ion thruster by full-aperture ion optics simulations

Full-aperture ion optics simulations have been conducted for the inhomogeneous plasma source of a miniature ion propulsion system (MIPS) to design a high-efficiency accelerator grid that provides high degree of the neutral confinement and absence of direct ion impingement. The designed accelerator grid has flat upstream and smoothly curved downstream surfaces with straight holes for easy low-cost manufacture. The diameter of the accelerator aperture was changed from the nominal value of 0.40 mm to 0.25 mm, which decreased neutral leakage and increased the propellant utilization efficiency from 31 to 50%. The direct impingement of ions caused by decreasing the accelerator aperture diameter was compensated by reducing the thickness of the accelerator grid while taking into account the inhomogeneous ion beam current density profile of the MIPS. An off-design performance simulation was conducted to validate the proposed grid design; the obtained results showed that the ion beam could be accelerated smoothly even during throttling the beam current between 75 and 150%. A grid wear simulation was also performed to compare the changes in the propellant utilization efficiency between the nominal and high-efficiency grids caused by erosion. It was found that the propellant utilization efficiency of the high-efficiency grid was greater than that of the nominal grid within the first 5,000 h of operation and that its lifetime exceeded 10,000 h of the accumulated operation time. By using the proposed high-efficiency accelerator grid and MIPS plasma source, the propellant utilization efficiency was increased, while the accelerator impingement current became negligible.