This study investigates the preliminary propulsive performances of a cathode-less plasma thruster with air as its propellant. The analysis is carried out through a global model and simulates a thruster over a power range of 0 to 50 W. The developed code considers a set of 177 chemical reactions involving 8 different species and includes empirical equations to account for electronegative effects. The analysis presents the steady-state values of species densities at 10 W, 30 W, and 50 W to gain insights into the key characteristics of plasma dynamics. Moreover, the study estimates the thrust and specific impulse and compares the results to data from models that employ xenon and iodine, aiming to understand the performances of air in low-power thrusters. Lastly, the study examines the effects of varying air inflow concentration on the chemistry, analyzing three different orbit altitudes (i.e., 200, 300, and 400 km).

An axisymmetric hybrid particle/fluid code has been applied to simulate the plasma behavior in the discharge chamber of a radio-frequency ion thruster (RIT). Suitable assumptions have been made to include the coupling with the three other elements of the thruster: the time-averaged deposited power from the radio-frequency (RF) source, the effective transparencies for ion and neutral extraction from the grid system, and the electrical connection with the external neutralizer. A detailed parametric analysis has been carried out in terms of deposited RF power and injected mass flow rate of xenon. As the RF power increases: high propellant utilization and ion beam current are obtained, the maximum plasma density moves away from the chamber center and close to the flow injector, and the beam-to-total energy efficiency decreases. As a result, for a given mass flow rate, there is an optimal RF power that maximizes the thrust efficiency. At these conditions, about 60% of the RF deposited power is lost into the walls due to the lack of magnetic confinement and multiple re-ionizations of wall-recombined neutrals penalize the inelastic losses too. Additional studies have analyzed the influence of: the electrical connections to the neutralizer, which just change the electron current paths; the effective transparency of the grids, where a large sensitivity is found to the ion transparency; the reduction of the energy accommodation of heavy species after wall impact, which penalizes much the maximum thrust efficiency; the presence of metastable atoms and stepwise ionization, which although present, have marginal effects on performances as a result of the multiple wall interactions. A global model, derived from the 2D model and constituted of algebraic expressions, can yield the main performance figures and averaged plasma magnitudes in the chamber with a relative error of up to ± 15%. Finally, 2D simulations are compared indirectly with existing data for a RIT-4.

A 2D hybrid (particle-in-cell/fluid) model has been enhanced to analyze the time-dependent coupling of the RF emission with the 2D plasma discharge in a cylindrical radiofrequency ion thruster. Electromagnetic fields are described with radial Maxwell’s equations, assuming a purely axial magnetic field induced by the external coil and plasma currents. The full time-dependent electron momentum equation is integrated. The ion response is quasi-stationary while the electron current density is highly time-dependent and develops several harmonics of the exciting frequency. Phase shifts between the electromagnetic fields and the azimuthal electron current change much with the temporal derivatives of the electron current and the inclusion of the plasma-induced magnetic field. These two features lead to a significant time-averaged cross-field magnetic confinement even in the absence of a time-averaged magnetic field, which improves the thruster performance appreciably.