Experimental and synthetic shadowgraphy to diagnose a radiatively-cooled magnetic reconnection layer on Sandia's Z Machine*

The MARZ (Magnetic Reconnection on Z) campaign fields dual exploding aluminum wire arrays on Sandia’s Z Machine. On this platform, we diagnose magnetic reconnection in the presence of both strong radiative cooling and the plasmoid instability. Achieving this combination of plasma processes -- a unique capability among laboratory investigations -- makes MARZ especially relevant to extreme astrophysical environments.

Our collaboration simulates the entire MARZ load hardware in GORGON, a 3D resistive MHD code. We construct synthetic shadowgrams by ray-tracing probe beam photons through 3D electron density meshes; ray-transfer matrix analysis includes finite aperture effects. These synthetic images predict: electron density peaking in the layer center, MHD shocks outside the layer, instabilities apparent as axial structures, and the layer growing denser in time.

On the MARZ4 shot in April 2024, we employed LIONZ (Laser Imaging On Z) for shadowgraphic imaging. We analyze the four LIONZ shadowgrams, each frame with 3-ns exposure, spanning a 36-ns window around peak x-ray emission from the layer. Features in these experimental images are qualitatively consistent with simulations. However, some differences are evident, which will help better constrain initial conditions in GORGON.