A Research On Magneto-Rayleigh-Taylor Instability Driven By A Rotating Magnetic Field

Using the equilibrium Z-pinch as a magnetic-confinement fusion system was pre-viously found to be difficult because of an unavoidable exchange or quasi-exchange mode instability.One way to avoid this instability is to give up a cylindrical geometry.This led to a loss of interest for many years and to transfer an increased focus on the Tokamak configuration.Recently,with the development of pulsed power technology and the emergence of the dynamic Z-pinch,the fusion field is experiencing renewed interest in the Z-pinch.In a dynamic Z-pinch system,magneto-Rayleigh-Taylor(MRT)instability is inevitable from implosion of plasma driven by magnetic pressure.While developing along with other magnetohydrodynamic modes,the MRT instability grows much faster and by undermining the pinch symmetry is the most dangerous.Thus,sup-pressing the MRT instability is critically important for any application involving the dynamic Z-pinch.We propose using a directional time-varying(rotating)driving mag-netic field to suppress MRT instability in the dynamic Z-pinch.The suppression effect of rotating driving magnetic field on MRT instability has been studied in a slab or cylin-drical liner configuration with a finite thickness respectively.In slab configuration,all modes are suppressed and the growth rate of the fastest mode is significantly lower than that of the classical case without a rotating magnetic field.In cylindrical liner configuration,the maximum e-folding number at stagnation of the dominant mode of an optimized alternate Theta-Z pinch is significantly lower than that of the standard Theta-or Z-pinch.The directional rotation of the driving magnetic field contributes to suppress the instabilities,which is independent of the finite thickness.The rotating frequency of the driving magnetic field and the thickness of liner are both having a monotonic effect on suppression.Their synergistic effect can enhance the suppression on MRT instability.The finite thickness effect appears only when the orientation of the driving magnetic field is time varying whereas it does not appear in the standard Theta-or Z-pinch.In addition,the nested Theta-Z pinch configuration also has good stability.Because the MRT instability is well suppressed,the alternate and nested Theta-Z pinch configuration have potential applications in liner inertial fusion.