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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 self-emission 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.
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This content will become publicly available on June 1, 2027
Self-ordering to imposed ordering of dust—A continuous spatial phase transition experiment in MDPX
Previous experiments conducted in the Magnetized Dusty Plasma eXperiment revealed an intriguing phenomenon first referred to as imposed ordering. This occurs when micrometer-sized dust particles become aligned with the geometry of a conducting mesh placed above the dust (at a distance much larger than the plasma Debye length or the ion–neutral or electron–neutral mean free paths) in the presence of a strong magnetic field perpendicular to the mesh. In this work, results of a transition experiment are presented wherein starting from a classical two-dimensional Coulomb crystal with hexagonal symmetry in an unmagnetized plasma (B=0 T), dust transitions to a state in which it flows along the geometry of a conducting mesh placed above it, mapping out the fourfold symmetry of the boundary condition. It is hypothesized that beyond a certain magnetization, elongated electric potential structures emanating from the mesh grow strong enough to drive the dust motion to reflect the mesh morphology, gradually transitioning from a sixfold self-ordering to fourfold imposed ordering. The various dust phases are quantified, and a critical value of magnetic field is identified in the transition experiment, indicating the onset of imposed ordering over the whole dust cloud.
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- PAR ID:
- 10700579
- Publisher / Repository:
- American Institute of Physics
- Date Published:
- Journal Name:
- Physics of Plasmas
- Volume:
- 33
- Issue:
- 6
- ISSN:
- 1070-664X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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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. https://doi.org/10.1063/5.0084345more » « less
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