Turbulent anomalous transport and anisotropic electron heating in a return current system

Lee, Kuang Wu; Büchner, Jörg

doi:10.1063/1.3553026

Cited by 4 publications

(10 citation statements)

References 22 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Hence, in the course of beam propagation the original isotropic drifting Maxwellian distributions of electron beams evolve into anisotropic ones. Anisotropic electron heating has already been reported in Lee & Büchner (2011b), who considered the case without a background magnetic field B x . By comparing the simulation results, one notices that the perpendicular electron heatings are stronger in the unmagnetized case (Lee & Büchner 2011b), which are T y,e1 = 4.99 keV and T y,e2 = 3.74 keV at the end of simulation.…”

Section: Collisionless Momentum Transport By Electromagnetic Turbulencesmentioning

confidence: 90%

“…(2)) can be found in Lee & Büchner (2011b). In the above equation the term T α,|| −T α,⊥ is the temperature difference between parallel and perpendicular directions.…”

Section: Energy Conversion and Electron Heatingmentioning

confidence: 99%

“…Anisotropic electron heating caused by electron turbulent deflections in an unmagnetized plasma has been discussed in Lee & Büchner (2011b). For the anisotropic electron heating in magnetized plasma we examined the localized turbulence and the intensity of electron perpendicular flow.…”

Section: Energy Conversion and Electron Heatingmentioning

confidence: 99%

“…, compared to the maximum perpendicular momentum of unmagnetized plasma (see Fig. 7 in Lee & Büchner 2011b).…”

Section: Energy Conversion and Electron Heatingmentioning

confidence: 99%

“…(2.20) in or Eq. (8) in Lee & Büchner (2011b), can be used for the investigation of eigen modes and instabilities. We calculated the multi-fluid dispersion relation with the applied plasma parameters.…”

Section: Model Setup and Multifluid Dispersion Analysismentioning

confidence: 99%

See 4 more Smart Citations

Collisionless turbulent transport and anisotropic electron heating in coronal flare loops

Lee¹,

Büchner²

2011

A&A

View full text Add to dashboard Cite

Context. One of the hypotheses about the generation of the hard X-ray emissions (HXR) of the sun is that a strong electron-beam is first accelerated near the looptop, and then propagated down to the chromosphere. There the HXR emissions are generated by the bombardment of electrons via thick-target bremsstrahlung. Recently, the beam-plasma model has been questioned because streaming instabilities make the beam propagation doubtful. Another open question in solar flare models is the generation of anisotropic electron distributions deduced from microwave emissions. The question is whether one can find a mechanism, in addition to the generally considered mirror motion, that may cause the electron anisotropy in flare loops. Aims. To understand the transport of coronal electron beams and the possible generation of electron anisotropic distribution in the course of the beam propagation, we simulated a beam-plasma return-current system. Our aim is to investigate the evolution of predicted streaming instabilities at the nonlinear stage and to determine the intensity of beam transport in coronal loops. Methods. The linear instabilities and wave coupling in the beam-plasma return-current system are investigated by a multi-fluid dispersion analysis. We performed a two-dimensional electromagnetic particle-in-cell simulation to understand the generation of turbulent transport and anisotropic electron heating at the nonlinear stage of the beam evolution. Results. The beam-plasma return-current system is stablized at a late stage of evolution by a combined effect of 1) a relaxation of electron bulk drifts; and 2) a fast thermalization of the beam and return-current electrons in the drift direction. As a result, the downward electron beam continues to propagate in the coronal loop. Distinguishable parallel and perpendicular electron heating is observed, which is caused by turbulent deflection of electron beams. The electron distribution becomes anisotropic through different heating rates.Conclusions. An electron beam injected from a solar flare looptop can continue to propagate stably despite a partial relaxation of its drift velocity. After drift relaxation and anisotropic electron heating, the slowed-down electron drifts and the ambient thermalized plasma create a stable beam-propagation environment because of the Landau damping effect. This electron beam can propagate stably at a modified drift speed down to the chromosphere, where it generates HXR radiation. We conclude that the beam plasma model is feasible for the HXR generation in a solar flare event. The observed anisotropic electron distribution is a direct consequence of turbulent deflections of the electron beams.

show abstract

Section: Collisionless Momentum Transport By Electromagnetic Turbulencesmentioning

confidence: 90%

“…(2)) can be found in Lee & Büchner (2011b). In the above equation the term T α,|| −T α,⊥ is the temperature difference between parallel and perpendicular directions.…”

Section: Energy Conversion and Electron Heatingmentioning

confidence: 99%

Section: Energy Conversion and Electron Heatingmentioning

confidence: 99%

“…, compared to the maximum perpendicular momentum of unmagnetized plasma (see Fig. 7 in Lee & Büchner 2011b).…”

Section: Energy Conversion and Electron Heatingmentioning

confidence: 99%

Section: Model Setup and Multifluid Dispersion Analysismentioning

confidence: 99%

See 3 more Smart Citations

Collisionless turbulent transport and anisotropic electron heating in coronal flare loops

Lee¹,

Büchner²

2011

A&A

View full text Add to dashboard Cite

show abstract

Wave Emission of Nonthermal Electron Beams Generated by Magnetic Reconnection

Yao

Muñoz²,

Büchner³

et al. 2022

ApJ

Self Cite

View full text Add to dashboard Cite

Magnetic reconnection in solar flares can efficiently generate nonthermal electron beams. The energetic electrons can, in turn, cause radio waves through microscopic plasma instabilities as they propagate through the ambient plasma along the magnetic field lines. We aim at investigating the wave emission caused by fast-moving electron beams with characteristic nonthermal electron velocity distribution functions (EVDFs) generated by kinetic magnetic reconnection: two-stream EVDFs along the separatrices and in the diffusion region, and perpendicular crescent-shaped EVDFs closer to the diffusion region. For this purpose, we utilized 2.5D fully kinetic Particle-In-Cell code simulations in this study. We found the following: (1) the two-stream EVDFs plus the background ions are unstable to electron/ion (streaming) instabilities, which cause ion-acoustic waves and Langmuir waves due to the net current. This can lead to multiple-harmonic plasma emission in the diffusion region and the separatrices of reconnection. (2) The perpendicular crescent-shaped EVDFs can cause multiple-harmonic electromagnetic electron cyclotron waves through the electron cyclotron maser instabilities in the diffusion region of reconnection. Our results are applicable to diagnose the plasma parameters, which are associated to magnetic reconnection in solar flares by means of radio wave observations.

show abstract

The Impulsive Phase in Solar Flares: Recent Multi-wavelength Results and their Implications for Microwave Modeling and Observations

Fletcher¹,

Simões²

2013

Preprint

View full text Add to dashboard Cite

This short paper reviews several recent key observations of the processes occurring in the lower atmosphere (chromosphere and photosphere) during flares. These are: evidence for compact and fragmentary structure in the flare chromosphere, the conditions in optical flare footpoints, step-like variations in the magnetic field during the flare impulsive phase, and hot, dense 'chromospheric' footpoints. The implications of these observations for microwaves are also discussed.

show abstract

Turbulent anomalous transport and anisotropic electron heating in a return current system

Cited by 4 publications

References 22 publications

Collisionless turbulent transport and anisotropic electron heating in coronal flare loops

Collisionless turbulent transport and anisotropic electron heating in coronal flare loops

Wave Emission of Nonthermal Electron Beams Generated by Magnetic Reconnection

The Impulsive Phase in Solar Flares: Recent Multi-wavelength Results and their Implications for Microwave Modeling and Observations

Contact Info

Product

Resources

About