An analytical description of a stationary triple vortex, observed in a cylindrical plasma, is pre... more An analytical description of a stationary triple vortex, observed in a cylindrical plasma, is presented. The concentration of neutrals, which is rather high in the experiment, turns out to be of crucial importance due to a spatially dependent distribution. In the radial direction the neutral concentration is paraboliclike, yielding an effective radial force directed towards the axis of the system. This neutral force causes the rotation of the plasma in the direction which is opposite to theẼ E B B drift. The stationary triple vortex develops for a starting Gaussian-density distribution and a rigid-body rotation of the plasma column.
Simulation results of three-dimensional (3D) stationary magnetohydrodynamic (MHD) bow-shock flows... more Simulation results of three-dimensional (3D) stationary magnetohydrodynamic (MHD) bow-shock flows around perfectly conducting spheres are presented. For strong upstream magnetic field a new complex bow-shock flow topology arises consisting of two consecutive interacting shock fronts. It is shown that the leading shock front contains a segment of intermediate 1-3 shock type. This is the first confirmation in 3D that intermediate shocks, which were believed to be unphysical for a long time, can be formed and can persist for small-dissipation MHD in a realistic flow configuration.
The propagation of compressional MHD waves is studied for an externally driven system. It is assu... more The propagation of compressional MHD waves is studied for an externally driven system. It is assumed that the combined action of the external sources and sinks of the entropy results in the harmonic oscillation of the entropy (and temperature) in the system. It is found that with the appropriate resonant conditions fast and slow waves get amplified due to the phenomenon of parametric resonance. Besides, it is shown that the considered waves are mutually coupled as a consequence of the nonequilibrium state of the background medium. The coupling is strongest when the plasma β ≈ 1. The proposed formalism is sufficiently general and can be applied for many dynamical systems, both under terrestrial and astrophysical conditions.
A purely kinetic instability of the dust acoustic mode in inhomogeneous plasmas is discussed. In ... more A purely kinetic instability of the dust acoustic mode in inhomogeneous plasmas is discussed. In the presence of a magnetic field, electrons and ions may be magnetized while at the same time dust grains may remain unmagnetized. Although the dynamics of the light species is strongly affected by the magnetic field, the dust acoustic mode may still propagate in practically any direction. The inhomogeneity implies a source of free energy for an instability that develops through the diamagnetic drift effects of the magnetized species. It is shown that this may be a powerful mechanism for the excitation of dust acoustic waves. The analysis presented in the work is also directly applicable to plasmas containing both positive and negative ions and electrons, provided that at least one of the two ion species is unmagnetized.
It is shown that nonlinear three-wave interaction, described by vector-product type nonlinearitie... more It is shown that nonlinear three-wave interaction, described by vector-product type nonlinearities, in pair plasmas implies much more restrictive conditions for a double energy transfer, as compared to electron-ion plasmas. PACS numbers: 52.35.Mw, 52.30.Ex, 52.27.Ep a) [email protected] b) [email protected]
An analysis of the temperature-gradient-driven ͑ i ͒ instability of drift waves in dusty plasma i... more An analysis of the temperature-gradient-driven ͑ i ͒ instability of drift waves in dusty plasma is presented. Various limits that allow for the coupling of the drift wave with the dynamics of dust grains are discussed. In particular, the cases of tiny (magnetized) and relatively heavy (unmagnetized) grains are studied. It is shown that in both limits the behavior of the i mode is considerably affected by the dust dynamics. The growth rate turns out to be higher in the presence of dust, and the instability threshold is lower, resulting in a more unstable plasma.
Response of nonuniform magnetized plasma to strongly nonlinear electromagnetic perturbations driv... more Response of nonuniform magnetized plasma to strongly nonlinear electromagnetic perturbations driven by nonuniform £ows is studied.Various types of coherent structures with spatial scales of the order of the electron skin depth are found carried by the £ow or propagating through the plasma, with spatial scales measured in tens of kilometers for the magnetotail region.
Monthly Notices of the Royal Astronomical Society, 2009
The heating of the plasma in the solar atmosphere is discussed within both frameworks of fluid an... more The heating of the plasma in the solar atmosphere is discussed within both frameworks of fluid and kinetic drift wave theory. We show that the basic ingredient necessary for the heating is the presence of density gradients in the direction perpendicular to the magnetic field vector. Such density gradients are a source of free energy for the excitation of drift waves. We use only well established basic theory, verified experimentally in laboratory plasmas. Two mechanisms of the energy exchange and heating are shown to take place simultaneously: one due to the Landau effect in the direction parallel to the magnetic field, and another one, stochastic heating, in the perpendicular direction. The stochastic heating i) is due to the electrostatic nature of the waves, ii) is more effective on ions than on electrons, iii) acts predominantly in the perpendicular direction, iv) heats heavy ions more efficiently than lighter ions, and v) may easily provide a drift wave heating rate that is orders of magnitude above the value that is presently believed to be sufficient for the coronal heating, i.e., ≃ 6 · 10 −5 J/(m 3 s) for active regions and ≃ 8 · 10 −6 J/(m 3 s) for coronal holes. This heating acts naturally through well known effects that are, however, beyond the current standard models and theories.
Monthly Notices of the Royal Astronomical Society, 2014
We investigate electrostatic plasma instabilities of Farley-Buneman (FB) type driven by quasistat... more We investigate electrostatic plasma instabilities of Farley-Buneman (FB) type driven by quasistationary neutral gas flows in the solar chromosphere. The role of these instabilities in the chromosphere is clarified. We find that the destabilizing ion thermal effect is highly reduced by the Coulomb collisions and can be ignored for the chromospheric FB-type instabilities. In contrast, the destabilizing electron thermal effect is important and causes a significant reduction of the neutral drag velocity triggering the instability. The resulting threshold velocity is found as function of chromospheric height. Our results indicate that the FB-type instabilities are still less efficient in the global chromospheric heating than the Joule dissipation of the currents driving these instabilities. This conclusion does not exclude the possibility that the FB-type instabilities develop in the places where the cross-field currents overcome the threshold value and contribute to the heating locally. Typical length-scales of plasma density fluctuations produced by these instabilities are determined by the wavelengths of unstable modes, which are in the range 10-10 2 cm in the lower chromosphere and 10 2 -10 3 cm in the upper chromosphere. These results suggest that the decimetric radio waves undergoing scattering (scintillations) by these plasma irregularities can serve as a tool for remote probing of the solar chromosphere at different heights.
Monthly Notices of the Royal Astronomical Society, 2010
The efficiency of nonmodal self-heating by acoustic wave perturbations is examined. Considering d... more The efficiency of nonmodal self-heating by acoustic wave perturbations is examined. Considering different kinds of kinematically complex velocity patterns we show that nonmodal instabilities arising in these inhomogeneous flows may lead to significant amplification of acoustic waves. Subsequently, the presence of viscous dissipation damps these amplified waves and causes the energy transfer back to the background flow in the form of heat; viz. closes the "self-heating" cycle and contributes to the net heating of the flow patterns and the chromospheric network as a whole. The acoustic selfheating depends only on the presence of kinematically complex flows and dissipation. It is argued that together with other mechanisms of nonlinear nature the self-heating may be a probable additinal mechanism of nonmagnetic chromospheric heating in the Sun and other solar-type stars with slow rotation and extended convective regions.
Monthly Notices of the Royal Astronomical Society, 2010
Non-thermal particle distributions of kappa type are frequently encountered in collisionless plas... more Non-thermal particle distributions of kappa type are frequently encountered in collisionless plasmas from space. The electromagnetic emissions coming from space are believed to originate in the counterstreaming structures of plasmas, which are ubiquitous in many astrophysical systems. Here, we investigate the dispersion properties and the stability of a counterstreaming plasma system with temperature anisotropies modelled by a bi-kappa distribution function. The numerical evaluation of parallel modes shows growth rates lower than those obtained for Maxwellian plasmas, with a strong dependence on the spectral index of the particle distribution function. If all other parameters are known, measuring the instability growth time can provide a possible tool for the determination of the spectral index κ.
Monthly Notices of the Royal Astronomical Society, 2000
The electrostatic instabilities driven by the gradients of the density, temperature and magnetic ... more The electrostatic instabilities driven by the gradients of the density, temperature and magnetic field, are discussed in their application to solar magnetic structures. Strongly growing modes are found for some typical plasma parameters. These instabilities i) imply the presence of electric fields that can accelerate the plasma particles in both perpendicular and parallel directions with respect to the magnetic field vector, and ii) can stochastically heat ions. The perpendicular acceleration is to the leading order determined by the E × B-drift acting equally on both ions and electrons, while the parallel acceleration is most effective on electrons. The experimentally confirmed stochastic heating is shown to act mainly in the direction perpendicular to the magnetic field vector and acts stronger on heavier ions. The energy release rate and heating may exceed for several orders of magnitude the value accepted as necessary for a selfsustained heating in the solar corona. The energy source for both the acceleration and the heating is stored in the mentioned background gradients.
Monthly Notices of the Royal Astronomical Society, 2010
In the solar corona, several mechanisms of the drift wave instability can make the mode growing u... more In the solar corona, several mechanisms of the drift wave instability can make the mode growing up to amplitudes at which particle acceleration and stochastic heating by the drift wave take place. The stochastic heating, well known from laboratory plasma physics where it has been confirmed in numerous experiments, has been completely ignored in past studies of coronal heating. However, in the present study and in our very recent works it has been shown that the inhomogeneous coronal plasma is, in fact, a perfect environment for fast growing drift waves. As a matter of fact, the large growth rates are typically of the same order as the wave frequency. The consequent heating rates may exceed the required values for a sustained coronal heating by several orders of magnitude. Some aspects of these phenomena are investigated here. In particular the analysis of the particle dynamics within the growing wave is compared with the corresponding fluid analysis. While both of them predict the stochastic heating, the threshold for the heating obtained from the single particle analysis is higher. The explanation for this effect is given.
Monthly Notices of the Royal Astronomical Society, 2014
The electron cyclotron emissions represent a useful tool in the diagnostics of fusion plasmas and... more The electron cyclotron emissions represent a useful tool in the diagnostics of fusion plasmas and space plasma fluctuations. The instability which enhances the whistler-cyclotron modes is driven in the presence of an ambient regular magnetic field by an excess of transverse kinetic energy of plasma particles. Previous studies have modelled the anisotropic particles with a bi-Maxwellian or a bi-Kappa distribution function and found a suppression of this instability in the presence of suprathermal tails. Here, the anisotropic plasma is modelled with a product-bi-Kappa distribution, with the advantage that this distribution function enables the use of two different spectral indices in the main directions, κ = κ ⊥ , and permits further characterization of kappa populations and their excitations. The exact numerical values of the growth rates and the instability threshold are derived and contrasted with those for a simple bi-Kappa and a bi-Maxwellian, using plasma parameters and magnetic fields relevant for the solar and terrestrial environments.
In this study, we test the flux rope paradigm by performing a "blind" reconstruction of the magne... more In this study, we test the flux rope paradigm by performing a "blind" reconstruction of the magnetic field structure of a simulated interplanetary coronal mass ejection (ICME). The ICME is the result of a magneto-hydrodynamic (MHD) numerical simulation and does not exhibit much magnetic twist, but appears to have some characteristics of a magnetic cloud, due to a writhe in the magnetic field lines. We use the Grad-Shafranov technique with simulated spacecraft measurements at two different distances and compare the reconstructed magnetic field with that of the ICME in the simulation. While the reconstructed magnetic field is similar to the simulated one as seen in two dimensions, it yields a helically twisted magnetic field in three dimensions. To further verify the results, we perform the reconstruction at three different position angles at every distance point, and all results come into agreement. This work demonstrates that the current paradigm of associating magnetic clouds with flux ropes may have to be revised.
An analytical description of a stationary triple vortex, observed in a cylindrical plasma, is pre... more An analytical description of a stationary triple vortex, observed in a cylindrical plasma, is presented. The concentration of neutrals, which is rather high in the experiment, turns out to be of crucial importance due to a spatially dependent distribution. In the radial direction the neutral concentration is paraboliclike, yielding an effective radial force directed towards the axis of the system. This neutral force causes the rotation of the plasma in the direction which is opposite to theẼ E B B drift. The stationary triple vortex develops for a starting Gaussian-density distribution and a rigid-body rotation of the plasma column.
Simulation results of three-dimensional (3D) stationary magnetohydrodynamic (MHD) bow-shock flows... more Simulation results of three-dimensional (3D) stationary magnetohydrodynamic (MHD) bow-shock flows around perfectly conducting spheres are presented. For strong upstream magnetic field a new complex bow-shock flow topology arises consisting of two consecutive interacting shock fronts. It is shown that the leading shock front contains a segment of intermediate 1-3 shock type. This is the first confirmation in 3D that intermediate shocks, which were believed to be unphysical for a long time, can be formed and can persist for small-dissipation MHD in a realistic flow configuration.
The propagation of compressional MHD waves is studied for an externally driven system. It is assu... more The propagation of compressional MHD waves is studied for an externally driven system. It is assumed that the combined action of the external sources and sinks of the entropy results in the harmonic oscillation of the entropy (and temperature) in the system. It is found that with the appropriate resonant conditions fast and slow waves get amplified due to the phenomenon of parametric resonance. Besides, it is shown that the considered waves are mutually coupled as a consequence of the nonequilibrium state of the background medium. The coupling is strongest when the plasma β ≈ 1. The proposed formalism is sufficiently general and can be applied for many dynamical systems, both under terrestrial and astrophysical conditions.
A purely kinetic instability of the dust acoustic mode in inhomogeneous plasmas is discussed. In ... more A purely kinetic instability of the dust acoustic mode in inhomogeneous plasmas is discussed. In the presence of a magnetic field, electrons and ions may be magnetized while at the same time dust grains may remain unmagnetized. Although the dynamics of the light species is strongly affected by the magnetic field, the dust acoustic mode may still propagate in practically any direction. The inhomogeneity implies a source of free energy for an instability that develops through the diamagnetic drift effects of the magnetized species. It is shown that this may be a powerful mechanism for the excitation of dust acoustic waves. The analysis presented in the work is also directly applicable to plasmas containing both positive and negative ions and electrons, provided that at least one of the two ion species is unmagnetized.
It is shown that nonlinear three-wave interaction, described by vector-product type nonlinearitie... more It is shown that nonlinear three-wave interaction, described by vector-product type nonlinearities, in pair plasmas implies much more restrictive conditions for a double energy transfer, as compared to electron-ion plasmas. PACS numbers: 52.35.Mw, 52.30.Ex, 52.27.Ep a) [email protected] b) [email protected]
An analysis of the temperature-gradient-driven ͑ i ͒ instability of drift waves in dusty plasma i... more An analysis of the temperature-gradient-driven ͑ i ͒ instability of drift waves in dusty plasma is presented. Various limits that allow for the coupling of the drift wave with the dynamics of dust grains are discussed. In particular, the cases of tiny (magnetized) and relatively heavy (unmagnetized) grains are studied. It is shown that in both limits the behavior of the i mode is considerably affected by the dust dynamics. The growth rate turns out to be higher in the presence of dust, and the instability threshold is lower, resulting in a more unstable plasma.
Response of nonuniform magnetized plasma to strongly nonlinear electromagnetic perturbations driv... more Response of nonuniform magnetized plasma to strongly nonlinear electromagnetic perturbations driven by nonuniform £ows is studied.Various types of coherent structures with spatial scales of the order of the electron skin depth are found carried by the £ow or propagating through the plasma, with spatial scales measured in tens of kilometers for the magnetotail region.
Monthly Notices of the Royal Astronomical Society, 2009
The heating of the plasma in the solar atmosphere is discussed within both frameworks of fluid an... more The heating of the plasma in the solar atmosphere is discussed within both frameworks of fluid and kinetic drift wave theory. We show that the basic ingredient necessary for the heating is the presence of density gradients in the direction perpendicular to the magnetic field vector. Such density gradients are a source of free energy for the excitation of drift waves. We use only well established basic theory, verified experimentally in laboratory plasmas. Two mechanisms of the energy exchange and heating are shown to take place simultaneously: one due to the Landau effect in the direction parallel to the magnetic field, and another one, stochastic heating, in the perpendicular direction. The stochastic heating i) is due to the electrostatic nature of the waves, ii) is more effective on ions than on electrons, iii) acts predominantly in the perpendicular direction, iv) heats heavy ions more efficiently than lighter ions, and v) may easily provide a drift wave heating rate that is orders of magnitude above the value that is presently believed to be sufficient for the coronal heating, i.e., ≃ 6 · 10 −5 J/(m 3 s) for active regions and ≃ 8 · 10 −6 J/(m 3 s) for coronal holes. This heating acts naturally through well known effects that are, however, beyond the current standard models and theories.
Monthly Notices of the Royal Astronomical Society, 2014
We investigate electrostatic plasma instabilities of Farley-Buneman (FB) type driven by quasistat... more We investigate electrostatic plasma instabilities of Farley-Buneman (FB) type driven by quasistationary neutral gas flows in the solar chromosphere. The role of these instabilities in the chromosphere is clarified. We find that the destabilizing ion thermal effect is highly reduced by the Coulomb collisions and can be ignored for the chromospheric FB-type instabilities. In contrast, the destabilizing electron thermal effect is important and causes a significant reduction of the neutral drag velocity triggering the instability. The resulting threshold velocity is found as function of chromospheric height. Our results indicate that the FB-type instabilities are still less efficient in the global chromospheric heating than the Joule dissipation of the currents driving these instabilities. This conclusion does not exclude the possibility that the FB-type instabilities develop in the places where the cross-field currents overcome the threshold value and contribute to the heating locally. Typical length-scales of plasma density fluctuations produced by these instabilities are determined by the wavelengths of unstable modes, which are in the range 10-10 2 cm in the lower chromosphere and 10 2 -10 3 cm in the upper chromosphere. These results suggest that the decimetric radio waves undergoing scattering (scintillations) by these plasma irregularities can serve as a tool for remote probing of the solar chromosphere at different heights.
Monthly Notices of the Royal Astronomical Society, 2010
The efficiency of nonmodal self-heating by acoustic wave perturbations is examined. Considering d... more The efficiency of nonmodal self-heating by acoustic wave perturbations is examined. Considering different kinds of kinematically complex velocity patterns we show that nonmodal instabilities arising in these inhomogeneous flows may lead to significant amplification of acoustic waves. Subsequently, the presence of viscous dissipation damps these amplified waves and causes the energy transfer back to the background flow in the form of heat; viz. closes the "self-heating" cycle and contributes to the net heating of the flow patterns and the chromospheric network as a whole. The acoustic selfheating depends only on the presence of kinematically complex flows and dissipation. It is argued that together with other mechanisms of nonlinear nature the self-heating may be a probable additinal mechanism of nonmagnetic chromospheric heating in the Sun and other solar-type stars with slow rotation and extended convective regions.
Monthly Notices of the Royal Astronomical Society, 2010
Non-thermal particle distributions of kappa type are frequently encountered in collisionless plas... more Non-thermal particle distributions of kappa type are frequently encountered in collisionless plasmas from space. The electromagnetic emissions coming from space are believed to originate in the counterstreaming structures of plasmas, which are ubiquitous in many astrophysical systems. Here, we investigate the dispersion properties and the stability of a counterstreaming plasma system with temperature anisotropies modelled by a bi-kappa distribution function. The numerical evaluation of parallel modes shows growth rates lower than those obtained for Maxwellian plasmas, with a strong dependence on the spectral index of the particle distribution function. If all other parameters are known, measuring the instability growth time can provide a possible tool for the determination of the spectral index κ.
Monthly Notices of the Royal Astronomical Society, 2000
The electrostatic instabilities driven by the gradients of the density, temperature and magnetic ... more The electrostatic instabilities driven by the gradients of the density, temperature and magnetic field, are discussed in their application to solar magnetic structures. Strongly growing modes are found for some typical plasma parameters. These instabilities i) imply the presence of electric fields that can accelerate the plasma particles in both perpendicular and parallel directions with respect to the magnetic field vector, and ii) can stochastically heat ions. The perpendicular acceleration is to the leading order determined by the E × B-drift acting equally on both ions and electrons, while the parallel acceleration is most effective on electrons. The experimentally confirmed stochastic heating is shown to act mainly in the direction perpendicular to the magnetic field vector and acts stronger on heavier ions. The energy release rate and heating may exceed for several orders of magnitude the value accepted as necessary for a selfsustained heating in the solar corona. The energy source for both the acceleration and the heating is stored in the mentioned background gradients.
Monthly Notices of the Royal Astronomical Society, 2010
In the solar corona, several mechanisms of the drift wave instability can make the mode growing u... more In the solar corona, several mechanisms of the drift wave instability can make the mode growing up to amplitudes at which particle acceleration and stochastic heating by the drift wave take place. The stochastic heating, well known from laboratory plasma physics where it has been confirmed in numerous experiments, has been completely ignored in past studies of coronal heating. However, in the present study and in our very recent works it has been shown that the inhomogeneous coronal plasma is, in fact, a perfect environment for fast growing drift waves. As a matter of fact, the large growth rates are typically of the same order as the wave frequency. The consequent heating rates may exceed the required values for a sustained coronal heating by several orders of magnitude. Some aspects of these phenomena are investigated here. In particular the analysis of the particle dynamics within the growing wave is compared with the corresponding fluid analysis. While both of them predict the stochastic heating, the threshold for the heating obtained from the single particle analysis is higher. The explanation for this effect is given.
Monthly Notices of the Royal Astronomical Society, 2014
The electron cyclotron emissions represent a useful tool in the diagnostics of fusion plasmas and... more The electron cyclotron emissions represent a useful tool in the diagnostics of fusion plasmas and space plasma fluctuations. The instability which enhances the whistler-cyclotron modes is driven in the presence of an ambient regular magnetic field by an excess of transverse kinetic energy of plasma particles. Previous studies have modelled the anisotropic particles with a bi-Maxwellian or a bi-Kappa distribution function and found a suppression of this instability in the presence of suprathermal tails. Here, the anisotropic plasma is modelled with a product-bi-Kappa distribution, with the advantage that this distribution function enables the use of two different spectral indices in the main directions, κ = κ ⊥ , and permits further characterization of kappa populations and their excitations. The exact numerical values of the growth rates and the instability threshold are derived and contrasted with those for a simple bi-Kappa and a bi-Maxwellian, using plasma parameters and magnetic fields relevant for the solar and terrestrial environments.
In this study, we test the flux rope paradigm by performing a "blind" reconstruction of the magne... more In this study, we test the flux rope paradigm by performing a "blind" reconstruction of the magnetic field structure of a simulated interplanetary coronal mass ejection (ICME). The ICME is the result of a magneto-hydrodynamic (MHD) numerical simulation and does not exhibit much magnetic twist, but appears to have some characteristics of a magnetic cloud, due to a writhe in the magnetic field lines. We use the Grad-Shafranov technique with simulated spacecraft measurements at two different distances and compare the reconstructed magnetic field with that of the ICME in the simulation. While the reconstructed magnetic field is similar to the simulated one as seen in two dimensions, it yields a helically twisted magnetic field in three dimensions. To further verify the results, we perform the reconstruction at three different position angles at every distance point, and all results come into agreement. This work demonstrates that the current paradigm of associating magnetic clouds with flux ropes may have to be revised.
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Papers by Stefaan Poedts