Recent performance improvement of a magnetic nozzle rf plasma thruster*

  A magnetic nozzle rf plasma thruster is an electrodeless system for space propulsion, while the thruster efficiency is relatively low compared with other mature electric propulsion devices. The high density plasma produced in the source is transported along the magnetic field lines toward the source exit, is expanded along the magnetic nozzle, where spontaneous acceleration and momentum conversion processes occur. 

 A simple thruster model have shown that the imparted thrust and the thruster efficiency can be enhanced by increasing the magnetic field strength and by enlarging the diameter of the source tube. Furthermore, the experiments have shown that the neutral injector also affects the density profile and the imparted thrust.

 Here two different rf antennas exciting m = 0 and +1 modes are tested in about 10-cm-diameter rf plasma thruster. A better rf power coupling is obtained fom m=+1 mode case, which would be in helicon mode, while the larger thrust can be obtained for m=0 mode antenna. The difference between these two cases will be discussed in the presentation. Furthermore, the larger thrust can be obtained by injecting the neutral argon gas near the thruster exit; the thruster efficiency approaching twenty percent is successfully obtained for the rf power above a few kW, the propellant flow rate of 2 mg/s,  and the peak magnetic field strength. of about several hundreds of Gauss.