Uniform gas distribution in ion accelerators with closed electron drift

A system for uniformly distributing propellant gas in a Hall-effect thruster (10) (HET) includes an anode (42, 42') and a porous material gas distributor (60, 89) (PMGD). The porous material (120) may be porous metal or porous ceramic. Propellant gas is directed from a supply to the PMGD for distribution into a gas discharge region (16) of the HET (10). The gas flows through the porous material (120) of the PMGD and out of the PMGD's exit surface (71) into the annular gas discharge region (16). The PMGD has an average pore size, pore density and thickness that are optimized to control the flow of the gas at the desired flow rate and distribution uniformity at a relatively short distance downstream from the PMGD. This feature allows HET to be short, significantly decreasing susceptibility to vibration problems encountered during vehicle launch. The PMGD can include a shield (79, 80) for preventing contaminants from traveling upstream from the gas discharge region from adhering to the porous metal. The shield may be integrated into the PMGD or be a separate shield. In addition, the shield may be perforated so as to allow gas to pass through the shield to further decrease the distance needed to achieve uniform gas distribution. Alternatively, the exit surface (71) of the porous metal may be oriented to face perpendicularly from the gas discharge path out of the HET, which significantly reduces the probability of contaminants adhering to the exit surface.