Spectral evolution of helical electron magnetohydrodynamic turbulence

Cho, Jungyeon; Kim, Hoonkyu

doi:10.1002/2016ja022364

Cited by 10 publications

(11 citation statements)

References 39 publications

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“…2018), as argued on the basis of a Fjørtoft (1953) argument in HRMHD (Schekochihin et al. 2009) and observed in the numerical simulations of EMHD (Cho & Kim 2016). In contrast, if the energy spectra are prescribed at large scales, the transfer rates can adjust freely.…”

Section: Resultsmentioning

confidence: 70%

“…Differently, if the dissipation scale is smaller than the ion transition scale where dispersion starts acting, the above model displays unphysical features. This results from the conflict between a prescribed cross-helicity flux in the forward direction and the tendency of the cross-helicity which, at the dispersive scales, identifies with the magnetic helicity, to undergo an inverse cascade Passot et al 2018), as argued on the basis of a Fjørtoft (1953) argument in HRMHD (Schekochihin et al 2009) and observed in the numerical simulations of EMHD (Cho & Kim 2016). In contrast, if the energy spectra are prescribed at large scales, the transfer rates can adjust freely.…”

Section: Resultsmentioning

confidence: 99%

“…An interesting question is whether dissipation and pinning still play a crucial role in the presence of dispersive effects. In this context, it is worth mentioning that pinning was recently observed in direct simulations of three-dimensional EMHD displaying a direct energy cascade and an inverse cascade of magnetic helicity (Cho & Kim 2016).…”

Section: Introductionmentioning

confidence: 81%

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Imbalanced kinetic Alfvén wave turbulence: from weak turbulence theory to nonlinear diffusion models for the strong regime

Passot

Sulem

2019

J. Plasma Phys.

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A two-field Hamiltonian gyrofluid model for kinetic Alfvén waves retaining ion finite Larmor radius corrections, parallel magnetic field fluctuations and electron inertia, is used to study turbulent cascades from the MHD to the sub-ion scales. Special attention is paid to the case of imbalance between waves propagating along or opposite to the ambient magnetic field. For weak turbulence in the absence of electron inertia, kinetic equations for the spectral density of the conserved quantities (total energy and generalized crosshelicity) are obtained. They provide a global description, matching between the regimes of reduced MHD at large scales and electron reduced MHD at small scales, previously considered in the literature. In the limit of ultra-local interactions, Leith-type nonlinear diffusion equations in the Fourier space are derived and heuristically extended to the strong turbulence regime by modifying the transfer time appropriately. Relations with existing phenomenological models for imbalanced MHD and balanced sub-ion turbulence are discussed. It turns out that in the presence of dispersive effects, the dynamics is sensitive on the way turbulence is maintained in a steady state. Furthermore, the total energy spectrum at sub-ion scales becomes steeper as the generalized cross-helicity flux is increased.

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Section: Resultsmentioning

confidence: 70%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 81%

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Imbalanced kinetic Alfvén wave turbulence: from weak turbulence theory to nonlinear diffusion models for the strong regime

Passot

Sulem

2019

J. Plasma Phys.

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“…The presence of extra invariants does open the possibility of dual or even triple cascades in Hall-RMHD turbulence: in particular, will cascade to larger scales if it is injected at small scales (see S09–§ F.6; Cho & Kim 2016 and references therein), whereas is expected to cascade forward, together with the free energy (Chen, Chen & Eyink 2003; Banerjee & Galtier 2016). Thus, the Hall-RMHD system can offer some considerable rewards to a devoted turbulence theorist.…”

Section: Reduced Dynamics and Heating In The Hall Limitmentioning

confidence: 99%

Constraints on ion versus electron heating by plasma turbulence at low beta

Schekochihin

Kawazura²,

Barnes

2019

J. Plasma Phys.

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It is shown that in low-beta, weakly collisional plasmas, such as the solar corona, some instances of the solar wind, the aurora, inner regions of accretion discs, their coronae, and some laboratory plasmas, Alfvénic fluctuations produce no ion heating within the gyrokinetic approximation, i.e., as long as their amplitudes (at the Larmor scale) are small and their frequencies stay below the ion Larmor frequency (even as their spatial scales can be above or below the ion Larmor scale). Thus, all low-frequency ion heating in such plasmas is due to compressive fluctuations ("slow modes"): density perturbations and non-Maxwellian perturbations of the ion distribution function. Because these fluctuations energetically decouple from the Alfvénic ones already in the inertial range, the above conclusion means that the energy partition between ions and electrons in low-beta plasmas is decided at the outer scale, where turbulence is launched, and can be determined from magnetohydrodynamic (MHD) models of the relevant astrophysical systems. Any additional ion heating must come from non-gyrokinetic mechanisms such as cyclotron heating or the stochastic heating owing to distortions of ions' Larmor orbits. An exception to these conclusions occurs in the Hall limit, i.e., when the ratio of the ion to electron temperatures is as low as the ion beta (equivalently, the electron beta is order unity). In this regime, slow modes couple to Alfvénic ones well above the Larmor scale (viz., at the ion inertial or ion sound scale), so the Alfvénic and compressive cascades join and then separate again into two cascades of fluctuations that linearly resemble kinetic Alfvén and ion cyclotron waves, with the former heating electrons and the latter ions. The two cascades are shown to decouple, scalings for them are derived, and it is argued physically that the two species will be heated by them at approximately equal rates. †

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“…Numerical attempts to model imbalanced turbulence in the MHD regime have proven difficult due to questions about the effects of varying dissipation prescriptions, limited dynamic ranges of accessible simulation domains, and limited run times (Beresnyak & Lazarian 2009Perez & Boldyrev 2010b,a;Perez et al 2012;Mason et al 2012). Some studies have extended beyond standard MHD to the relativistic MHD regime 𝜎 1 (Cho & Lazarian 2014;Kim & Cho 2015), made approximations of large ion-to-electron mass ratio to model scales below the proton gyroradius (Cho & Kim 2016) or to capture finite Larmor radius effects (Meyrand et al 2020), or employed a diffusive model to study turbulence from fluid to sub-ion scales (Miloshevich et al 2020). However, few numerical studies have modeled the fully kinetic collisionless regime-those with an eye towards the solar wind (Grošelj et al 2018)-and none to our knowledge have examined the ultrarelativistic, collisionless regime relevant to highenergy astrophysical systems.…”

Section: Introductionmentioning

confidence: 99%

Kinetic Simulations of Imbalanced Turbulence in a Relativistic Plasma: Net Flow and Particle Acceleration

Hankla,

Zhdankin,

Werner

et al. 2021

Preprint

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Turbulent high-energy astrophysical systems often feature asymmetric energy injection or driving: for instance, nonlinear interactions between Alfvén waves propagating from an accretion disk into its corona. Such systems-relativistic analogs of the solar wind-are "imbalanced": the energy fluxes parallel and anti-parallel to the large-scale magnetic field are unequal and the plasma therefore possesses net cross-helicity. In the past, numerical studies of imbalanced turbulence have focused on the magnetohydrodynamic regime. In the present study, we investigate externally-driven imbalanced turbulence in a collisionless, ultrarelativistically hot, magnetized pair plasma using three-dimensional particle-in-cell simulations. We find that a turbulent cascade forms for every value of imbalance covered by the simulations and that injected Poynting flux efficiently converts into net momentum of the plasma, a relativistic effect with implications for the launching of a disk wind. Surprisingly, particle acceleration remains efficient even for very imbalanced turbulence. These results characterize properties of imbalanced turbulence in a collisionless plasma and have ramifications for black hole accretion disk coronae, winds, and jets.

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Spectral evolution of helical electron magnetohydrodynamic turbulence

Cited by 10 publications

References 39 publications

Imbalanced kinetic Alfvén wave turbulence: from weak turbulence theory to nonlinear diffusion models for the strong regime

Imbalanced kinetic Alfvén wave turbulence: from weak turbulence theory to nonlinear diffusion models for the strong regime

Constraints on ion versus electron heating by plasma turbulence at low beta

Kinetic Simulations of Imbalanced Turbulence in a Relativistic Plasma: Net Flow and Particle Acceleration

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