Patent ID: 7506497

Claim:
An electric propulsion device comprising: an anode and a cathode; a discharge annulus having the anode adjacent an end region thereof; at least one inlet aperture adjacent the anode, the at least one inlet aperture having propellant gas flow therethrough into the discharge annulus, the propellant gas having a first ionization potential; and an inner dielectric wall and an outer dielectric wall, wherein the inner and outer walls are concentric, wherein the discharge annulus is between the inner and outer walls, at least one of the first and second dielectric walls having pores therein, the pores having cooling gas flow therethrough into the discharge annulus and substantially adjacent the at least one of the first and second dielectric walls, the cooling gas having a first ionization potential higher than the first ionization potential of the propellant gas, the cooling gas adapted to substantially prevent at least one of secondary electron emission and sputtering of the dielectric walls.