Oblique Alfvén Instabilities Driven by Compensated Currents

Malovichko, P. P.; Voitenko, Yuriy; Keyser, Johan De

doi:10.1088/0004-637x/780/2/175

Cited by 16 publications

(9 citation statements)

References 17 publications

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“…Plasma beta in the solar corona loops is generally larger than the square root of the electron to portion mass ratio (Gary 2001). Thus, because of the plasma density and magnetic field gradients, Alfvén waves are transformed to KAWs with a finite spatial scale across the magnetic field (Voitenko 1998;Zhao et al 2011;Malovichko et al 2014). The parallel electric field generated by KAWs (Hasegawa & Maclennan 1990) effectively traps electrons and transport them to the footpoints.…”

Section: System Geometry and Main Equationsmentioning

confidence: 99%

“…fast magnetosonic) wave modes can be effectively generated in solar loops by ion flows accelerated in the X-line. For example, ion flows excite kinetic Alfvén waves (KAWs) in the solar corona efficiently (Voitenko 1998;Zhao et al 2011;Malovichko et al 2014) with power-law spectrum and amplitudes of up to 0.1 V/m (Bian et al 2010). (Moreover, Chen et al 2014, show that electron beams can also generate KAWs in the flare loop plasma.)…”

Section: Introductionmentioning

confidence: 99%

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Electron trapping and acceleration by kinetic Alfvén waves in solar flares

Artemyev

Zimovets

Rankin

2016

A&A

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Context. Theoretical models and spacecraft observations of solar flares highlight the role of wave-particle interaction for non-local electron acceleration. In one scenario, the acceleration of a large electron population up to high energies is due to the transport of electromagnetic energy from the loop-top region down to the footpoints, which is then followed by the energy being released in dense plasma in the lower atmosphere. Aims. We consider one particular mechanism of non-linear electron acceleration by kinetic Alfvén waves. Here, waves are generated by plasma flows in the energy release region near the loop top. We estimate the efficiency of this mechanism and the energies of accelerated electrons. Methods. We use analytical estimates and test-particle modelling to investigate the effects of electron trapping and acceleration by kinetic Alfvén waves in the inhomogeneous plasma of the solar corona. Results. We demonstrate that, for realistic wave amplitudes, electrons can be accelerated up to 10−1000 keV during their propagation along magnetic field lines. Here the electric field that is parallel to the direction of the background magnetic field is about 10 to 10 3 times the amplitude of the Dreicer electric field. The acceleration mechanism strongly depends on electron scattering which is due to collisions that only take place near the loop footpoints. Conclusions. The non-linear wave-particle interaction can play an important role in the generation of relativistic electrons within flare loops. Electron trapping and coherent acceleration by kinetic Alfvén waves represent the energy cascade from large-scale plasma flows that originate at the loop-top region down to the electron scale. The non-diffusive character of the non-linear electron acceleration may be responsible for the fast generation of high-energy particles.

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Section: System Geometry and Main Equationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Electron trapping and acceleration by kinetic Alfvén waves in solar flares

Artemyev

Zimovets

Rankin

2016

A&A

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“…Current-driven instabilities can lead to aperiodic small-scale turbulence (Winske & Leroy 1984), that include parallel (Bell 2004) and oblique modes (Malovichko et al 2014). In conditions typical for the cosmic-ray precursors of the forward shocks of young SNR, the instability may operate for only a few growth times (Niemiec et al 2008), unless the remnant expands into a high-density environment, in which case, however, one has to consider ion-neutral collisions, which can reduce the growth of the instability (Reville et al 2007).…”

Section: Small-scale Non-resonant Modesmentioning

confidence: 99%

Reacceleration of electrons in supernova remnants

Pohl

Wilhelm

Telezhinsky

2015

A&A

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Context. The radio spectra of many shell-type supernova remnants show deviations from those expected on theoretical grounds. Aims. In this paper we determine the effect of stochastic reacceleration on the spectra of electrons in the GeV band and at lower energies, and we investigate whether reacceleration can explain the observed variation in radio spectral indices. Methods. We explicitely calculated the momentum diffusion coefficient for 3 types of turbulence expected downstream of the forward shock: fast-mode waves, small-scale non-resonant modes, and large-scale modes arising from turbulent dynamo activity. After noting that low-energy particles are efficiently coupled to the quasi-thermal plasma, a simplified cosmic-ray transport equation can be formulated and is numerically solved. Results. Only fast-mode waves can provide momentum diffusion fast enough to significantly modify the spectra of particles. Using a synchrotron emissivity that accurately reflects a highly turbulent magnetic field, we calculated the radio spectral index and find that soft spectra with index α −0.6 can be maintained over more than 2 decades in radio frequency, even if the electrons experience reacceleration for only one acceleration time. A spectral hardening is possible but considerably more frequency-dependent. The spectral modification imposed by stochastic reacceleration downstream of the forward shock depends only weakly on the initial spectrum provided by, e.g., diffusive shock acceleration at the shock itself.

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“…[6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] However, magnetized plasmas often experience counterstreaming along the ambient magnetic field, modifying a plasma velocity distribution function to a counterstreaming bi-Maxwellian or a counterstreaming kappa distribution function. In this case, much less results are available, especially as the analytical studies of the phenomena [21][22][23][24][25][26][27][28][29][30] are concerned. Since there is not yet a complete picture of kinetic instabilities in plasmas with counterstreaming distribution functions, the present manuscript might make a certain contribution to this field of researches.…”

Section: Introductionmentioning

confidence: 99%

“…Some recent similar studies have considered either Maxwellian or bi-Maxwellian distributions only with one streaming component for each plasma species, 28,29 whereas many features come from the counterstreaming nature. Presence of counterstreams in bi-Maxwellian plasmas leads to completely new instability conditions, which might be of extreme interest for the observations of the solar wind temperature anisotropy.…”

Section: Introductionmentioning

confidence: 99%

Linear theory of low frequency magnetosonic instabilities in counterstreaming bi-Maxwellian plasmas

2015

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An effect of the bi-Maxwellian counterstreaming distribution function is analyzed with regard to the linear low frequency instabilities in magnetized homogeneous collisionless plasmas. New analytical marginal instability conditions for the firehose and the mirror modes have been obtained. Presence of counterstreams along the ambient magnetic field causes a huge effect on the instability conditions of those modes. The instability conditions very sensitively depend on the functional dependence of the counterstreaming parameter P. The theoretically predicted results might give a full potential explanation for the observed solar wind temperature anisotropy diagram in A-β∥ plane [S. D. Bale et al., Phys. Rev. Lett. 103, 211101 (2009)].

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Oblique Alfvén Instabilities Driven by Compensated Currents

Cited by 16 publications

References 17 publications

Electron trapping and acceleration by kinetic Alfvén waves in solar flares

Electron trapping and acceleration by kinetic Alfvén waves in solar flares

Reacceleration of electrons in supernova remnants

Linear theory of low frequency magnetosonic instabilities in counterstreaming bi-Maxwellian plasmas

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