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Eduard P Kontar - One of the best experts on this subject based on the ideXlab platform.
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The spectral difference between solar flare HXR coronal and footpoint sources due to wave-Particle Interactions
Astronomy and Astrophysics, 2011Co-Authors: Iain G. Hannah, Eduard P KontarAbstract:Aims. Investigate the spatial and spectral evolution of hard X-ra y (HXR) emission from flare accelerated electron beams subje ct to collisional transport and wave-Particle Interactions in t he solar atmosphere. Methods. We numerically follow the propagation of a power-law of accelerated electrons in 1D space and time with the response of the background plasma in the form of Langmuir waves using the quasilinear approximation. Results. We find that the addition of wave-Particle Interactions to co llisional transport for a transient initially injected ele ctron beam flattens the spectrum of the footpoint source. The coronal so urce is unchanged and so the difference in the spectral indices between the coronal and footpoint sources is � >2, which is larger than expected from purely collisional tra nsport. A steady-state beam shows little difference between the two cases, as has been previously found, as a transiently injected electron beam is required to produce significant wave growth, especially at higher veloc ities. With this transiently injected beam the wave-partic le Interactions dominate in the corona whereas the collisional losses dominate in the chromosphere. The shape of the spectrum is different with increasing electron beam density in the wave-Particle interaction case whereas with purely collisional transport onl y the normalisation is changed. We also find that the starting height of the source electron beam above the photosphere affects the spectral index of the footpoint when Langmuir wave growth is included. This may account for the differing spectral indices found between double footpoints if asymmetrical injection has occurred in the fla ring loop.
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The Effect of Wave-Particle Interactions on Low-Energy Cutoffs in Solar Flare Electron Spectra
The Astrophysical Journal, 2009Co-Authors: Iain G. Hannah, Eduard P Kontar, O. K. SirenkoAbstract:Solar flare hard X-ray (HXR) spectra from Reuven Ramaty High Energy Solar Spectrometer (RHESSI) are normally interpreted in terms of purely collisional electron beam propagation, ignoring spatial evolution and collective effects. In this Letter, we present self-consistent numerical simulations of the spatial and temporal evolution of an electron beam subject to collisional transport and beam-driven Langmuir wave turbulence. These wave-Particle Interactions represent the background plasma's response to the electron beam propagating from the corona to chromosphere and occur on a far faster timescale than Coulomb collisions. From these simulations, we derive the mean electron flux spectrum, comparable to such spectra recovered from high-resolution HXRs observations of solar flares with RHESSI. We find that a negative spectral index (i.e., a spectrum that increases with energy), or local minima when including the expected thermal spectral component at low energies, occurs in the standard thick-target model, when Coulomb collisions are only considered. The inclusion of wave-Particle Interactions does not produce a local minimum, maintaining a positive spectral index. These simulations are a step toward a more complete treatment of electron transport in solar flares and suggest that a flat spectrum (spectral index of 0-1) down to thermal energies maybe a better approximation instead of a sharp cutoff in the injected electron spectrum.
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The Effect of Wave-Particle Interactions on Low-Energy Cutoffs in Solar Flare Electron Spectra
The Astrophysical Journal, 2009Co-Authors: Iain G. Hannah, Eduard P Kontar, O. K. SirenkoAbstract:Solar flare hard X-ray (HXR) spectra from Reuven Ramaty High Energy Solar Spectrometer (RHESSI) are normally interpreted in terms of purely collisional electron beam propagation, ignoring spatial evolution and collective effects. In this Letter, we present self-consistent numerical simulations of the spatial and temporal evolution of an electron beam subject to collisional transport and beam-driven Langmuir wave turbulence. These wave-Particle Interactions represent the background plasma's response to the electron beam propagating from the corona to chromosphere and occur on a far faster timescale than Coulomb collisions. From these simulations, we derive the mean electron flux spectrum, comparable to such spectra recovered from high-resolution HXRs observations of solar flares with RHESSI. We find that a negative spectral index (i.e., a spectrum that increases with energy), or local minima when including the expected thermal spectral component at low energies, occurs in the standard thick-target model, when Coulomb collisions are only considered. The inclusion of wave-Particle Interactions does not produce a local minimum, maintaining a positive spectral index. These simulations are a step toward a more complete treatment of electron transport in solar flares and suggest that a flat spectrum (spectral index of 0-1) down to thermal energies maybe a better approximation instead of a sharp cutoff in the injected electron spectrum.
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the effect of wave Particle Interactions on low energy cutoffs in solar flare electron spectra
arXiv: Solar and Stellar Astrophysics, 2009Co-Authors: Iain G. Hannah, Eduard P Kontar, O. K. SirenkoAbstract:Solar flare hard X-ray spectra from RHESSI are normally interpreted in terms of purely collisional electron beam propagation, ignoring spatial evolution and collective effects. In this paper we present self-consistent numerical simulations of the spatial and temporal evolution of an electron beam subject to collisional transport and beam-driven Langmuir wave turbulence. These wave-Particle Interactions represent the background plasma's response to the electron beam propagating from the corona to chromosphere and occur on a far faster timescale than coulomb collisions. From these simulations we derive the mean electron flux spectrum, comparable to such spectra recovered from high resolution hard X-rays observations of solar flares with RHESSI. We find that a negative spectral index (i.e. a spectrum that increases with energy), or local minima when including the expected thermal spectral component at low energies, occurs in the standard thick-target model, when coulomb collisions are only considered. The inclusion of wave-Particle Interactions does not produce a local minimum, maintaining a positive spectral index. These simulations are a step towards a more complete treatment of electron transport in solar flares and suggest that a flat spectrum (spectral index of 0 to 1) down to thermal energies maybe a better approximation instead of a sharp cut-off in the injected electron spectrum.
Iain G. Hannah - One of the best experts on this subject based on the ideXlab platform.
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The spectral difference between solar flare HXR coronal and footpoint sources due to wave-Particle Interactions
Astronomy and Astrophysics, 2011Co-Authors: Iain G. Hannah, Eduard P KontarAbstract:Aims. Investigate the spatial and spectral evolution of hard X-ra y (HXR) emission from flare accelerated electron beams subje ct to collisional transport and wave-Particle Interactions in t he solar atmosphere. Methods. We numerically follow the propagation of a power-law of accelerated electrons in 1D space and time with the response of the background plasma in the form of Langmuir waves using the quasilinear approximation. Results. We find that the addition of wave-Particle Interactions to co llisional transport for a transient initially injected ele ctron beam flattens the spectrum of the footpoint source. The coronal so urce is unchanged and so the difference in the spectral indices between the coronal and footpoint sources is � >2, which is larger than expected from purely collisional tra nsport. A steady-state beam shows little difference between the two cases, as has been previously found, as a transiently injected electron beam is required to produce significant wave growth, especially at higher veloc ities. With this transiently injected beam the wave-partic le Interactions dominate in the corona whereas the collisional losses dominate in the chromosphere. The shape of the spectrum is different with increasing electron beam density in the wave-Particle interaction case whereas with purely collisional transport onl y the normalisation is changed. We also find that the starting height of the source electron beam above the photosphere affects the spectral index of the footpoint when Langmuir wave growth is included. This may account for the differing spectral indices found between double footpoints if asymmetrical injection has occurred in the fla ring loop.
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The Effect of Wave-Particle Interactions on Low-Energy Cutoffs in Solar Flare Electron Spectra
The Astrophysical Journal, 2009Co-Authors: Iain G. Hannah, Eduard P Kontar, O. K. SirenkoAbstract:Solar flare hard X-ray (HXR) spectra from Reuven Ramaty High Energy Solar Spectrometer (RHESSI) are normally interpreted in terms of purely collisional electron beam propagation, ignoring spatial evolution and collective effects. In this Letter, we present self-consistent numerical simulations of the spatial and temporal evolution of an electron beam subject to collisional transport and beam-driven Langmuir wave turbulence. These wave-Particle Interactions represent the background plasma's response to the electron beam propagating from the corona to chromosphere and occur on a far faster timescale than Coulomb collisions. From these simulations, we derive the mean electron flux spectrum, comparable to such spectra recovered from high-resolution HXRs observations of solar flares with RHESSI. We find that a negative spectral index (i.e., a spectrum that increases with energy), or local minima when including the expected thermal spectral component at low energies, occurs in the standard thick-target model, when Coulomb collisions are only considered. The inclusion of wave-Particle Interactions does not produce a local minimum, maintaining a positive spectral index. These simulations are a step toward a more complete treatment of electron transport in solar flares and suggest that a flat spectrum (spectral index of 0-1) down to thermal energies maybe a better approximation instead of a sharp cutoff in the injected electron spectrum.
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The Effect of Wave-Particle Interactions on Low-Energy Cutoffs in Solar Flare Electron Spectra
The Astrophysical Journal, 2009Co-Authors: Iain G. Hannah, Eduard P Kontar, O. K. SirenkoAbstract:Solar flare hard X-ray (HXR) spectra from Reuven Ramaty High Energy Solar Spectrometer (RHESSI) are normally interpreted in terms of purely collisional electron beam propagation, ignoring spatial evolution and collective effects. In this Letter, we present self-consistent numerical simulations of the spatial and temporal evolution of an electron beam subject to collisional transport and beam-driven Langmuir wave turbulence. These wave-Particle Interactions represent the background plasma's response to the electron beam propagating from the corona to chromosphere and occur on a far faster timescale than Coulomb collisions. From these simulations, we derive the mean electron flux spectrum, comparable to such spectra recovered from high-resolution HXRs observations of solar flares with RHESSI. We find that a negative spectral index (i.e., a spectrum that increases with energy), or local minima when including the expected thermal spectral component at low energies, occurs in the standard thick-target model, when Coulomb collisions are only considered. The inclusion of wave-Particle Interactions does not produce a local minimum, maintaining a positive spectral index. These simulations are a step toward a more complete treatment of electron transport in solar flares and suggest that a flat spectrum (spectral index of 0-1) down to thermal energies maybe a better approximation instead of a sharp cutoff in the injected electron spectrum.
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the effect of wave Particle Interactions on low energy cutoffs in solar flare electron spectra
arXiv: Solar and Stellar Astrophysics, 2009Co-Authors: Iain G. Hannah, Eduard P Kontar, O. K. SirenkoAbstract:Solar flare hard X-ray spectra from RHESSI are normally interpreted in terms of purely collisional electron beam propagation, ignoring spatial evolution and collective effects. In this paper we present self-consistent numerical simulations of the spatial and temporal evolution of an electron beam subject to collisional transport and beam-driven Langmuir wave turbulence. These wave-Particle Interactions represent the background plasma's response to the electron beam propagating from the corona to chromosphere and occur on a far faster timescale than coulomb collisions. From these simulations we derive the mean electron flux spectrum, comparable to such spectra recovered from high resolution hard X-rays observations of solar flares with RHESSI. We find that a negative spectral index (i.e. a spectrum that increases with energy), or local minima when including the expected thermal spectral component at low energies, occurs in the standard thick-target model, when coulomb collisions are only considered. The inclusion of wave-Particle Interactions does not produce a local minimum, maintaining a positive spectral index. These simulations are a step towards a more complete treatment of electron transport in solar flares and suggest that a flat spectrum (spectral index of 0 to 1) down to thermal energies maybe a better approximation instead of a sharp cut-off in the injected electron spectrum.
Nigel P. Meredith - One of the best experts on this subject based on the ideXlab platform.
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Wave-Particle Interactions in the equatorial source region of whistler-mode emissions
Journal of Geophysical Research, 2010Co-Authors: Ondřej Santolík, S. Grimald, Michel Parrot, Nicole Cornilleau-wehrlin, F. El-lemdani Mazouz, David Schriver, Jolene S. Pickett, P M E Decreau, Nigel P. MeredithAbstract:[1] Wave-Particle Interactions can play a key role in the process of transfer of energy between different electron populations in the outer Van Allen radiation belt. We present a case study of wave-Particle Interactions in the equatorial source region of whistler-mode emissions. We select measurements of the Cluster spacecraft when these emissions are observed in the form of random hiss with only occasional discrete chorus wave packets, and where the wave propagation properties are very similar to previously analyzed cases of whistler-mode chorus. We observe a positive divergence of the Poynting flux at minima of the magnetic field modulus along the magnetic field lines, indicating the central position of the source. In this region we perform a linear stability analysis based on the locally measured electron phase space densities. We find two unstable electron populations. The first of them consists of energy-dispersed and highly anisotropic injected electrons at energies of a few hundreds eV to a few keV, with the perpendicular temperature more than 10 times higher than the parallel temperature with respect to the magnetic field line. Another unstable population is formed by trapped electrons at energies above 10 keV. We show that the injected electrons at lower energies can be responsible for a part of the waves that propagate obliquely at frequencies above one half of the electron cyclotron frequency. Our model of the trapped electrons at higher energies gives insufficient growth of the waves below one half of the electron cyclotron frequency and a nonlinear generation mechanism might be necessary to explain their presence even in this simple case.
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Wave‐Particle Interactions in the equatorial source region of whistler‐mode emissions
Journal of Geophysical Research, 2010Co-Authors: Ondřej Santolík, S. Grimald, Michel Parrot, Nicole Cornilleau-wehrlin, F. El-lemdani Mazouz, David Schriver, Jolene S. Pickett, P M E Decreau, Nigel P. MeredithAbstract:[1] Wave-Particle Interactions can play a key role in the process of transfer of energy between different electron populations in the outer Van Allen radiation belt. We present a case study of wave-Particle Interactions in the equatorial source region of whistler-mode emissions. We select measurements of the Cluster spacecraft when these emissions are observed in the form of random hiss with only occasional discrete chorus wave packets, and where the wave propagation properties are very similar to previously analyzed cases of whistler-mode chorus. We observe a positive divergence of the Poynting flux at minima of the magnetic field modulus along the magnetic field lines, indicating the central position of the source. In this region we perform a linear stability analysis based on the locally measured electron phase space densities. We find two unstable electron populations. The first of them consists of energy-dispersed and highly anisotropic injected electrons at energies of a few hundreds eV to a few keV, with the perpendicular temperature more than 10 times higher than the parallel temperature with respect to the magnetic field line. Another unstable population is formed by trapped electrons at energies above 10 keV. We show that the injected electrons at lower energies can be responsible for a part of the waves that propagate obliquely at frequencies above one half of the electron cyclotron frequency. Our model of the trapped electrons at higher energies gives insufficient growth of the waves below one half of the electron cyclotron frequency and a nonlinear generation mechanism might be necessary to explain their presence even in this simple case.
O. K. Sirenko - One of the best experts on this subject based on the ideXlab platform.
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The Effect of Wave-Particle Interactions on Low-Energy Cutoffs in Solar Flare Electron Spectra
The Astrophysical Journal, 2009Co-Authors: Iain G. Hannah, Eduard P Kontar, O. K. SirenkoAbstract:Solar flare hard X-ray (HXR) spectra from Reuven Ramaty High Energy Solar Spectrometer (RHESSI) are normally interpreted in terms of purely collisional electron beam propagation, ignoring spatial evolution and collective effects. In this Letter, we present self-consistent numerical simulations of the spatial and temporal evolution of an electron beam subject to collisional transport and beam-driven Langmuir wave turbulence. These wave-Particle Interactions represent the background plasma's response to the electron beam propagating from the corona to chromosphere and occur on a far faster timescale than Coulomb collisions. From these simulations, we derive the mean electron flux spectrum, comparable to such spectra recovered from high-resolution HXRs observations of solar flares with RHESSI. We find that a negative spectral index (i.e., a spectrum that increases with energy), or local minima when including the expected thermal spectral component at low energies, occurs in the standard thick-target model, when Coulomb collisions are only considered. The inclusion of wave-Particle Interactions does not produce a local minimum, maintaining a positive spectral index. These simulations are a step toward a more complete treatment of electron transport in solar flares and suggest that a flat spectrum (spectral index of 0-1) down to thermal energies maybe a better approximation instead of a sharp cutoff in the injected electron spectrum.
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The Effect of Wave-Particle Interactions on Low-Energy Cutoffs in Solar Flare Electron Spectra
The Astrophysical Journal, 2009Co-Authors: Iain G. Hannah, Eduard P Kontar, O. K. SirenkoAbstract:Solar flare hard X-ray (HXR) spectra from Reuven Ramaty High Energy Solar Spectrometer (RHESSI) are normally interpreted in terms of purely collisional electron beam propagation, ignoring spatial evolution and collective effects. In this Letter, we present self-consistent numerical simulations of the spatial and temporal evolution of an electron beam subject to collisional transport and beam-driven Langmuir wave turbulence. These wave-Particle Interactions represent the background plasma's response to the electron beam propagating from the corona to chromosphere and occur on a far faster timescale than Coulomb collisions. From these simulations, we derive the mean electron flux spectrum, comparable to such spectra recovered from high-resolution HXRs observations of solar flares with RHESSI. We find that a negative spectral index (i.e., a spectrum that increases with energy), or local minima when including the expected thermal spectral component at low energies, occurs in the standard thick-target model, when Coulomb collisions are only considered. The inclusion of wave-Particle Interactions does not produce a local minimum, maintaining a positive spectral index. These simulations are a step toward a more complete treatment of electron transport in solar flares and suggest that a flat spectrum (spectral index of 0-1) down to thermal energies maybe a better approximation instead of a sharp cutoff in the injected electron spectrum.
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the effect of wave Particle Interactions on low energy cutoffs in solar flare electron spectra
arXiv: Solar and Stellar Astrophysics, 2009Co-Authors: Iain G. Hannah, Eduard P Kontar, O. K. SirenkoAbstract:Solar flare hard X-ray spectra from RHESSI are normally interpreted in terms of purely collisional electron beam propagation, ignoring spatial evolution and collective effects. In this paper we present self-consistent numerical simulations of the spatial and temporal evolution of an electron beam subject to collisional transport and beam-driven Langmuir wave turbulence. These wave-Particle Interactions represent the background plasma's response to the electron beam propagating from the corona to chromosphere and occur on a far faster timescale than coulomb collisions. From these simulations we derive the mean electron flux spectrum, comparable to such spectra recovered from high resolution hard X-rays observations of solar flares with RHESSI. We find that a negative spectral index (i.e. a spectrum that increases with energy), or local minima when including the expected thermal spectral component at low energies, occurs in the standard thick-target model, when coulomb collisions are only considered. The inclusion of wave-Particle Interactions does not produce a local minimum, maintaining a positive spectral index. These simulations are a step towards a more complete treatment of electron transport in solar flares and suggest that a flat spectrum (spectral index of 0 to 1) down to thermal energies maybe a better approximation instead of a sharp cut-off in the injected electron spectrum.
A. Dengra - One of the best experts on this subject based on the ideXlab platform.
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Surface-wave–Particle Interactions in a cylindrical plasma submitted to a static magnetic field
Physics of Plasmas, 1997Co-Authors: A. DengraAbstract:A new theoretical model for the study of the surface-wave–Particle Interactions in a plasma column in the presence of a constant external magnetic field has been developed. The model is based on the linear resolution of the Vlasov equation by the method of characteristics, with the specular reflection hypothesis at the wall. The expression obtained for the rate of increase of kinetic energy per electron permits the analysis of the influence of the critical parameters in this transference process.
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Nonlinear theory of surface-wave-Particle Interactions in a cylindrical plasma.
Physical Review E, 1994Co-Authors: A. Dengra, J. I. F. PalopAbstract:This work is an application of the specular reflection hypothesis to the study of the nonlinear surface-wave--Particle Interactions in a cylindrical plasma. The model is based on nonlinear resolution of the Vlasov equation by the method of characteristics. The expression obtained for the rate of increase of kinetic energy per electron has permitted us to investigate the temporal behavior of nonlinear collisionless damping for different situations as a function of the critical parameters.
