Exploring Magneto-Rayleigh-Taylor Instability Development in Solid Liner Dynamic Screw Pinches using Three-Dimensional Magnetohydrodynamic Modeling

Abstract

Magnetically enhanced hydrodynamic instabilities deleteriously effect fuel compression and confinement (and thus fusion yield) in Magnetized Liner Inertial Fusion (MagLIF). These helically oriented magneto-Rayleigh-Taylor (MRT) instabilities in MagLIF have been mitigated by use of dielectric coatings on the outer surface of the metallic liner; the coatings are thought to reduce growth of electrothermal instability (ETI) structures, hypothesized to be an important pre-implosion seed for subsequent MRT growth. Use of dynamic drive magnetic field polarization via a dynamic screw pinch is proposed to reduce cumulative MRT growth in-flight during liner acceleration, providing a novel means to improve implosion stability. This concept has been explored analytically [1] and numerically [2] with focus on establishing the physics design basis for exploration in experiments on the Z accelerator. We present results from three-dimensional high resolution magnetohydrodynamic (MHD) simulations that focus on modeling MRT development in liner implosions driven by azimuthal and axial magnetic field components; as the liner implodes, the azimuthal component (inversely proportional to the liner radius) increases and the initially-helical drive magnetic vector field polarization dynamically rotates towards the equator. Cumulative growth, wavelength, and orientation of MRT are compared for simulations with different specified drive field ratios (axial drive magnetic field component divided by azimuthal drive magnetic field component measured at the imploding liner surface). Select results are compared to the linear theory [1]. The stabilizing effects of dynamic magnetic field polarization observed in MHD simulations indicate that dynamic screw pinches deserve further experimental study as a viable mechanism for effectively improving implosion uniformity in magnetically driven liner implosions.