Electron Cyclotron Resonance (ECR) magnetic nozzle thrusters typically use microwave power at a single frequency to efficiently transfer energy into a plasma via ECR heating. The use of microwave power distributed over multiple different frequencies has been rarely investigated in literature, and, in the only available previous study, the frequency difference was never less than 50 MHz.

Our study uses dual microwave signals to determine their effect on thruster performance. The frequency difference between the two signals has been found to have a significant effect on both thrust and thruster floating potential. Notably, this dependence is strongest at frequency differences less than 100 kHz. At thruster powers of 64 W and above, the use of dual microwave signals is found to increase thrust by up to 13 %. Thrust is found to peak when the frequency difference between the two signals is between 30 kHz and 60 kHz. This suggests that the performance increase may be the result of an interaction between the intermodulation-generated signal and the azimuthal magnetosonic wave.