Study Of SLM Ion Optics For Electric Propulsion Thrusters

Ion optics,or ion engine grids,are key components of ion thrusters,a mature electric propulsion technology characterized by the electrostatic acceleration of ions extracted from a plasma source.They consist of electrically biased multi-aperture grids,typically two or three(screen,accelerator and decelerator),which are responsible for ion extraction and acceleration from the discharge chamber,and also prevent electron backstreaming.Typical improvements in ion optics came with the application of new materials and fabrication technologies,such as carbon-based materials and their associated production methods.The premise of the research conducted in this thesis is to understand how additive manufacturing techniques can be used to produce healthy ion optics and study how the features allowed by these new fabrication technologies can enhance ion thrusters'extraction systems and mitigate electric propulsion problems related to ion engine grids.A proof of concept of Ti6Al4V screen was fabricated and its optimization was conducted.It was concluded that typical dimensional accuracies for ion optics,of 20?m,can be reached and that precisions about 10?m can be achieved for energy densities close to the maximum fabrication energies for titanium.It was found that it is possible to selectively laser melt low porosity(under 10%)molybdenum components with energy density levels of 300 J mm^-3 and that the mechanical properties of selectively laser melted parts can reach 80%of the values corresponding to the same components fabricated through traditional methods.Additionally,it was found that he energy density applied during the SLM process influences the density(or porosity)and the CTE of the fabricated parts and that CTE variations with energy density are more noticeable(up to 20%around typical energy density fabrication values)than density(less than 10%around typical energy density fabrication values).SLM fabrication features can be used to additively manufacture ion optics with different thermal properties for screen and accelerator grid that result in a reduction of the grid-to-grid gap change and a reduction of aperture misalignment with respect to typical optics.Particularly,it was found that,for an outward domed 50cm ion optics set,by having an accel grid with a CTE 20%higher than that of screen grid,grid-to-grid gap change reduced 65%and aperture misalignment reduced 38%with respect to the typical case,where both ion optics have the same CTE.Short tests were conducted on the additively manufactured grids and a comparison between typical and SLM grids was established,paying attention to different aspects.The directions to advance this research were also pointed,mainly the sputtering erosion study of additively manufactured materials and the development of carbon-based SLM,as well as,the reproduction of sputtering erosion patterns through SLM,which could allow faster life tests of ion optics.