'Dynamo Interrupted at Its Action': decaying magnetic fields in turbulent laser-plasmas*

Over the last ten years a series of laser-plasma experiments have proven the feasibility of investigating dynamo processes in the laboratory. Key findings of these experiments include the demonstration of bona fide dynamo action in subsonic turbulent plasmas with both low- and order-unity magnetic Prandtl numbers, amplification of magnetic fields in supersonic plasmas, and significantly modified transport of fast particles and heat by dynamo-generated fields. In this talk, I will present new results that address a previously unsolved puzzle from these experiments: how dynamo action ceases. Based on data from Thomson-scattering, X-ray imaging, and proton-radiography diagnostics, we argue that, once the plasma cools below a critical temperature, magnetic-field amplification is not sustained, and the fields that were initially generated by the dynamo subsequently decay. The implications of these results for the critical magnetic Reynolds number of dynamo action in both subsonic and supersonic turbulent laser-plasmas will be discussed.