Modeling Magnetic Tower Jets in the Laboratory

Abstract

The twisting of magnetic fields threading an accretion system can lead to the generation on axis of toroidal field loops. As the magnetic pressure increases, the toroidal field inflates, producing a flow. Collimation is due to a background corona, which radially confines this axially growing “magnetic tower”. We investigate the possibility of studying in the laboratory the dynamics, confinement and stability of magnetic tower jets. We present two-dimensional resistive magnetohydrodynamic simulations of radial arrays, which consist of two concentric electrodes connected radially by thin metallic wires. In the laboratory, a radial wire array is driven by a 1 MA current which produces a hot, low density background plasma. During the current discharge a low plasma beta (β < 1), magnetic cavity develops in the background plasma (β is the ratio of thermal to magnetic pressure). This laboratory magnetic tower is driven by the magnetic pressure of the toroidal field and it is surrounded by a shock envelope. On axis, a high density column is produced by the pinch effect. The background plasma has ≳1, and in the radial direction the magnetic tower is confined mostly by the thermal pressure. In contrast, in the axial direction the pressure rapidly decays and an elongated, well collimated magnetic-jet develops. This is later disrupted by the development of m = 0 instabilities arising in the axial column.