Magnetohydrodynamic simulations of magneto-Rayleigh-Taylor instability mitigation and energy transport in multi-species gas-puff Z-pinches

The gas-puff Z-pinch is a well-known, efficient source of X-rays and/or neutrons, in which a cylindrical load is imploded by a pulsed-power driver due to the force arising from an applied axial current interacting with a self-generated azimuthal magnetic field. It is susceptible to the magneto-Rayleigh-Taylor instability (MRTI), which must be mitigated to achieve sufficient energy density, i.e., compression. Density tailoring, axial pre-magnetization, and increasing liner resistivity have been shown independently to be effective approaches. Here, we present 2-D radiation-MHD simulations using the HYDRA code [1] of axially-pre-magnetized multi-shell gas-puffs – one or two annular "liners" of Ne, Ar, or Kr, and a central D jet – that predict the mitigation from these approaches are additive: the axial magnetic field (Bz0) required to stabilize a Ne/D implosion is reduced from 0.7 T to 0.3 T by the addition of a second inner liner, and is further reduced by changing the outer liner to more-resistive Ar or Kr. Furthermore, the results suggest an Ne or Ar inner liner provides greater mitigation via snowplow stabilization than a Kr inner liner, as well as mitigation of ion thermal conduction losses from the fuel, the dominant loss mechanism at the 850-kA level. We conclude with a discussion on the scalability of these phenomena to 20 MA, at which level effects such as radiative cooling and fuel mixing may become more relevant.