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
We have developed a new radiography setup with a short-pulse laser-driven x-ray source. Using a radiography axis perpendicular to both long- and short-pulse lasers allowed optimizing the incident angle of the short-pu...We have developed a new radiography setup with a short-pulse laser-driven x-ray source. Using a radiography axis perpendicular to both long- and short-pulse lasers allowed optimizing the incident angle of the short-pulse laser on the x-ray source target. The setup has been tested with various x-ray source target materials and different laser wavelengths.Signal to noise ratios are presented as well as achieved spatial resolutions. The high quality of our technique is illustrated on a plasma flow radiograph obtained during a laboratory astrophysics experiment on POLARs.展开更多
This paper describes a model of electron energization and cyclotron-maser emission applicable to astrophysical magnetized collisionless shocks. It is motivated by the work of Begelman, Ergun and Rees [Astrophys. J. 62...This paper describes a model of electron energization and cyclotron-maser emission applicable to astrophysical magnetized collisionless shocks. It is motivated by the work of Begelman, Ergun and Rees [Astrophys. J. 625, 51(2005)] who argued that the cyclotron-maser instability occurs in localized magnetized collisionless shocks such as those expected in blazar jets. We report on recent research carried out to investigate electron acceleration at collisionless shocks and maser radiation associated with the accelerated electrons. We describe how electrons accelerated by lower-hybrid waves at collisionless shocks generate cyclotron-maser radiation when the accelerated electrons move into regions of stronger magnetic fields. The electrons are accelerated along the magnetic field and magnetically compressed leading to the formation of an electron velocity distribution having a horseshoe shape due to conservation of the electron magnetic moment. Under certain conditions the horseshoe electron velocity distribution function is unstable to the cyclotron-maser instability [Bingham and Cairns, Phys. Plasmas 7, 3089(2000); Melrose, Rev. Mod. Plasma Phys. 1, 5(2017)].展开更多
In this paper, we present a model characterizing the interaction of a radiative shock(RS) with a solid material, as described in a recent paper(Koenig et al., Phys. Plasmas, 24, 082707(2017)), the new model is then re...In this paper, we present a model characterizing the interaction of a radiative shock(RS) with a solid material, as described in a recent paper(Koenig et al., Phys. Plasmas, 24, 082707(2017)), the new model is then related to recent experiments performed on the GEKKO XII laser facility. The RS generated in a xenon gas cell propagates towards a solid obstacle that is ablated by radiation coming from the shock front and the radiative precursor, mimicking processes occurring in astrophysical phenomena. The model presented here calculates the dynamics of the obstacle expansion,which depends on several parameters, notably the geometry and the temperature of the shock. All parameters required for the model have been obtained from experiments. Good agreement between experimental data and the model is found when spherical geometry is taken into account. As a consequence, this model is a useful and easy tool to infer parameters from experimental data(such as the shock temperature), and also to design future experiments.展开更多
Magnetic field measurements in turbulent plasmas are often difficult to perform. Here we show that for kG magnetic fields, a time-resolved Faraday rotation measurement can be made at the OMEGA laser facility. This dia...Magnetic field measurements in turbulent plasmas are often difficult to perform. Here we show that for kG magnetic fields, a time-resolved Faraday rotation measurement can be made at the OMEGA laser facility. This diagnostic has been implemented using the Thomson scattering probe beam and the resultant path-integrated magnetic field has been compared with that of proton radiography. Accurate measurement of magnetic fields is essential for satisfying the scientific goals of many current laser–plasma experiments.展开更多
In this paper we present a high repetition rate experimental platform for examining the spatial structure and evolution of Biermann-generated magnetic fields in laser-produced plasmas.We have extended the work of prio...In this paper we present a high repetition rate experimental platform for examining the spatial structure and evolution of Biermann-generated magnetic fields in laser-produced plasmas.We have extended the work of prior experiments,which spanned over millimeter scales,by spatially measuring magnetic fields in multiple planes on centimeter scales over thousands of laser shots.Measurements with magnetic fiux probes show azimuthally symmetric magnetic fields that range from 60 G at 0.7 cm from the target to 7 G at 4.2 cm from the target.The expansion rate of the magnetic fields and evolution of current density structures are also mapped and examined.Electron temperature and density of the laser-produced plasma are measured with optical Thomson scattering and used to directly calculate a magnetic Reynolds number of 1.4×10^(4),confirming that magnetic advection is dominant at≥1.5 cm from the target surface.The results are compared to FLASH simulations,which show qualitative agreement with the data.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.
基金the support of RFBR grant 14-29-06099Competitiveness Programme of NRNU MEPhI
文摘We have developed a new radiography setup with a short-pulse laser-driven x-ray source. Using a radiography axis perpendicular to both long- and short-pulse lasers allowed optimizing the incident angle of the short-pulse laser on the x-ray source target. The setup has been tested with various x-ray source target materials and different laser wavelengths.Signal to noise ratios are presented as well as achieved spatial resolutions. The high quality of our technique is illustrated on a plasma flow radiograph obtained during a laboratory astrophysics experiment on POLARs.
基金funding from the Engineering and Physical Sciences Research Council(grant Nos.EP/N014472/1,EP/R004773/1and EP/N013298/1)the Science and Technologies Facilities Council of the United Kingdom.F.C.+2 种基金support from the European Research Council(InPairs ERC-2015-AdG 695088)FCT Portugal(grant No.PD/BD/114307/2016)supported in part at the University of Chicago by the US DOE NNSA ASC through the Argonne Institute for Computing in Science under FWP 57789 and the US DOE Office of Science through grant No.DE-SC0016566
文摘This paper describes a model of electron energization and cyclotron-maser emission applicable to astrophysical magnetized collisionless shocks. It is motivated by the work of Begelman, Ergun and Rees [Astrophys. J. 625, 51(2005)] who argued that the cyclotron-maser instability occurs in localized magnetized collisionless shocks such as those expected in blazar jets. We report on recent research carried out to investigate electron acceleration at collisionless shocks and maser radiation associated with the accelerated electrons. We describe how electrons accelerated by lower-hybrid waves at collisionless shocks generate cyclotron-maser radiation when the accelerated electrons move into regions of stronger magnetic fields. The electrons are accelerated along the magnetic field and magnetically compressed leading to the formation of an electron velocity distribution having a horseshoe shape due to conservation of the electron magnetic moment. Under certain conditions the horseshoe electron velocity distribution function is unstable to the cyclotron-maser instability [Bingham and Cairns, Phys. Plasmas 7, 3089(2000); Melrose, Rev. Mod. Plasma Phys. 1, 5(2017)].
基金supported by the Scientific Council of the Observatoire de Parisby COST(European COoperation in Science and Technology),action MP1208,with a Short-Term Scientific Mission
文摘In this paper, we present a model characterizing the interaction of a radiative shock(RS) with a solid material, as described in a recent paper(Koenig et al., Phys. Plasmas, 24, 082707(2017)), the new model is then related to recent experiments performed on the GEKKO XII laser facility. The RS generated in a xenon gas cell propagates towards a solid obstacle that is ablated by radiation coming from the shock front and the radiative precursor, mimicking processes occurring in astrophysical phenomena. The model presented here calculates the dynamics of the obstacle expansion,which depends on several parameters, notably the geometry and the temperature of the shock. All parameters required for the model have been obtained from experiments. Good agreement between experimental data and the model is found when spherical geometry is taken into account. As a consequence, this model is a useful and easy tool to infer parameters from experimental data(such as the shock temperature), and also to design future experiments.
基金funding from the European Research Council under the European Community Seventh Framework Programme(FP7/2007-2013)/ERC grant agreement No.256973the U.S.Department of Energy under Contract No.B591485 to Lawrence Livermore National Laboratory,Field Work Proposal No.57789 to Argonne National Laboratory,grant Nos.DE-NA0002724and DE-SC0016566 to the University of Chicago,and Cooperative Agreement DE-NA0001944 to the Laboratory for Laser Energetics University of Rochester+5 种基金support from the National Science Foundation under grant PHY-1619573supported in part by National Institutes of Health through resources provided by the Computation Institute and the Biological Sciences Division of the University of Chicago and Argonne National Laboratory,under grant S10 RR029030-01the U.S.Department of Energy Innovative and Novel Computational Impact on Theory and Experiment(INCITE)and ASCR Leadership Computing Challenge(ALCC)programmessupported by the Office of Science of the U.S.Department of Energy under contract DE-AC02-06CH11357Support from AWE plc.,the Engineering and Physical Sciences Research Council(grant Nos.EP/M022331/1 and EP/N014472/1)the Science and Technology Facilities Council of the United Kingdom is acknowledged
文摘Magnetic field measurements in turbulent plasmas are often difficult to perform. Here we show that for kG magnetic fields, a time-resolved Faraday rotation measurement can be made at the OMEGA laser facility. This diagnostic has been implemented using the Thomson scattering probe beam and the resultant path-integrated magnetic field has been compared with that of proton radiography. Accurate measurement of magnetic fields is essential for satisfying the scientific goals of many current laser–plasma experiments.
基金the Department of Energy(DOE)under award number DE-SC0019011the National Nuclear Security Administration(NNSA)Center for Matter under Extreme Conditions under award number DE-NA0003842+1 种基金the National Science Foundation Graduate Fellowship Research Program under award number DGE-1650604support by the U.S.DOE NNSA under Subcontracts 536203 and 630138 with Los Alamos National Laboratory,Subcontract B632670 with LLNL and support from the Cooperative Agreement DE-NA0003856 to the Laboratory for Laser Energetics University of Rochester。
文摘In this paper we present a high repetition rate experimental platform for examining the spatial structure and evolution of Biermann-generated magnetic fields in laser-produced plasmas.We have extended the work of prior experiments,which spanned over millimeter scales,by spatially measuring magnetic fields in multiple planes on centimeter scales over thousands of laser shots.Measurements with magnetic fiux probes show azimuthally symmetric magnetic fields that range from 60 G at 0.7 cm from the target to 7 G at 4.2 cm from the target.The expansion rate of the magnetic fields and evolution of current density structures are also mapped and examined.Electron temperature and density of the laser-produced plasma are measured with optical Thomson scattering and used to directly calculate a magnetic Reynolds number of 1.4×10^(4),confirming that magnetic advection is dominant at≥1.5 cm from the target surface.The results are compared to FLASH simulations,which show qualitative agreement with the data.