| The Hall thruster is a mature electric propulsion device that holds considerable promise in terms of the propellant saving potential. The annular design of the conventional Hall thruster, however, does not naturally scale to low power. The efficiency tends to be lower, and the lifetime issues are more aggravated. Cylindrical geometry Hall thrusters have lower surface-to-volume ratio than conventional thrusters and, thus, seem to be more promising for scaling down. The cylindrical Hall thruster is fundamentally different from the conventional design in the way the electrons are confined in the discharge and the ion space charge is neutralized.; A comprehensive experimental and theoretical study of the physics of the low-pressure ExB plasma discharge in a cylindrical geometry Hall thruster was conducted, addressing the questions of electron cross-field transport, propellant ionization, plasma wall interaction, and formation of the electron distribution function. For this, a 2.6 cm miniaturized cylindrical Hall thruster (50--300 W input power) was developed, and Small Hall Thruster facility at Princeton Plasma Physics Laboratory was built to accommodate the experiment. Several probe diagnostic setups were developed and used for plasma measurements in the harsh plasma environment of the miniaturized thruster.; The detailed characterization of the plasma discharge in the 2.6 cm cylindrical thruster was carried out, including plasma plume and thrust measurements, and probe measurements of the plasma parameters inside the thruster. Several interesting phenomena were observed, such as, for example, the unusually high ionization efficiency and the enhanced electron transport across the magnetic field. The effect of the magnetic field on the thruster discharge was experimentally investigated and the thruster performance was enhanced by optimizing the magnetic configuration.; The results of the experiments were analyzed with the use of numeric codes (quasi-1D fluid and 3D kinetic Monte Carlo). The numeric simulations (1) suggest the existence of strong fluctuation-enhanced electron diffusion, (2) predict the non Maxwellian shape of the electron distribution function, and (3) show that the contribution of electron-wall interaction to the cross-field transport is likely insignificant. Through the acquired understanding of the new physics, ways for further optimization of this means for low-power space propulsion are suggested. |
