Simulation of the Kelvin-Helmholtz instability in the magnetized slab jet

Abstract

Two-dimensional magnetohydrodynamic simulations are performed to study the evolution of the Kelvin-Helmholtz instability for a slab jet moving parallel to the magnetic field. Surface waves are excited at each of the side boundaries, and the time evolution of the individual mode, as well as its interaction with the mode excited at the opposite boundary, is observed. The instability is very disruptive when the excited perturbations on the two side boundaries are antisymmetric. The long-term evolution of the antisymmetric perturbation shows a kinklike magnetic field structure after multiple reconnection events, while the symmetric perturbation yields wavy signatures only around the jet boundaries. Three different cases of the thin slab jet are considered with the antisymmetric perturbation: a hydrodynamic jet, a jet embedded in a uniform magnetic field, and a thermally confined magnetized jet. Although the imposed magnetic fields are weak, they show quite different evolutions. In the hydrodynamic case, the density and how patterns associated with the vortices survive until the end of the simulation without significant changes after the initial development of the instability. For the jet embedded in a uniform magnetic field, the density pattern associated with the vortex is destroyed as magnetic reconnection develops, and a steady increase in density from the central jet region toward the side boundaries is seen at the final stage when the magnetic field becomes hat again. The density and flow structures in the thermally confined magnetized jet are similar to those of the hydrodynamic case, but they change slowly with the evolution of the magnetic field. Also, it is seen that the magnetic fields that originally reside in the jet are expelled out to the side boundaries. Similar results are obtained for both the transonic jet and the supersonic jet, but the density variation is more significant in the supersonic case.