It has recently been demonstrated experimentally that a turbulent plasma created by the collision of two inhomogeneous,asymmetric,weakly magnetized,laser-produced plasma jets can generate strong stochastic magnetic fi...It has recently been demonstrated experimentally that a turbulent plasma created by the collision of two inhomogeneous,asymmetric,weakly magnetized,laser-produced plasma jets can generate strong stochastic magnetic fields via the small-scale turbulent dynamo mechanism,provided the magnetic Reynolds number of the plasma is sufficiently large.In this paper,we compare such a plasma with one arising from two pre-magnetized plasma jets whose creation is identical save for the addition of a strong external magnetic field imposed by a pulsed magnetic field generator.We investigate the differences between the two turbulent systems using a Thomson-scattering diagnostic,x-ray selfemission imaging,and proton radiography.The Thomson-scattering spectra and x-ray images suggest that the external magnetic field has a limited effect on the plasma dynamics in the experiment.Although the external magnetic field induces collimation of the flows in the colliding plasma jets and although the initial strengths of the magnetic fields arising from the interaction between the colliding jets are significantly larger as a result of the external field,the energies and morphologies of the stochastic magnetic fields post-amplification are indistinguishable.We conclude that,for turbulent laser-plasmas with supercritical magnetic Reynolds numbers,the dynamo-amplified magnetic fields are determined by the turbulent dynamics rather than the seed fields or modest changes in the initial flow dynamics of the plasma,a finding consistent with theoretical expectations and simulations of turbulent dynamos.展开更多
基金the European Research Council(ERC)under the European Community’s Seventh Framework Programme(Grant No.FP7/2007-2013,ERC Grant Agreement Nos.256973 and 247039)the National Nuclear Security Administration(NNSA)of the U.S.Department of Energy(DOE)under Contract No.B591485+12 种基金Lawrence Livermore National Laboratory(LLNL),Field Work Proposal No.57789Argonne National Laboratory,Subcontract Nos.536203 and 630138Los Alamos National Laboratory,Subcontract No.B632670LLNL,Grant Nos.DE-NA0002724,DE-NA0003605,and DE-NA0003934the Flash Center for Computational Science,Grant No.DE-NA0003868the Massachusetts Institute of Technology,and Cooperative Agreement No.DE-NA0003856the Laboratory for Laser Energetics at the University of Rochester.the U.S.DOE Office of Science Fusion Energy Sciences(Grant No.DE-SC0016566)the National Science Foundation(Grant Nos.PHY-1619573,PHY-2033925,and PHY-2045718)the National Research Foundation of Korea(Grant Nos.2016R1A5A1013277 and 2020R1A2C2102800)Support from AWE plc.,the Engineering and Physical Sciences Research Council(Grant Nos.EP/M022331/1,EP/N014472/1,and EP/R034737/1)the U.K.Science and Technology Facilities Council is also acknowledged.General Atomics for target manufacturing and R&D support,which was funded by the NNSA in support of the National Laser Users’Facility program(Subcontract Nos.89233118CNA000010 and 89233119CNA000063).
文摘It has recently been demonstrated experimentally that a turbulent plasma created by the collision of two inhomogeneous,asymmetric,weakly magnetized,laser-produced plasma jets can generate strong stochastic magnetic fields via the small-scale turbulent dynamo mechanism,provided the magnetic Reynolds number of the plasma is sufficiently large.In this paper,we compare such a plasma with one arising from two pre-magnetized plasma jets whose creation is identical save for the addition of a strong external magnetic field imposed by a pulsed magnetic field generator.We investigate the differences between the two turbulent systems using a Thomson-scattering diagnostic,x-ray selfemission imaging,and proton radiography.The Thomson-scattering spectra and x-ray images suggest that the external magnetic field has a limited effect on the plasma dynamics in the experiment.Although the external magnetic field induces collimation of the flows in the colliding plasma jets and although the initial strengths of the magnetic fields arising from the interaction between the colliding jets are significantly larger as a result of the external field,the energies and morphologies of the stochastic magnetic fields post-amplification are indistinguishable.We conclude that,for turbulent laser-plasmas with supercritical magnetic Reynolds numbers,the dynamo-amplified magnetic fields are determined by the turbulent dynamics rather than the seed fields or modest changes in the initial flow dynamics of the plasma,a finding consistent with theoretical expectations and simulations of turbulent dynamos.
