Experimental and numerical validation of ion extractor grids

The experimental plasma thruster named the Helicon Injected Inertial Plasma Electrostatic Rocket (HIIPER) at the University of Illinois at Urbana-Champaign (UIUC) is currently being investigated. HIIPER features an Inertial Electrostatic Con nement (IEC) grid that is made asymmetrical by cutting out several wires to enlarge one of the openings in the spherical grid. When fed with a non-fusing gas such as argon, HIIPER operates in a mode where a very sharp plasma beam forms and exits the system through the IEC's asymmetry, thus allowing the existence of a net non-zero momentum. Such an operating mode is called "Jet-Mode". However, it was demonstrated that the exiting plasma beam is mostly dominated by electrons, as opposed to ions. Since electrons carry a very small momentum due to their light mass, an asymmetrical IEC producing an electron-dominated beam is not a viable propulsion device. In order to provide a greater thrust when the IEC is operating in the Jet-Mode, heavier particles such as neutralized ions must exit through the beam. This thesis focuses on the validation of so-called extractor grids, which are electrostatic components that can alter the potential pro le inside the system, and therefore enable the escape of heavier particles towards the preferred exit direction that would otherwise be trapped inside the system. The validation process mentioned before was two-fold: rst, a 2D, axisymmetric, electrostatic Particle-In-Cell code was developed in order to benchmark the di erent extractor grid designs and select those which performed the best at ion extraction. In particular, it was demonstrated that some speci c parameters have a favorable e ect on particle extraction. Second, an experimental campaign consisting in the testing of the extractor grids designs, as well as improving the experimental set-up, was carried out. Conclusions were then drawn on the capacity of HIIPER to act as a space thruster, once augmented with extractor grids. Based on the result of this work, suggestions for future research are made