Thrust Enhancement of a Microwave Ion Thruster

Two optical fiber measurement techniques are used in this paper to reveal the physical mechanism of the enhancement of the thrust force of the μ10 electron cyclotron resonance ion thruster. The beam current of the μ10 thruster was increased in previous studies by changing the propellant injection method. In this study, to observe the difference in plasma distributions, optical fiber probes were inserted into the thruster under beam acceleration. The first measurement was laser absorption spectroscopy. By traversing the optical fiber, the number densities of Xe I 5p5(P3/202)6s[3/2]20 1 were obtained along the center axis. The second measurement was an electric-optic element probe measurement conducted to measure the intensities of the microwave electric field. Both measurements suggest that there is plasma in the waveguide in the conventional model of the thruster. This phenomenon is possibly caused by the leakage of electrons from the electron cyclotron resonance region to the waveguide. As a result, this paper concludes that the suppression of plasma in the waveguide is a very important measure to improve the performance of microwave thrusters.