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

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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.