Measuring Density of a Radiatively-Cooled Reconnection Layer Using Shadowgraphy

Magnetic Reconnection on Z (MARZ) is a pulsed-power platform that drives supersonic plasma flows, generating a reconnection layer with strong radiative cooling, as relevant to a wide range of astrophysical conditions. Theory predicts that this intense radiative emission results in a colder, denser reconnection layer plasma. To diagnose this dynamic compression or "radiative collapse" in the laboratory, we field laser shadowgraphy to take snapshot images of the layer as it evolves in time. Intensity features in these shadowgram images track the layer structure and its temporally-increasing density gradients from radiative collapse. These image intensity profiles from experiment are approximately reproduced by numerically ray-tracing a simple analytical Gaussian model of the layer. Through this forward-model procedure, we thus estimate the characteristic density jump and width of the radiatively-cooled reconnection layer.