Experiments on electrothermal instability as a seed for Magneto-Rayleigh-Taylor instability on accelerating, ablating foils

The electrothermal instability (ETI) arises whenever a current-carrying material has a resistivity that depends on temperature. When resistivity, η, increases with increasing temperature, ETI causes striations to form perpendicular to the direction of current. On pulsed-power-driven, ablating metallic loads, this process can cause sections of the target to ablate earlier than the bulk material, creating a macroscopic surface perturbation on the plasma-vacuum interface. Experiments are underway on the MAIZE 1-MA linear transformer driver at the University of Michigan to study surface perturbations produced by ETI as seeding for the Rayleigh-Taylor (MRT) instability on imploding liner [1] and accelerating foil plasmas [2]. Target foils are fabricated at the Lurie Nanofabrication Facility at UM by depositing ultrathin (200 to 500 nm) coatings of aluminum or titanium on 1.5 μm Chemplex Ultra-Polyester films. Foil thicknesses are chosen to maintain the same mass between shots, and the materials are chosen to provide substantially different values of dη/dt, which impacts the growth rate of the electrothermal instability. Targets are ablated and accelerated by driving a current of 500 to 600 kA on MAIZE, and the accelerated plasmas are imaged using a 12-frame laser imaging system. Images of these plasmas are compared to determine if initial plasma interface perturbations are measurably different on targets of different materials, with the same mass, but different ETI growth rates.