In this paper, we describe the operation of a two-stage wire array z-pinch driven by the 1.4 MA,
240 ns rise-time Magpie pulsed-power device at Imperial College London. In this setup, an inverse
wire array acts as a fast current switch, delivering a current pre-pulse into a cylindrical load wire
array, before rapidly switching the majority of the generator current into the load after a
100–150 ns dwell time. A detailed analysis of the evolution of the load array during the pre-pulse is
presented. Measurements of the load resistivity and energy deposition suggest significant bulk heating
of the array mass occurs. The 5 kA pre-pulse delivers 0.8 J of energy to the load, leaving it
in a mixed, predominantly liquid-vapour state. The main current switch occurs as the inverse array
begins to explode and plasma expands into the load region. Electrical and imaging diagnostics indicate
that the main current switch may evolve in part as a plasma flow switch, driven by the expansion
of a magnetic cavity and plasma bubble along the length of the load array. Analysis of
implosion trajectories suggests that approximately 1 MA switches into the load in 100 ns, corresponding
to a doubling of the generator dI/dt. Potential scaling of the device to higher current
machines is discussed. V