Takahashi Kazunori
Department of Electrical Engineering, Tohoku University, Sendai, 980-8579, Japan.
Sci Rep. 2021 Feb 2;11(1):2768. doi: 10.1038/s41598-021-82471-2.
Development of a magnetic nozzle radiofrequency (rf) plasma thruster has been one of challenging topics in space electric propulsion technologies. The thruster typically consists of an rf plasma source and a magnetic nozzle, where the plasma produced inside the source is transported along the magnetic field and expands in the magnetic nozzle. An imparted thrust is significantly affected by the rf power coupling for the plasma production, the plasma transport, the plasma loss to the wall, and the plasma acceleration process in the magnetic nozzle. The rf power transfer efficiency and the imparted thrust are assessed for two types of rf antennas exciting azimuthal mode number of [Formula: see text] and [Formula: see text], where propellant argon gas is introduced from the upstream of the thruster source tube. The rf power transfer efficiency and the density measured at the radial center for the [Formula: see text] mode antenna are higher than those for the [Formula: see text] mode antenna, while a larger thrust is obtained for the [Formula: see text] mode antenna. Two-dimensional plume characterization suggests that the lowered performance for the [Formula: see text] mode case is due to the plasma production at the radial center, where contribution on a thrust exerted to the magnetic nozzle is weak due to the absence of the radial magnetic field. Subsequently, the configuration is modified so as to introduce the propellant gas near the thruster exit for the [Formula: see text] mode configuration and the thruster efficiency approaching twenty percent is successfully obtained, being highest to date in the kW-class magnetic nozzle rf plasma thrusters.
磁喷管射频（rf）等离子体推进器的研制一直是空间电推进技术中具有挑战性的课题之一。该推进器通常由射频等离子体源和磁喷管组成，源内部产生的等离子体沿磁场传输并在磁喷管中膨胀。施加的推力受到等离子体产生的射频功率耦合、等离子体传输、等离子体向壁面的损失以及磁喷管中等离子体加速过程的显著影响。对于激发方位模数为[公式：见原文]和[公式：见原文]的两种射频天线，评估了射频功率传输效率和施加的推力，其中推进剂氩气从推进器源管的上游引入。[公式：见原文]模天线在径向中心处测得的射频功率传输效率和密度高于[公式：见原文]模天线，而[公式：见原文]模天线获得的推力更大。二维羽流特性表明，[公式：见原文]模情况下性能降低是由于在径向中心产生等离子体，由于没有径向磁场，对施加到磁喷管的推力贡献较弱。随后，对结构进行了修改，以便在[公式：见原文]模结构的推进器出口附近引入推进剂气体，并成功获得了接近20%的推进器效率，这是迄今为止千瓦级磁喷管射频等离子体推进器中最高的。
