Description
We present updated results from magnetic reconnection experiments with both strong radiative cooling and the plasmoid instability [1,2]. These two plasma processes are intertwined with reconnection events across a wide range of astrophysical environments, including the interstellar medium, the solar chromosphere, and black hole accretion disks. The MARZ (Magnetic Reconnection on Z) experiments at Sandia National Laboratories investigate these key physics of astrophysically-relevant reconnection in the laboratory. The MARZ pulsed-power platform consists of two exploding aluminum wire arrays, through which a large current (20 MA, 300 ns rise time) is driven by the Z Machine, to generate a reconnection layer. In three separate MARZ experiments, the spacing between the two arrays was shifted; in changing the inflow parameters (velocity, density, field), we vary the reconnection layer formation and evolution. Using a laser imaging diagnostic, we take time-resolved measurements of the density structures in and near the layer. We gain a qualitative understanding of the features in these experimental images by comparison to synthetic shadowgrams produced from 3-D MHD simulations. These features include: a dense layer with temporally-increasing density gradients due to radiative collapse; standing MHD shocks outside the layer; and apparent nonuniformities along the axial direction consistent with instabilities. Quantitative measurements of these time-evolving density structures is challenging; our experimental shadowgraphic data exhibits large intensity variations, caustics, and noise. As-such, we have adopted a forward model approach: we fit our experimental intensity profiles to model profiles, which are quickly computed from a simple parameterized model of the layer structure. Fitting techniques, such as differential evolution and nonlinear least-squares, survey the multidimensional parameter space to find the best-estimates of the layer density jump, width, and length.
References:
[1] Datta, Rishabh et al. PRL 2024
[2] Datta, Rishabh et al. PoP 2024
Funding Acknowledgements:
This work is supported by the Department of Energy’s NNSA Stewardship Science Graduate Fellowship (SSGF) program under Cooperative Agreement DE-NA0003960. We also acknowledge funding through NSF EAGER PHY2213898. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525.