A report proposes tailoring the diameters of the apertures in the accelerator grid of an ion thruster to reduce the open grid area through which un-ionized propellant gas can escape. The result would be a reduction in the loss of propellant gas and a corresponding increase in propellant efficiency. In a typical ion thruster, the plasma density decreases with radial distance from the centerline, and as a consequence, the diameters of ion beamlets decrease with increasing radial distance. According to the proposal, the apertures, through which the ion beamlets must pass, would be sized to match the diameters (with margin) of the beamlets. The decrease of the aperture diameters with radial distance would result in a significant reduction in the open grid area: In an example based on representative design parameters, the reduction could be as much as 30 percent. In this example, the transparency to un-ionized propellant would decrease from 0.24 to 0.17 and, as a result, the propellant efficiency would increase from 0.91 to 0.96.
This work was done by John Brophy of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www. techbriefs.com/tsp under the Electronics/ Computers category.
NPO-30625
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Tailoring Ion-Thruster Grid Apertures for Greater Efficiency
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Overview
The document presents a technical report from NASA's Jet Propulsion Laboratory (JPL) detailing an innovative approach to enhancing the efficiency of ion thrusters through the tailoring of accelerator grid apertures. Authored by John Brophy, the report addresses a significant challenge in ion thruster operation, particularly at high specific impulses exceeding 6000 seconds, where the loss of un-ionized propellant through the accelerator grid's apertures is a primary efficiency loss mechanism.
The core proposal involves adjusting the diameters of the apertures in the accelerator grid to align with the radial variation of ion beamlet diameters. In a typical ion thruster, the plasma density decreases as one moves away from the centerline, resulting in a corresponding decrease in the diameter of the ion beamlets. By designing the apertures to match these varying diameters, the open area of the accelerator grid can be significantly reduced. This reduction in open area minimizes the escape of un-ionized propellant gas, thereby enhancing propellant efficiency.
The report provides quantitative insights, indicating that this tailored approach could lead to a reduction in grid transparency to un-ionized propellant from 0.24 to 0.17, which translates to an increase in propellant efficiency from 0.91 to 0.96. This improvement is achieved without increasing the double ion fraction, which is crucial for maintaining the performance of the thruster.
The document includes simulations of ion beamlets extracted through the ion accelerator system, illustrating the radial variation in beamlet diameters and the corresponding adjustments in aperture sizes. These simulations support the proposed design changes and highlight the potential for significant efficiency gains in ion thruster technology.
Overall, the report emphasizes the importance of optimizing the accelerator grid design to enhance the performance of ion thrusters, which are vital for various space missions. By reducing propellant loss and improving efficiency, this research could lead to more effective and sustainable propulsion systems for future space exploration endeavors. The findings underscore the innovative work being done at JPL and its implications for advancing aerospace technology.
