PIC simulation of plasma sources for the on-ground reproduction of orbital flows

Ground testing of satellite aerodynamics in Very Low Earth Orbit (VLEO) requires facilities able to produce a rarefied flow of particles at hypersonic speeds up to 8 km/s. A plasma source can produce the required flow by electrostatic acceleration of ions. Electric thrusters for space propulsion can be repurposed for this application. We use Particle-in-Cell (PIC) to simulate these devices and the plasma plume they produce. Traditional explicit PIC schemes need to resolve the smallest electron length- and time scales, or numerical instabilities will appear. This requirement can make simulation of the device extremely expensive, unless an appropriate scaling can be applied. Recently, a new class of semi-implicit methods have been devised, mostly for applications in astrophysics. These feature exact total energy conservation, and are stable for cell sizes and time steps well in excess of the Debye length and plasma period, allowing the simulation of dense plasma in large domains. We investigate the applicability of such schemes to the simulation of the plasma plume of an Hall effect thruster. We discuss the advantages and disadvantages of adopting a semi-implicit scheme, and evaluate the accuracy of the results, also by comparing them with quasineutral plasma fluid solutions.