DOI: 10.7910/dvn/usbogq
title: Time-resolved turbulent dynamo in a laser plasma

description: Understanding magnetic-field generation and amplification in turbulent plasma is essential to account for observations of magnetic fields in the universe. A theoretical framework attributing the origin and sustainment of these fields to the so-called fluctuation dynamo was recently validated by experiments on laser facilities in low-magnetic-Prandtl-number plasmas (Pm&lt;1). However, the same framework proposes that the fluctuation dynamo should operate differently when Pm≳1, the regime relevant to many astrophysical environments such as the intracluster medium of galaxy clusters. This paper reports an experiment that creates a laboratory Pm≳1 plasma dynamo. We provide a time-resolved characterization of the plasma’s evolution, measuring temperatures, densities, flow velocities, and magnetic fields, which allows us to explore various stages of the fluctuation dynamo’s operation on seed magnetic fields generated by the action of the Biermann-battery mechanism during the initial drive-laser target interaction. The magnetic energy in structures with characteristic scales close to the driving scale of the stochastic motions is found to increase by almost three orders of magnitude and saturate dynamically. It is shown that the initial growth of these fields occurs at a much greater rate than the turnover rate of the driving-scale stochastic motions. Our results point to the possibility that plasma turbulence produced by strong shear can generate fields more efficiently at the driving scale than anticipated by idealized magnetohydrodynamics (MHD) simulations of the nonhelical fluctuation dynamo; this finding could help explain the large-scale fields inferred from observations of astrophysical systems.
description: PSFC REPORT PSFC/JA-21-17<br><br>The research leading to these results has received funding from the European Research Council under the European Community’s Seventh Framework Program (FP7/2007-2013)/ERC Grants 256973 and 247039; the US Department of Energy (DOE) National Nuclear Security Administration under Contract B591485 to Lawrence Livermore National Laboratory (LLNL); Field Work Proposal 57789 to Argonne National Laboratory (ANL); Subcontract 536203 with Los Alamos National Laboratory; Subcontract B632670 with LLNL; Grants DE-NA0002724, DE-NA0003605, and DE-NA0003934 to the University of Chicago; Grant DE-NA0003868 to the Massachusetts Institute of Technology; and Cooperative Agreement DE-NA0003856 to the Laboratory for Laser Energetics, University of Rochester. We acknowledge support from the US DOE Office of Science Fusion Energy Sciences under Grant DE-SC0016566 and the National Science Foundation under Grants PHY-1619573, PHY-2033925, and AST-1908551. Awards of computer time were provided by the US DOE Advanced Scientific Computing Research Leadership Computing Challenge program, using resources at ANL, which is supported by the US DOE Office of Science under Contract DE-AC02-06CH11357. We acknowledge funding from Grants 2016R1A5A1013277 and 2017R1A2A1A05071429 of the National Research Foundation of Korea. Support from Atomic Weapons Establishment plc., the Engineering and Physical Sciences Research Council (Grants EP/M022331/1, EP/N014472/1, and EP/R034737/1), and the UK Science and Technology Facilities Council is also acknowledged.<br><br>If this record does not contain the full text, then the manuscript has been embargoed by the publisher thus restricting open access for 12 to 24 months after publication.