Bifurcation of current within gas puff Z-pinches

Summary form only given. We have found numerical evidence that large amplitude waves resulting from the Rayleigh-Taylor instability in gas puff Z-pinches may grow until individual magnetic field structures form, creating separatices between them. In the computational model used the plasma was described by collisional MHD equations (single fluid and temperature) in axisymmetric geometry. The magnetic field perpendicular to the plane of symmetry was the only component included; thermal fluxes and the thermal force terms of Braginskii were omitted. Radiative losses of the argon plasma are taken into account. We follow the development of the unstable excitations of an imploding shell or of an imploding double shell until current circulation patterns form about their respective islands. This topological change has a direct impact on the Z-pinch dynamics. The effective impedance of the plasma load changes as a result of the multiple circuits and the magnetic field develops local extrema that modify the compression. Particularly interesting changes occur when the magnetic field punches through the imploding plasma to permit connection of one loop along the axis. Under such conditions the development of a local maximum may impede or even prohibit the arrival of significant fractions of the plasma on axis. We illustrate the behavior with examples based on 300 ns argon pinch implosions to show that a current loop may form that bypasses much of the plasma, resulting in a low mass participation in the X-ray emission.