Wire array Z-pinch dynamics with axial magnetic fields

Abstract

Summary form only given. We describe recent cylindrical and radial ('cartwheel') wire array Z-pinch experiments on the MAGPIE facility (1 MA, 250 ns). The majority of each experiment is dominated by the gradual ablation of the cold, relatively dense wire cores into coronal plasma. Implosion only occurs when sections of the wire cores run out of mass - with cylindrical arrays this is simultaneous along the length of the array; whilst in radial arrays the high magnetic field adjacent to the cathode localises the start of implosion. In cylindrical arrays, the gaps in the wire cores result in a sheath of current snowploughing coronal plasma, that had been ablated from the wires, towards the axis. In radial arrays, however, the JtimesBthetas force results in plasma being projected out of the plane of the array, and the implosion progressing similar to a plasma focus. The dynamics of each type of array is diagnosed using a combination of laser probing, XUV framing and streak photography techniques. Formation of the snowplough sheath and the stability of the pinch during stagnation is examined and contrasted with the X-ray pulse. Finally we explore the action of different strength axial magnetic fields on array behaviour