Control of Mach number of Electromagnetically accelerated plasma flow using a magnetic nozzle and its applications

本研究旨在阐明等离子体流的电磁加速机理，并利用磁喷嘴控制等离子体流的马赫数，以优化等离子体流的加速。特别地，我们直接观察到电磁力（洛伦兹力）在拉瓦尔型磁喷嘴中加速等离子体，并将其与流速测量结果进行了比较。我们详细研究了不同磁场构型下洛伦兹力的形成及其对加速度的影响。结果总结如下：1。离子的热能通过磁等离子体动力电弧喷嘴（MPDA）的拉瓦尔型磁喷嘴转化为流动能。等离子体的离子马赫数达到1以上，实现了超声速等离子体流动。等离子体的流速、离子温度和马赫数等参数的空间分布与一维等熵流动模型的理论结果一致。实验表明，等离子体流中的磁场因抗磁效应而变弱，在MPDA附近自发形成会聚磁场。由方位角电流和向内磁场产生的洛伦兹力使等离子体中的离子减速。加入强发散磁场改善了磁场的变形，将减速力转变为加速力，使等离子体流速大幅提高。结果表明，作用在等离子体流上的电磁力可以通过塑造外磁场来直接控制，并阐明了等离子体加速机理及其控制方法。

This research aims to clarify an electromagnetic acceleration mechanism of plasma flow and to control Mach number of the plasma flow using a magnetic nozzle for optimization of the plasma acceleration. Especially, we have directly observed the electromagnetic force (Lorentz force) accelerating the plasma in the Laval-type magnetic nozzle and compared it with the flow velocity measurement. We investigated in detail the formation of the Lorentz force in various magnetic field configurations and effects on the acceleration. The results are summarized as follows.1.The thermal energy of the ion was converted into the flow energy by passing through the Laval type magnetic nozzle at the muzzle of Magneto-Plasma-Dynamic arcjet (MPDA). The ion Mach number of the plasma attains to more than unity and the supersonic plasma flow was obtained.2.Spatial profiles of the several plasma parameters, flow velocity, ion temperature and Mach number of the plasma, were consistent with the theoretical results derived from the one-dimensional isentropic flow model.3.It was experimentally clarified that the magnetic field in the plasma flow became weak caused by the diamagnetic effect and the converging magnetic field was spontaneously formed near the MPDA. The Lorenz force by the azimuthal current and the inward magnetic field decelerated ions in the plasma.4.Adding a strong diverging magnetic field improved the deformation of the magnetic field and changes the deceleration force to acceleration force, which resulted in a large increase of plasma flow velocity.As a result, we have shown that the electromagnetic force acting on the plasma flow could be controlled directly by shaping the external magnetic field, and clarified the plasma acceleration mechanism and its control methods.