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

Meinecke, J.; Tzeferacos, Petros; Ross, J. S.; Bott, A. F. A.; Feister, Scott; Park, Hye-Sook; Bell, A. R.; Blandford, R. D.; Berger, R. L.; Bingham, R.; Casner, A.; Chen, Laura E.; Foster, J. M.; Froula, D. H.; Goyon, C.; Kalantar, D. H.; Kœnig, M.; Lahmann, B.; Li, C. K.; Lu, Yingchao; Palmer, C. A. J.; Petrasso, R. D.; Poole, Hannah; Remington, B. A.; Reville, Brian; Reyes, Adam; Rigby, A.; Ryu, Dongsu; Swadling, G. F.; Zylstra, A. B.; Miniati, Francesco; Sarkar, S.; Schekochihin, A. A.; Lamb, D. Q.; Gregori, G.

doi:10.1126/sciadv.abj6799

Cited by 18 publications

(12 citation statements)

References 47 publications

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“…41 Most recently, a turbulent laser-plasma with Rm ≈ 3500 and Pm ≈ 10 was successfully produced at the National Ignition Facility, with dynamo-amplified magnetic fields of megagauss strengths being observed. 42 One finding of previous turbulent-dynamo experiments that merited further study was that the ratio of the magnetic to turbulent kinetic energy density was observed to be finite but still quite small (ε B /ε K,turb ≈ 3%-4%). 37,38 This prompted the question of whether the characteristic post-amplification strength of the magnetic fields in these turbulent laser-plasmas is determined by only the turbulent kinetic energy of the plasma or was, in fact, not dynamical and, thus, might be expected to be larger in a stronger initial magnetic field.…”

Section: Research Articlementioning

confidence: 95%

Insensitivity of a turbulent laser-plasma dynamo to initial conditions

Bott

Chen

Tzeferacos

et al. 2022

Matter and Radiation at Extremes

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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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Section: Research Articlementioning

confidence: 95%

Insensitivity of a turbulent laser-plasma dynamo to initial conditions

Bott

Chen

Tzeferacos

et al. 2022

Matter and Radiation at Extremes

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“…The parameters for the laser-ablated carbon-hydrogen plasma are from an experiment on the OMEGA laser facility, with a 1 ns, 500 J pulse with a 0.351 μm wavelength (Li et al 2007); we assume that the measured fields are found in front of the critical-density surface when estimating the density. The 'TDYNO' laser plasma is a turbulent carbon-hydrogen plasma that was produced as part of a recent laboratory astrophysics experiment on the NIF which found evidence of suppressed heat conduction (Meinecke et al 2022). Naturally, the systems described here often support a range of density, temperatures and magnetic fields, so the values provided should be understood as representative, but negotiable.…”

Section: Microinstabilitymentioning

confidence: 99%

“…Similar considerations apply to a range of laser plasmas, including plasmas generated in inertial-confinement-fusion and laboratory-astrophysics experiments. Indeed, a recent experiment carried out on the National Ignition Facility (NIF) -part of a wider programme of work exploring magnetic-field amplification in turbulent laser plasmas (Tzeferacos et al 2018;Bott et al 2021cBott et al ,b, 2022 -found evidence for the existence of large-amplitude local temperature fluctuations over a range of scales, a finding that was inconsistent with Spitzer thermal conduction (Meinecke et al 2022). This claim was corroborated by magnetohydrodynamic (MHD) simulations (with the code FLASH) of the experiment that modelled thermal conduction either using the Spitzer model, or no explicit thermal conduction model: the latter simulations were found to be much closer to the actual experimental data.…”

Section: Microinstabilitymentioning

confidence: 99%

Kinetic stability of Chapman–Enskog plasmas

Bott,

Cowley,

Schekochihin

2024

J. Plasma Phys.

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In this paper, we investigate the kinetic stability of classical, collisional plasma – that is, plasma in which the mean-free-path $\lambda$ of constituent particles is short compared with the length scale $L$ over which fields and bulk motions in the plasma vary macroscopically, and the collision time is short compared with the evolution time. Fluid equations are typically used to describe such plasmas, since their distribution functions are close to being Maxwellian. The small deviations from the Maxwellian distribution are calculated via the Chapman–Enskog (CE) expansion in $\lambda /L \ll 1$ , and determine macroscopic momentum and heat fluxes in the plasma. Such a calculation is only valid if the underlying CE distribution function is stable at collisionless length scales and/or time scales. We find that at sufficiently high plasma $\beta$ , the CE distribution function can be subject to numerous microinstabilities across a wide range of scales. For a particular form of the CE distribution function arising in strongly magnetised plasma (viz. plasma in which the Larmor periods of particles are much smaller than collision times), we provide a detailed analytic characterisation of all significant microinstabilities, including peak growth rates and their associated wavenumbers. Of specific note is the discovery of several new microinstabilities, including one at sub-electron-Larmor scales (the ‘whisper instability’) whose growth rate in certain parameter regimes is large compared with other instabilities. Our approach enables us to construct the kinetic stability maps of classical, two-species collisional plasma in terms of $\lambda$ , the electron inertial scale $d_e$ and the plasma $\beta$ . This work is of general consequence in emphasising the fact that high- $\beta$ collisional plasmas can be kinetically unstable; for strongly magnetised CE plasmas, the condition for instability is $\beta \gtrsim L/\lambda$ . In this situation, the determination of transport coefficients via the standard CE approach is not valid.

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“…For this study, capillary discharge behavior is examined via fully resolved magneto-hydrodynamics simulations performed using the FLASH code. FLASH 24 is a publicly available 26 , parallel, multi-physics, adaptivemesh-refinement, finite-volume Eulerian hydrodynamics and MHD 27 code, whose high energy density physics capabilities 25 and synthetic diagnostics 28 have been validated through benchmarks and code-to-code comparisons 29,30 , as well as through direct application to laserdriven laboratory experiments [31][32][33][34][35][36][37][38] .…”

Section: Magnetohydrodynamics Modelmentioning

confidence: 99%

Impact of Electron Transport Models on Capillary Discharge Plasmas

Diaw,

Coleman,

Cook

et al. 2022

Preprint

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Magnetohydrodynamics (MHD) can be used to model capillary discharge waveguides in laser-wakefield accelerators. However, the predictive capability of MHD can suffer due to poor microscopic closure models. Here, we study the impact of electron heating and thermal conduction on capillary waveguide performance as part of an effort to understand and quantify uncertainties in modeling and designing next-generation plasma accelerators. To do so, we perform two-dimensional high-resolution MHD simulations using an argon-filled capillary discharge waveguide with three different electron transport coefficients models. The models tested include (i) Davies et al. (ii) Spitzer, and (iii) Epperlein-Haines (EH). We found that the EH model overestimates the electron temperature inside the channel by over 20% while predicting a lower azimuthal magnetic field. Moreover, the Spitzer model, often used in MHD simulations for plasma-based accelerators, predicts a significantly higher electron temperature than the other models suggest.

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

Cited by 18 publications

References 47 publications

Insensitivity of a turbulent laser-plasma dynamo to initial conditions

Insensitivity of a turbulent laser-plasma dynamo to initial conditions

Kinetic stability of Chapman–Enskog plasmas

Impact of Electron Transport Models on Capillary Discharge Plasmas

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