Magneto-Rayleigh-Taylor instability driven by a rotating magnetic field: Cylindrical liner configuration

Abstract

It was previously difficult to use the equilibrium Z-pinch as a magnetic-confinement fusion system owing to unavoidable exchange or quasi-exchange mode instability; however, the development of pulsed power technology and the dynamic Z-pinch has led to renewed interest in the Z-pinch for fusion applications. In a dynamic Z-pinch system, magneto-Rayleigh-Taylor (MRT) instability is inevitable due to implosion of the plasma driven by the magnetic pressure. MRT instability develops along with other modes of instability, but it grows much faster and is the most dangerous instability undermining pinch symmetry. We propose to use a directional time-varying (rotating) driven magnetic field to suppress MRT instability in a dynamic Z-pinch. A finite thickness cylindrical liner configuration was studied. A rotational drive magnetic field is equivalent to two magnetic field components, Theta and Z, that alternate in time, referred to as an alternant Theta-Z-pinch configuration. The maximum e-folding number at stagnation of the dominant mode of an optimized alternant Theta-Z-pinch is significantly lower than that of the standard Theta- or Z-pinch and the instability is completely stabilized at a certain thickness. Directional rotation of the magnetic field is independent of the finite thickness: these parameters cooperate and enhance the suppressing effect. The finite thickness effect appears only when the magnetic field is time-varying in orientation and there is no reflection in the standard Theta- or Z-pinch. Because MRT instability can be well suppressed in this way, the alternant Theta-Z-pinch configuration has potential applications in liner inertial fusion.