Wave Generation and Heat Flux Suppression in Astrophysical Plasma Systems

Roberg-Clark, Gareth; Drake, J. F.; Swisdak, M.; Reynolds, C. S.

doi:10.3847/1538-4357/aae393

Cited by 42 publications

(34 citation statements)

References 71 publications

(87 reference statements)

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“…Panel (a) presents the electron heat flux q e normalized to the free streaming heat flux q 0 = 1.5n e T e (T e /m e ) 1/2 versus β c|| = 8πn c T ||c /B 2 0 . At any given β c|| the heat flux is clearly below a threshold given by q e /q 0 ∼ 1/β c|| , that is similar to the marginally stable values in literature (Gary et al 1999a;Pistinner & Eichler 1998;Roberg-Clark et al 2018a;Komarov et al 2018;Roberg-Clark et al 2018b). However, at a given q e /q 0 both stable and unstable VDFs are observed, indicating thereby that some other parameter controls the onset of the whistler wave generation.…”

Section: Discussionsupporting

confidence: 76%

Whistler Wave Generation by Halo Electrons in the Solar Wind

Tong

Vasko

Pulupa

et al. 2019

ApJL

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We present an analysis of simultaneous particle and field measurements from the ARTEMIS spacecraft which demonstrate that quasi-parallel whistler waves in the solar wind can be generated locally by a bulk flow of halo electrons (whistler heat flux instability). ARTEMIS observes quasi-parallel whistler waves in the frequency range ∼ 0.05 − 0.2f ce simultaneously with electron velocity distribution functions that are a combination of counter-streaming core and halo populations. A linear stability analysis shows that the plasma is stable when there are no whistler waves, and unstable in the presence of whistler waves. In the latter case, the stability analysis shows that the whistler wave growth time is from a few to ten seconds at frequencies and wavenumbers that match the observations. The observations clearly demonstrate that the temperature anisotropy of halo electrons crucially affects the heat flux instability onset: a slight anisotropy T /T ⊥ > 1 may quench the instability, while a slight anisotropy T /T ⊥ < 1 may significantly increase the growth rate. These results demonstrate that heat flux inhibition is strongly dependent on the microscopic plasma properties.

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Section: Discussionsupporting

confidence: 76%

Whistler Wave Generation by Halo Electrons in the Solar Wind

Tong

Vasko

Pulupa

et al. 2019

ApJL

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“…The observations support this hypothesis, showing evidences of enhanced electromagnetic fluctuations usually associated with the heat-flux instabilities Gary et al 1999;Pagel et al 2007;Bale et al 2013;Lacombe et al 2014). Numerical simulations confirm a potential role of these instabilities in the regulation of electron heat-flux in the solar wind (Vocks et al 2005;Saito & Gary 2007;Roberg-Clark et al 2018).…”

Section: Introductionsupporting

confidence: 57%

Quasi-linear approach of the whistler heat-flux instability in the solar wind

Shaaban

Lazar

Yoon

et al. 2019

Monthly Notices of the Royal Astronomical Society

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The hot beaming (or strahl) electrons responsible for the main electron heat-flux in the solar wind are believed to be self-regulated by the electromagnetic beaming instabilities, also known as the heat-flux instabilities. Here we report the first quasilinear theoretical approach of the whistler unstable branch able to characterize the long-term saturation of the instability as well as the relaxation of the electron velocity distributions. The instability saturation is not solely determined by the drift velocities, which undergo only a minor relaxation, but mainly from a concurrent interaction of electrons with whistlers that induces (opposite) temperature anisotropies of the core and beam populations and reduces the effective anisotropy. These results might be able to (i) explain the low intensity of the whistler heat-flux fluctuations in the solar wind (although other explanations remain possible and need further investigation), and (ii) confirm a reduced effectiveness of these fluctuations in the relaxation and isotropization of the electron strahl and in the regulation of the electron heat-flux.

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“…Our simulation addresses the β ∼ 1 limit of flares. However, for a lower β simulation, whistler growth would be suppressed since less free energy would be available (Roberg-Clark et al 2018b). Scattering would still be expected to occur and the mode would retain a finite angle to B 0 .…”

Section: Discussionmentioning

confidence: 99%

Scattering of Energetic Electrons by Heat-flux-driven Whistlers in Flares

Roberg-Clark

Agapitov

Drake

et al. 2019

ApJ

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The scattering of electrons by heat-flux-driven whistler waves is explored with a particle-in-cell (PIC) simulation relevant to the transport of energetic electrons in flares. The simulation is initiated with a large heat flux that is produced using a kappa distribution of electrons with positive velocity and a cold return current beam. This system represents energetic electrons escaping from a reconnection-driven energy release site. This heat flux system drives large amplitude oblique whistler waves propagating both along and against the heat flux, as well as electron acoustic waves. While the waves are dominantly driven by the low energy electrons, including the cold return current beam, the energetic electrons resonate with and are scattered by the whistlers on time scales of the order of a hundred electron cyclotron times. Peak whistler amplitudes of B/B 0 ∼ 0.125 and angles of ∼ 60 • with respect to the background magnetic field are observed. Electron perpendicular energy is increased while the field-aligned electron heat flux is suppressed. The resulting scattering mean-free-paths of energetic electrons are small compared with the typical scale size of energy release sites in flares, which might lead to the effective confinement of energetic electrons that is required for the production of very energetic particles.

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Wave Generation and Heat Flux Suppression in Astrophysical Plasma Systems

Cited by 42 publications

References 71 publications

Whistler Wave Generation by Halo Electrons in the Solar Wind

Whistler Wave Generation by Halo Electrons in the Solar Wind

Quasi-linear approach of the whistler heat-flux instability in the solar wind

Scattering of Energetic Electrons by Heat-flux-driven Whistlers in Flares

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