Vanishing of the negative anode sheath in a Hall thruster

Abstract

The transition on a Hall thruster discharge from negative to zero anode sheaths is studied with a macroscopic, stationary model. Since electron drift velocities become of the order of the thermal velocity, inertial effects on electrons must be included in the model. For thrusters with the Hall parameter still large at the anode, these effects appear only in a thin region and bound the electron azimuthal velocity at the anode to values of the order of the thermal velocity. The no-sheath regime is reached when the discharge voltage is decreased and corresponds to a small and nonmonotonic portion of the voltage-current curve. Possible connections of this behavior with experimental results are suggested. Modifications on the discharge characteristics at the regime transition are analyzed. Energy losses at the lateral walls decrease with the discharge voltage, due to the changes on the temperature profile, whereas energy losses at the anode increase only moderately. The thrust efficiency presents a maximum within the negative-sheath regime. © 2005 American Institute of Physics.