Thrust imparted by a stepped-diameter magnetic nozzle rf plasma thruster

A stepped-diameter source tube is employed on a magnetic nozzle radiofrequency plasma thruster, where the magnetic field lines intersecting the wall near the antenna is separated from the radial wall near the thruster exit. The thruster is operated at a rf power up to 5 kW. Comparison with the results for the cylindrical source tube shows the increase in the thrust by about 15%-20% for the stepped-diameter case in spite of the lower plasma density near the nozzle entrance, resulting in the lower electron-diamagnetic-induced thrust component. These indirectly show that the axial momentum lost to the radial wall is inhibited by separating the plasma flow from the radial source wall.