Spectrum of Kinetic-Alfvén Turbulence

Boldyrev, Stanislav; Perez, Jean C.

doi:10.1088/2041-8205/758/2/l44

Cited by 178 publications

(273 citation statements)

References 36 publications

(97 reference statements)

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“…Unlike the inertial range, the nature of the turbulence in the dissipation range is still under debate. Two possible scenarios include Landau damping of kinetic Alfvén waves (KAWs; e.g., Leamon et al 1999Leamon et al , 2000Boldyrev & Perez 2012) or whistler waves (e.g., Stawicki et al 2001;Krishan & Mahajan 2004;Galtier 2006). For KAWs, k ⊥ k || , electron-wave interaction occurs through the Landau resonance and KAWs can effectively heat electrons.…”

Section: Diffusive Shock Acceleration Of Electrons At a Finite-width mentioning

confidence: 99%

ON THE SPECTRAL HARDENING AT ≳300 keV IN SOLAR FLARES

Kong

Zank

et al. 2013

ApJ

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It has long been noted that the spectra of observed continuum emissions in many solar flares are consistent with double power laws with a hardening at energies 300 keV. It is now widely believed that at least in electrondominated events, the hardening in the photon spectrum reflects an intrinsic hardening in the source electron spectrum. In this paper, we point out that a power-law spectrum of electrons with a hardening at high energies can be explained by the diffusive shock acceleration of electrons at a termination shock with a finite width. Our suggestion is based on an early analytical work by Drury et al., where the steady-state transport equation at a shock with a tanh profile was solved for a p-independent diffusion coefficient. Numerical simulations with a p-dependent diffusion coefficient show hardenings in the accelerated electron spectrum that are comparable with observations. One necessary condition for our proposed scenario to work is that high-energy electrons resonate with the inertial range of the MHD turbulence and low-energy electrons resonate with the dissipation range of the MHD turbulence at the acceleration site, and the spectrum of the dissipation range ∼k −2.7 . A ∼ k −2.7 dissipation range spectrum is consistent with recent solar wind observations.

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Section: Diffusive Shock Acceleration Of Electrons At a Finite-width mentioning

confidence: 99%

ON THE SPECTRAL HARDENING AT ≳300 keV IN SOLAR FLARES

Kong

Zank

et al. 2013

ApJ

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“…(1) the nature of the plasma modes that carry the turbulent cascade down to electron scales-kinetic Alfvén wave or whistler and/or another type of turbulence (Sahraoui et al , 2010(Sahraoui et al , 2012Schekochihin et al 2009;Boldyrev & Perez 2012;Gary et al 2012;Podesta & TenBarge 2012;Chen et al 2013;Podesta 2013). Nevertheless, recent studies(e.g., Chen et al 2013;Podesta 2013) suggest that whistler turbulence, if present at subproton scales, contributes to only a small fraction of fluctuation energy; (2) the nature of the dissipative processes (Schekochihin et al 2009;Sahraoui et al 2010); and (3) the shape of the magnetic energy spectra-power law (Sahraoui et al , 2010 or exponential (Alexandrova et al 2012).…”

Section: Introductionmentioning

confidence: 99%

Density Fluctuations Upstream and Downstream of Interplanetary Shocks

Pitňa

Šafránková

Němeček

et al. 2016

ApJ

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Interplanetary (IP) shocks as typical large-scale disturbances arising fromprocesses such asstream-stream interactions or Interplanetary Coronal Mass Ejection (ICME) launching play a significant role in the energy redistribution, dissipation, particle heating, acceleration, etc. They can change the properties of the turbulent cascade on shorter scales. We focus on changes of the level and spectral properties of ion flux fluctuations upstream and downstream of fastforward oblique shocks. Although the fluctuation level increases by an order of magnitude across the shock, the spectral slope in the magnetohydrodynamic range is conserved. The frequency spectra upstream of IP shocks are the same as those in the solar wind (if not spoiled by foreshock waves). The spectral slopes downstream are roughly proportional to the corresponding slopes upstream, suggesting that the properties of the turbulent cascade are conserved across the shock;thus, the shock does not destroy the shape of the spectrum as turbulence passes through it. Frequency spectra downstream of IP shocks often exhibit "an exponential decay" in the ion kinetic range that was earlier reported at electron scales in the solar wind or at ion scales in the interstellar medium. We suggest that the exponential shape of ion flux spectra in this range is caused by stronger damping of the fluctuations in the downstream region.

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“…The kinetic Alfvén wave and whistler fluctuations are likely to make an important contribution to the turbulence below the proton gyroscale (see, e.g., Gary et al 2012;Saito and Gary 2012;Boldyrev and Perez 2012;Mithaiwala et al 2012). Particle-in-cell simulations show that the anisotropic whistler turbulence heats the electrons in the parallel direction as predicted by the linear theory and that in the low β plasmas the magnetic wavenumber spectrum becomes strongly anisotropic with spectral index in the perpendicular direction close to -4 (see, e.g., Gary et al 2012;Saito and Gary 2012).…”

Section: Collisionless Heating Of Ions and Electrons By Magnetic Turbmentioning

confidence: 99%

Collisionless Shocks in Partly Ionized Plasma with Cosmic Rays: Microphysics of Non-thermal Components

Bykov

Malkov

Raymond

et al. 2013

Microphysics of Cosmic Plasmas

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In this review we discuss some observational aspects and theoretical models of astrophysical collisionless shocks in partly ionized plasma with the presence of nonthermal components. A specific feature of fast strong collisionless shocks is their ability to accelerate energetic particles that can modify the shock upstream flow and form the shock precursors. We discuss the effects of energetic particle acceleration and associated magnetic field amplification and decay in the extended shock precursors on the line and continuum multi-wavelength emission spectra of the shocks. Both Balmer-type and radiative astrophysical shocks are discussed in connection to supernova remnants interacting with partially neutral clouds. Quantitative models described in the review predict a number of observable line-like emission features that can be used to reveal the physical state of the matter in the shock precursors and the character of nonthermal processes in the shocks. Implications of recent progress of gamma-ray observations of supernova remnants in molecular clouds are highlighted.

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Spectrum of Kinetic-Alfvén Turbulence

Cited by 178 publications

References 36 publications

ON THE SPECTRAL HARDENING AT ≳300 keV IN SOLAR FLARES

ON THE SPECTRAL HARDENING AT ≳300 keV IN SOLAR FLARES

Density Fluctuations Upstream and Downstream of Interplanetary Shocks

Collisionless Shocks in Partly Ionized Plasma with Cosmic Rays: Microphysics of Non-thermal Components

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