An alternative Hall thruster architecture, termed Wall-Less, that shifts the plasma discharge outside the cavity has recently been proposed. This unconventional design could offer benefits in terms of integration, operating envelope and lifetime, since the plasma interaction with the walls are significantly reduced. A permanent magnet 200 W prototype has been developed and tested to demonstrate the validity of this new concept. Preliminary experiments with a basic design have shown the magnetized discharge is stable when the electric field is shifted outwards. Moreover, the ion production and acceleration mechanisms are not affected in wall-less configuration. However, experiments have also revealed that moving the anode to the exit plane without any other changes leads to a large discharge current and low performances. In this contribution, we present experimental results about an optimized version of the wall-less concept. Studied have been performed with the 1.5 kW PPS-Flex Hall thruster as it offers a unique magnetic field flexibility. The anode geometry and the magnetic field topology have been modified to avoid interaction between the magnetic field lines and the anode surface. Thrust, discharge and ion currents have been measured over a broad range of xenon propellant mass flow rates and applied voltages. Outcomes indicate the current is strongly reduced and a satisfactory thrust efficiency, approaching the standard case, is achieved with an optimized wall-less configuration.
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