Three-dimensional modelling of the implosion phase of wire array Z pinches

Summary form only given. A 3D resistive magneto-hydrodynamic model is used to simulate a single wire in a cylindrical wire array undergoing implosion. As with 2D x-y plane calculations, the persistence of a cold dense wire core results in the injection of radial streams of plasma into the interior of the array prior to implosion. Variations in the mass per unit length along the wire means that some regions of the wire core run out of material and begin imploding towards the array axis earlier than others causing the residual wire core to break up. Rather than attempt to flow across the breaks in the wire plasma, the current flows along the first straight axial path, which is now inside the array. The process of "wire breaking" thus allows the full generator current to bypass the wire cores and be switched directly onto the outside of the radial plasmas streams. The ensuing implosion is then similar to the slug-like or snowplough-like implosion of a uniform fill pinch, in this case having significant axial modulation but little Rayleigh-Taylor instability growth. The origins and structure of the pinch emissions are therefore radically different to those predicted by 2D(r-z) MHD simulations of imploding shells. Simulations of the final stages of implosion may however still be possible using 2D(r-z) models provided appropriate initial conditions are used and examples of this are presented. Comparison of the 3D and 2D results with diagnostic images from the implosion phase of wire arrays on the MAGPIE generator at Imperial College and the SATURN and Z generators at Sandia National Laboratory are presented.