Plasma flows from dual exploding wire arrays for the MARZ campaign on Z

We characterize the plasma outflows generated by a dual inverse wire array load on the Z machine (Sandia National Laboratories). The MARZ (Magnetically Ablated Reconnection on Z*) campaign uses two identical 40 mm diameter, 40 mm tall exploding wire arrays with 150, 75 m diameter Aluminum wires, driven in parallel by a 20 MA, 300 ns rise time current pulse. 3D simulations with the two-temperature resistive MHD code Gorgon were used to design the arrays that would continuously ablate plasma from the wire surface to generate radially-diverging, supersonic (M_S > 5) and super-Alfvénic (M_A ~ 2) magnetized plasma outflows with frozen-in magnetic flux (R_M ~ 100). Anti-parallel magnetic fields advected by the outflows collide at the mid-plane to create a reconnection layer, which is used to study radiatively-cooled reconnection for the MARZ experimental campaign.

We use inductive probes, streaked visible spectroscopy (SVS), and gated optical self-emission imaging to diagnose the magnetic field, velocity, density, and temperature of the ablated plasma. Inductive probes positioned at different radii from the wires provide time- and space- resolved measurements of the magnetic field and flow velocity. The peak advected field is ~25-30 T, and the flow velocity is 100-150 km/s, consistent with simulations of the experimental setup. SVS optical spectra from 4 optical fibers positioned at different radii show well-defined Al-II and Al-III lines, which are sensitive to the electron density and temperature. These outflows collide with a 1 mm diameter glass rod, and generate a detached bow shock, the evolution of which is recorded using time-gated optical imaging. We use the opening angle of the bow shock to estimate the Mach number of the plasma flows.