Onset, Subsistence, and Decay of Magnetic Fields in Subsonic and Supersonic Turbulence*

In a series of laser-driven laboratory astrophysics experiments, carried out by the TDYNO collaboration, we have proven the feasibility of investigating dynamo processes in the laboratory. Key findings include the demonstration of bona fide dynamo action in subsonic turbulent plasmas with both low- [Tzeferacos et al. Nat. Comm. 9, 591, 2018] and order-unity [Bott et al. Proc. Natl. Acad. Sci. U.S.A. 118, e2015729118, 2021] magnetic Prandtl numbers, amplification of magnetic fields in supersonic plasmas [Bott et al. Phys. Rev. Lett. 127, 175002, 2021], and significantly modified transport of charged particles [Chen et al. Astrophys J. 892, 114, 2020] and heat [Meinecke et al. Sci. Adv. 8, eabj6799, 2022] by stochastic magnetic fields. Here we present new results from experimental campaigns at the Omega Laser Facility of the Laboratory for Laser Energetics where we (i) demonstrate the onset of dynamo action in supersonic turbulence, which persists enough to reach saturation with the available kinetic energy, and (ii) show how dynamo action ceases in subsonic turbulence, once the plasma cools below a critical temperature, and how the dynamo-amplified magnetic fields subsequently decay. We detail the experiments that led to these results, as well as the FLASH simulation campaigns that we executed for their design and interpretation. The implications of these results for the critical magnetic Reynolds number of dynamo action in both subsonic and supersonic turbulent laser-plasmas will also be discussed.