Origin of Helical Instabilities in Axially Premagnetized Thin-Foil Liner Z-pinch Implosions using Hall Magnetohydrodynamics *

Helical magneto-Rayleigh-Taylor instability (MRTI) structures have been observed in z-pinch-driven liner implosion experiments with a pre-imposed axial magnetic field. We show that the formation of these helical structures can be described by a Hall magnetohydrodynamical (HMHD) model. We used the 3D extended magnetohydrodynamics simulation code PERSEUS (which includes Hall physics) [C. E. Seyler and M. R. Martin, Phys. Plasmas 18, 012703 (2011)] to study these helical instabilities and show that a Hall Instability in the low-density coronal plasma immediately surrounding the dense liner is responsible for producing helically bunched plasma striations and an associated magnetic field and current density. This seeds the helical pitch angle of the MRTI even when other proposed helical seeding mechanisms are either not present in the experiments or not accounted for in the simulations. For example, this mechanism does not require low-density power-feed plasmas to be swept in from large radius or the development of electrothermal instabilities. The Hall Instability is thus a new, independent explanation for the origin of the helical instabilities observed in axially premagnetized liner experiments. Simulation results supporting this mechanism are presented.