Development of Magnetised Plasma Rockets using Inverse Design and Kinetic Simulation

Abstract

Electric propulsion systems have become a leading solution for accelerating spacecraft, driving an appetite for lifetime, mass, and efficiency improvements. Advancements in additive manufacturing and computing power were leveraged to rapidly design the magnetic fields directly impacting an electric thruster’s performance. Fully kinetic particle-in-cell (PIC) simulation methods were also harnessed to characterise plasma sources beyond experimentation. To validate the plasma rocket models, simulations were first performed on existing and well characterised Cathodic Arc devices. The Cathodic Arc PIC models are the first to include continuously generated cathode spots and to model the far-field plasma jet. Results successfully predicted the evolution of the ion charge state energy distributions shown in experimental data and explored novel physics. To address the inverse design problem presented by the magnetic circuits of electric thrusters, the novel use of Monte Carlo sampling and conditional filtering was applied to design the magnetic nozzle of an RF plasma rocket. Following an analysis of designs with PIC simulation, devices were constructed with a helicon source, allowing plasma jet density and ion energy to be determined experimentally, with results further validating the model. A novel evolution-based design and optimisation strategy was developed to overcome the limitations of the sampling method. The objective function integrated a numerical model for plasma behaviour within a magnetic field to assess candidates across a large design space. Designs with different scores were constructed using an array of Neodymium magnets confined within an additively manufactured vessel situated about a helicon source. Experimentation showed a correlation between thrust and objective score, and an agreement with simulation data. The techniques developed in the research process can now be applied to improve the design of electric thrusters and other electromagnetic devices.