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1. Nonlinear susceptibilities for weakly turbulent magnetized plasma: Electrostatic approximation

   https://doi.org/10.1063/5.0190511  

   Yoon, Peter H (March 2024, Physics of Plasmas)

   The plasma weak turbulence theory is a perturbative nonlinear theory, which has been proven to be quite valid in a number of applications. However, the standard weak turbulence theory found in the literature is fully developed for highly idealized unmagnetized plasmas. As many plasmas found in nature and laboratory are immersed in a background static magnetic field, it is necessary to extend the existing discussions to include the effects of ambient magnetic field. Such a task is quite formidable, however, which has prevented fundamental and significant progresses in the subject matter. The central difficulty lies in the formulation of the complete nonlinear response functions for magnetized plasmas. The present paper derives the nonlinear susceptibilities for weakly turbulent magnetized plasmas up to the third order nonlinearity, but in doing so, a substantial reduction in mathematical complexity is achieved by the use of Bessel function addition theorem (or sum rule). The present paper also constructs the weak turbulence wave kinetic equation in a formal sense. For the sake of simplicity, however, the present paper assumes the electrostatic interaction among plasma particles. Fully electromagnetic generalization is a subject of a subsequent paper. 

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2. Two-fluid approach to weak plasma turbulence

   https://doi.org/10.1088/1361-6587/ac2e40  

   Yoon, Peter H (November 2021, Plasma Physics and Controlled Fusion)

   Abstract Weakly turbulent processes that take place in plasmas are customarily formulated in terms of kinetic theory. However, owing to an inherent complexity associated with the problem, thus far the theory is fully developed largely for unmagnetized plasmas. In the present paper it is shown that a warm two fluid theory can successfully be employed in order to partially formulate the weak turbulence theory in spatially uniform plasma. Specifically, it is shown that the nonlinear wave-wave interaction, or decay processes, can be reproduced by the two-fluid formalism. The present finding shows that the same approach can in principle be extended to magnetized plasmas, which is a subject of future work. 

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3. Strong suppression of heat conduction in a laboratory replica of galaxy-cluster turbulent plasmas

   https://doi.org/10.1126/sciadv.abj6799  

   Meinecke, Jena; Tzeferacos, Petros; Ross, James S.; Bott, Archie F.; Feister, Scott; Park, Hye-Sook; Bell, Anthony R.; Blandford, Roger; Berger, Richard L.; Bingham, Robert; et al (March 2022, Science Advances)

   Heat conduction is strongly suppressed in turbulent, weakly collisional, and magnetized plasmas. 

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4. Magneto-immutable turbulence in weakly collisional plasmas

   https://doi.org/10.1017/S0022377819000114  

   Squire, J.; Schekochihin, A. A.; Quataert, E.; Kunz, M. W. (February 2019, Journal of Plasma Physics)

   null (Ed.)

   We propose that pressure anisotropy causes weakly collisional turbulent plasmas to self-organize so as to resist changes in magnetic-field strength. We term this effect ‘magneto-immutability’ by analogy with incompressibility (resistance to changes in pressure). The effect is important when the pressure anisotropy becomes comparable to the magnetic pressure, suggesting that in collisionless, weakly magnetized (high- $$\unicode[STIX]{x1D6FD}$$ ) plasmas its dynamical relevance is similar to that of incompressibility. Simulations of magnetized turbulence using the weakly collisional Braginskii model show that magneto-immutable turbulence is surprisingly similar, in most statistical measures, to critically balanced magnetohydrodynamic turbulence. However, in order to minimize magnetic-field variation, the flow direction becomes more constrained than in magnetohydrodynamics, and the turbulence is more strongly dominated by magnetic energy (a non-zero ‘residual energy’). These effects represent key differences between pressure-anisotropic and fluid turbulence, and should be observable in the $$\unicode[STIX]{x1D6FD}\gtrsim 1$$ turbulent solar wind. 

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5. Insensitivity of a turbulent laser-plasma dynamo to initial conditions

   https://doi.org/10.1063/5.0084345  

   Bott, A. F.; Chen, L.; Tzeferacos, P.; Palmer, C. A.; Bell, A. R.; Bingham, R.; Birkel, A.; Froula, D. H.; Katz, J.; Kunz, M. W.; et al (July 2022, Matter and Radiation at Extremes)

   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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