Preliminary investigation on electrothermal instabilities in early phases of cylindrical foil implosions on primary test stand facility

Recent experiments on the implosions of 15-mm long and 2-$\mu m$ thick aluminum liners having a diameter of 12.8 mm have been performed on the primary test stand (PTS) facility. The stratified structures are observed as alternating dark and light transverse stripes in the laser shadowgraph images. These striations perpendicular to the current flow are formed early in the implosion, i.e., at the stage when the bulk of the material mass was almost at rest. A two-dimensional (2D) magnetohydrodynamics (MHD) code is employed to simulate the behavior of liner dynamics in the early phases. It is found that the striations may be produced by the electrothermal instability (ETI) that results from non-uniform Joule heating due to the characteristic relation between the resistivity and the temperature. In 2D simulations, the stratified structures can be seen obviously in both density and temperature contours as the liner expands rapidly. By analyzing instability spectrum, the dominant wavelengths of the perturbations are $8.33\mu m\text{-}20.0\mu m$, which agree qualitatively with the theoretical predictions. It is also interesting to show that ETI provides a significant seed to the subsequent magneto Rayleigh–Taylor (MRT) instability. (paper)