AbstractsEngineering

Novel computational methods were developed and used to characterize plasma flows and improve the efficiency of electric propulsion devices. The focus of this doctoral research is on developing a grid-based direct kinetic (DK) simulation method that is an alternative to particle-based kinetic methods. The first part of this dissertation describes development of the grid-based direct kinetic method through verification and benchmarking. The test cases include a plasma-sheath with and without secondary electron emission from a plasma-immersed material as well as trapped particle bunching instability in nonlinear plasma waves. Using a hybrid kinetic-continuum method for the discharge plasma in a Hall effect thruster, the grid-based DK simulation and a standard particle-in-cell (PIC) method are compared. It was found that ionization events and hence ionization oscillations are captured without any statistical noise in the DK simulation in comparison to a particle simulation. In the second part, mode transition of the discharge oscillations in Hall effect thrusters, which are known to affect thruster performance, is investigated using the hybrid-DK method, in which the DK method is used for ions and a continuum method is used for electrons. The numerical simulations show good agreement with experimental data. In addition, a linear perturbation theory of ionization oscillations is derived. It is found that electron transport and temperature play an important role in such discharge oscillations whereas the common understanding in the community was that the heavy species are the main contributors. In addition, a two-dimensional simulation is developed to investigate the multidimensional ionization oscillation phenomena in the Hall effect thrusters. The effect of ion magnetization due to the magnetic field is included, showing a swirling effect of accelerated ions. Local ionization oscillations in the azimuthal direction are observed.