Laser-induced evolution of hypocycloidal formation of vortex filaments from nonlinear Rayleigh–Taylor instability in a thin layer of molten metal

Abstract

A tiny vortex filament, the self-organization of which follows the contour of the nonlinear Rayleigh-Taylor ͑RT͒ instability was generated by the Gaussian laser pulse on a ns time scale. Vortex filament self-organization on the nonplanar target surface follows the asymmetric RT evolution consisting of the compressed half of the hypocycloide whose cusps have evolved into spikes, and of the other half whose cusps have evolved into loops. Since the loops cannot be formed, the filaments break into short sets of parallel rolls, oriented in radial direction. The asymmetric contour of the filament self-organization was reproduced by the two-dimensional multimode model that gives the analytical solution, based on the model of Ott. The asymmetry in the vortex filament self-organization is generated by the random wave number mode values, and by the specific phase relations between the modes.