Over the last few years, first-principles simulations in combination with increasingly accurate shock experiments at multi-Mbar pressure have yielded important insights into how matter behaves under shock loading. Noble gases like argon are particularly interesting to study as a model system due to the closed shell electronic structure that results in a weak interatomic interaction at normal conditions followed by pronounced ionization and strong interaction under compression. Cryogenic argon is also optically transparent while shocked argon is metallic, displaying a reflective shock front, thus allowing for shock velocity measurement to very high precision. In this report, we present experimental results for shock compression of liquid cryogenic argon to several Mbar using magnetically accelerated flyers on the Z machine, first-principles simulations based on Density Functional Theory, and an analysis of tabular equations of state (EOS) for argon, including a newly developed wide-range EOS model.
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AcknowledgmentWe sincerely thank the many devoted specialists with Z-Operations who are involved in planning and executing experiments on the Z-machine. We thank the cryogenic team: Andrew Lopez, Keegan Shelton, and Jose Villalva for installing and running the cryostat. We thank Aaron Bowers, Nicole Cofer, and Jesse Lynch for assembling the cryo-targets. We thank Charlie Meyers for running the VISAR diagnostics and Devon Dalton for handling target design.4