Development of a new microwave discharge type ion engine

Abstract

Two types of new 10-cm-diameter microwave discharge ion thrusters have been fabricated. Microwave frequency adopted was 2.45 GHz for both the ion thrusters. In the first ion thruster, microwave was introduced into the discharge chamber through “slot-antenna”, while in the second ion thruster, it was launched through “multi-monopole-antenna”. In slot-antenna-type ion thruster, an overdense plasma was obtained, but the input microwave power was very high (over 140 W). At lower microwave power (under 80 W), plasma was not ignited. Generally, ion engine should attain high plasma density (in the order of 10 11 cm −3) at low input power. So, the second ion engine using “multi-monopole-antenna” should improve the performance. A number of monopole-antenne were set up in the discharge chamber. The multi-monopole-antenna launched microwaves by means of a divider. As a result, ion production cost of 267 eV/ion and propellant utilization efficiency of 52% were attained at an input power of 20 W.