Plasmoid formation and strong radiative cooling in a driven magnetic reconnection experiment

We present results from the first experimental study of stronglyradiatively-cooled magnetic reconnection. Two exploding aluminum wire arrays,driven simultaneously by the Z machine ($I_{max} = 20 \, \text{MA}$,$t_{\text{rise}} = 300 \, \text{ns}$), generate a radiatively-cooledreconnection layer ($S_L \approx 120$) in which the total cooling rate exceedsthe hydrodynamic transit rate ($\tau_{\text{hydro}}/\tau_{\text{cool}} > 100$).Measurements of X-ray emission from the reconnection layer using a filtereddiode ($>1$ keV) show a narrow (50 ns FWHM) burst of emission at 220 ns aftercurrent start, consistent with the formation and subsequent rapid cooling ofthe reconnection layer. Time-gated X-ray images of the reconnection layer showfast-moving (up to 50 km/s) hotspots inside the layer, consistent with thepresence of plasmoids observed in 3D resistive magnetohydrodynamic simulations.X-ray spectroscopy shows that these hotspots generate the majority of AlK-shell emission (at around 1.6 keV) prior to the onset of cooling, and exhibittemperatures of 170 eV, much greater than the temperature of the plasma inflowsand the rest of the reconnection layer.