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I Rogachevskii - One of the best experts on this subject based on the ideXlab platform.
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active region formation through the negative effective Magnetic Pressure instability
Solar Physics, 2013Co-Authors: Axel Brandenburg, N Kleeorin, I Rogachevskii, Koen Kemel, Dhrubaditya MitraAbstract:The negative effective Magnetic-Pressure instability operates on scales encompassing many turbulent eddies, which correspond to convection cells in the Sun. This instability is discussed here in connection with the formation of active regions near the surface layers of the Sun. This instability is related to the negative contribution of turbulence to the mean Magnetic Pressure that causes the formation of large-scale Magnetic structures. For an isothermal layer, direct numerical simulations and mean-field simulations of this phenomenon are shown to agree in many details, for example the onset of the instability occurs at the same depth. This depth increases with increasing field strength, such that the growth rate of this instability is independent of the field strength, provided the Magnetic structures are fully contained within the domain. A linear stability analysis is shown to support this finding. The instability also leads to a redistribution of turbulent intensity and gas Pressure that could provide direct observational signatures.
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negative effective Magnetic Pressure in turbulent convection
Monthly Notices of the Royal Astronomical Society, 2012Co-Authors: Petri J Kapyla, Axel Brandenburg, N Kleeorin, M J Mantere, I RogachevskiiAbstract:We investigate the effects of weakly and strongly stratified turbulent convection on the mean effective Lorentz force, and especially on the mean effective Magnetic Pressure. Earlier studies with isotropically forced non-stratified and stratified turbulence have shown that the contribution of the turbulence to the mean Magnetic Pressure is negative for mean horizontal Magnetic fields that are smaller than the equipartition strength, so that the effective mean Magnetic Pressure that takes into account the turbulence effects can be negative. Compared with earlier cases of forced turbulence with an isothermal equation of state, we find that the turbulence effect is similar to or even stronger in the present case of turbulent convection. This is argued to be due to the anisotropy of turbulence in the vertical direction. Another important difference compared with earlier studies is the presence of an evolution equation for the specific entropy. Mean-field modelling with entropy evolution indicates that the negative effective Magnetic Pressure can still lead to a large-scale instability which forms local flux concentrations, even though the specific entropy evolution tends to have a stabilizing effect when applied to a stably stratified (e.g. isothermal) layer. It is argued that this large-scale instability could be important for the formation of solar large-scale Magnetic structures such as active regions.
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the negative effective Magnetic Pressure in stratified forced turbulence
The Astrophysical Journal, 2012Co-Authors: Axel Brandenburg, N Kleeorin, Koen Kemel, I RogachevskiiAbstract:To understand the basic mechanism of the formation of Magnetic flux concentrations, we determine by direct numerical simulations the turbulence contributions to the mean Magnetic Pressure in a strongly stratified isothermal layer with large plasma beta, where a weak uniform horizontal mean Magnetic field is applied. The negative contribution of turbulence to the effective mean Magnetic Pressure is determined for strongly stratified forced turbulence over a range of values of Magnetic Reynolds and Prandtl numbers. Small-scale dynamo action is shown to reduce the negative effect of turbulence on the effective mean Magnetic Pressure. However, the turbulence coefficients describing the negative effective Magnetic Pressure phenomenon are found to converge for Magnetic Reynolds numbers between 60 and 600, which is the largest value considered here. In all these models, the turbulent intensity is arranged to be nearly independent of height, so the kinetic energy density decreases with height due to the decrease in density. In a second series of numerical experiments, the turbulent intensity increases with height such that the turbulent kinetic energy density is nearly independent of height. Turbulent Magnetic diffusivity and turbulent pumping velocity are determined with the test-field method for both cases. The vertical profile of the turbulent Magnetic diffusivity is found to agree with what is expected based on simple mixing length expressions. Turbulent pumping is shown to be down the gradient of turbulent Magnetic diffusivity, but it is twice as large as expected. Corresponding numerical mean-field models are used to show that a large-scale instability can occur in both cases, provided the degree of scale separation is large enough and hence the turbulent Magnetic diffusivity small enough.
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active region formation through the negative effective Magnetic Pressure instability
arXiv: Solar and Stellar Astrophysics, 2012Co-Authors: Koen Kemel, Axel Brandenburg, N Kleeorin, Dhrubaditya Mitra, I RogachevskiiAbstract:The negative effective Magnetic Pressure instability operates on scales encompassing many turbulent eddies and is here discussed in connection with the formation of active regions near the surface layers of the Sun. This instability is related to the negative contribution of turbulence to the mean Magnetic Pressure that causes the formation of large-scale Magnetic structures. For an isothermal layer, direct numerical simulations and mean-field simulations of this phenomenon are shown to agree in many details in that their onset occurs at the same depth. This depth increases with increasing field strength, such that the maximum growth rate of this instability is independent of the field strength, provided the Magnetic structures are fully contained within the domain. A linear stability analysis is shown to support this finding. The instability also leads to a redistribution of turbulent intensity and gas Pressure that could provide direct observational signatures.
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properties of the negative effective Magnetic Pressure instability
Astronomische Nachrichten, 2012Co-Authors: Koen Kemel, Axel Brandenburg, N Kleeorin, I RogachevskiiAbstract:As was demonstrated in earlier studies, turbulence can result in a negative contribution to the effective mean Magnetic Pressure, which, in turn, can cause a large-scale instability. In this study, ...
Axel Brandenburg - One of the best experts on this subject based on the ideXlab platform.
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active region formation through the negative effective Magnetic Pressure instability
Solar Physics, 2013Co-Authors: Axel Brandenburg, N Kleeorin, I Rogachevskii, Koen Kemel, Dhrubaditya MitraAbstract:The negative effective Magnetic-Pressure instability operates on scales encompassing many turbulent eddies, which correspond to convection cells in the Sun. This instability is discussed here in connection with the formation of active regions near the surface layers of the Sun. This instability is related to the negative contribution of turbulence to the mean Magnetic Pressure that causes the formation of large-scale Magnetic structures. For an isothermal layer, direct numerical simulations and mean-field simulations of this phenomenon are shown to agree in many details, for example the onset of the instability occurs at the same depth. This depth increases with increasing field strength, such that the growth rate of this instability is independent of the field strength, provided the Magnetic structures are fully contained within the domain. A linear stability analysis is shown to support this finding. The instability also leads to a redistribution of turbulent intensity and gas Pressure that could provide direct observational signatures.
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negative effective Magnetic Pressure in turbulent convection
Monthly Notices of the Royal Astronomical Society, 2012Co-Authors: Petri J Kapyla, Axel Brandenburg, N Kleeorin, M J Mantere, I RogachevskiiAbstract:We investigate the effects of weakly and strongly stratified turbulent convection on the mean effective Lorentz force, and especially on the mean effective Magnetic Pressure. Earlier studies with isotropically forced non-stratified and stratified turbulence have shown that the contribution of the turbulence to the mean Magnetic Pressure is negative for mean horizontal Magnetic fields that are smaller than the equipartition strength, so that the effective mean Magnetic Pressure that takes into account the turbulence effects can be negative. Compared with earlier cases of forced turbulence with an isothermal equation of state, we find that the turbulence effect is similar to or even stronger in the present case of turbulent convection. This is argued to be due to the anisotropy of turbulence in the vertical direction. Another important difference compared with earlier studies is the presence of an evolution equation for the specific entropy. Mean-field modelling with entropy evolution indicates that the negative effective Magnetic Pressure can still lead to a large-scale instability which forms local flux concentrations, even though the specific entropy evolution tends to have a stabilizing effect when applied to a stably stratified (e.g. isothermal) layer. It is argued that this large-scale instability could be important for the formation of solar large-scale Magnetic structures such as active regions.
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the negative effective Magnetic Pressure in stratified forced turbulence
The Astrophysical Journal, 2012Co-Authors: Axel Brandenburg, N Kleeorin, Koen Kemel, I RogachevskiiAbstract:To understand the basic mechanism of the formation of Magnetic flux concentrations, we determine by direct numerical simulations the turbulence contributions to the mean Magnetic Pressure in a strongly stratified isothermal layer with large plasma beta, where a weak uniform horizontal mean Magnetic field is applied. The negative contribution of turbulence to the effective mean Magnetic Pressure is determined for strongly stratified forced turbulence over a range of values of Magnetic Reynolds and Prandtl numbers. Small-scale dynamo action is shown to reduce the negative effect of turbulence on the effective mean Magnetic Pressure. However, the turbulence coefficients describing the negative effective Magnetic Pressure phenomenon are found to converge for Magnetic Reynolds numbers between 60 and 600, which is the largest value considered here. In all these models, the turbulent intensity is arranged to be nearly independent of height, so the kinetic energy density decreases with height due to the decrease in density. In a second series of numerical experiments, the turbulent intensity increases with height such that the turbulent kinetic energy density is nearly independent of height. Turbulent Magnetic diffusivity and turbulent pumping velocity are determined with the test-field method for both cases. The vertical profile of the turbulent Magnetic diffusivity is found to agree with what is expected based on simple mixing length expressions. Turbulent pumping is shown to be down the gradient of turbulent Magnetic diffusivity, but it is twice as large as expected. Corresponding numerical mean-field models are used to show that a large-scale instability can occur in both cases, provided the degree of scale separation is large enough and hence the turbulent Magnetic diffusivity small enough.
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active region formation through the negative effective Magnetic Pressure instability
arXiv: Solar and Stellar Astrophysics, 2012Co-Authors: Koen Kemel, Axel Brandenburg, N Kleeorin, Dhrubaditya Mitra, I RogachevskiiAbstract:The negative effective Magnetic Pressure instability operates on scales encompassing many turbulent eddies and is here discussed in connection with the formation of active regions near the surface layers of the Sun. This instability is related to the negative contribution of turbulence to the mean Magnetic Pressure that causes the formation of large-scale Magnetic structures. For an isothermal layer, direct numerical simulations and mean-field simulations of this phenomenon are shown to agree in many details in that their onset occurs at the same depth. This depth increases with increasing field strength, such that the maximum growth rate of this instability is independent of the field strength, provided the Magnetic structures are fully contained within the domain. A linear stability analysis is shown to support this finding. The instability also leads to a redistribution of turbulent intensity and gas Pressure that could provide direct observational signatures.
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properties of the negative effective Magnetic Pressure instability
Astronomische Nachrichten, 2012Co-Authors: Koen Kemel, Axel Brandenburg, N Kleeorin, I RogachevskiiAbstract:As was demonstrated in earlier studies, turbulence can result in a negative contribution to the effective mean Magnetic Pressure, which, in turn, can cause a large-scale instability. In this study, ...
Koen Kemel - One of the best experts on this subject based on the ideXlab platform.
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active region formation through the negative effective Magnetic Pressure instability
Solar Physics, 2013Co-Authors: Axel Brandenburg, N Kleeorin, I Rogachevskii, Koen Kemel, Dhrubaditya MitraAbstract:The negative effective Magnetic-Pressure instability operates on scales encompassing many turbulent eddies, which correspond to convection cells in the Sun. This instability is discussed here in connection with the formation of active regions near the surface layers of the Sun. This instability is related to the negative contribution of turbulence to the mean Magnetic Pressure that causes the formation of large-scale Magnetic structures. For an isothermal layer, direct numerical simulations and mean-field simulations of this phenomenon are shown to agree in many details, for example the onset of the instability occurs at the same depth. This depth increases with increasing field strength, such that the growth rate of this instability is independent of the field strength, provided the Magnetic structures are fully contained within the domain. A linear stability analysis is shown to support this finding. The instability also leads to a redistribution of turbulent intensity and gas Pressure that could provide direct observational signatures.
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the negative effective Magnetic Pressure in stratified forced turbulence
The Astrophysical Journal, 2012Co-Authors: Axel Brandenburg, N Kleeorin, Koen Kemel, I RogachevskiiAbstract:To understand the basic mechanism of the formation of Magnetic flux concentrations, we determine by direct numerical simulations the turbulence contributions to the mean Magnetic Pressure in a strongly stratified isothermal layer with large plasma beta, where a weak uniform horizontal mean Magnetic field is applied. The negative contribution of turbulence to the effective mean Magnetic Pressure is determined for strongly stratified forced turbulence over a range of values of Magnetic Reynolds and Prandtl numbers. Small-scale dynamo action is shown to reduce the negative effect of turbulence on the effective mean Magnetic Pressure. However, the turbulence coefficients describing the negative effective Magnetic Pressure phenomenon are found to converge for Magnetic Reynolds numbers between 60 and 600, which is the largest value considered here. In all these models, the turbulent intensity is arranged to be nearly independent of height, so the kinetic energy density decreases with height due to the decrease in density. In a second series of numerical experiments, the turbulent intensity increases with height such that the turbulent kinetic energy density is nearly independent of height. Turbulent Magnetic diffusivity and turbulent pumping velocity are determined with the test-field method for both cases. The vertical profile of the turbulent Magnetic diffusivity is found to agree with what is expected based on simple mixing length expressions. Turbulent pumping is shown to be down the gradient of turbulent Magnetic diffusivity, but it is twice as large as expected. Corresponding numerical mean-field models are used to show that a large-scale instability can occur in both cases, provided the degree of scale separation is large enough and hence the turbulent Magnetic diffusivity small enough.
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active region formation through the negative effective Magnetic Pressure instability
arXiv: Solar and Stellar Astrophysics, 2012Co-Authors: Koen Kemel, Axel Brandenburg, N Kleeorin, Dhrubaditya Mitra, I RogachevskiiAbstract:The negative effective Magnetic Pressure instability operates on scales encompassing many turbulent eddies and is here discussed in connection with the formation of active regions near the surface layers of the Sun. This instability is related to the negative contribution of turbulence to the mean Magnetic Pressure that causes the formation of large-scale Magnetic structures. For an isothermal layer, direct numerical simulations and mean-field simulations of this phenomenon are shown to agree in many details in that their onset occurs at the same depth. This depth increases with increasing field strength, such that the maximum growth rate of this instability is independent of the field strength, provided the Magnetic structures are fully contained within the domain. A linear stability analysis is shown to support this finding. The instability also leads to a redistribution of turbulent intensity and gas Pressure that could provide direct observational signatures.
-
properties of the negative effective Magnetic Pressure instability
Astronomische Nachrichten, 2012Co-Authors: Koen Kemel, Axel Brandenburg, N Kleeorin, I RogachevskiiAbstract:As was demonstrated in earlier studies, turbulence can result in a negative contribution to the effective mean Magnetic Pressure, which, in turn, can cause a large-scale instability. In this study, ...
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detection of negative effective Magnetic Pressure instability in turbulence simulations
The Astrophysical Journal, 2011Co-Authors: Axel Brandenburg, N Kleeorin, Koen Kemel, Dhrubaditya Mitra, I RogachevskiiAbstract:We present the first numerical demonstration of the negative effective Magnetic Pressure instability in direct numerical simulations of stably stratified, externally forced, isothermal hydroMagnetic turbulence in the regime of large plasma beta. By the action of this instability, initially uniform horizontal Magnetic field forms flux concentrations whose scale is large compared to the turbulent scale. We further show that the Magnetic energy of these large-scale structures is only weakly dependent on the Magnetic Reynolds number. Our results support earlier mean-field calculations and analytic work that identified this instability. Applications to the formation of active regions in the Sun are discussed.
N Kleeorin - One of the best experts on this subject based on the ideXlab platform.
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active region formation through the negative effective Magnetic Pressure instability
Solar Physics, 2013Co-Authors: Axel Brandenburg, N Kleeorin, I Rogachevskii, Koen Kemel, Dhrubaditya MitraAbstract:The negative effective Magnetic-Pressure instability operates on scales encompassing many turbulent eddies, which correspond to convection cells in the Sun. This instability is discussed here in connection with the formation of active regions near the surface layers of the Sun. This instability is related to the negative contribution of turbulence to the mean Magnetic Pressure that causes the formation of large-scale Magnetic structures. For an isothermal layer, direct numerical simulations and mean-field simulations of this phenomenon are shown to agree in many details, for example the onset of the instability occurs at the same depth. This depth increases with increasing field strength, such that the growth rate of this instability is independent of the field strength, provided the Magnetic structures are fully contained within the domain. A linear stability analysis is shown to support this finding. The instability also leads to a redistribution of turbulent intensity and gas Pressure that could provide direct observational signatures.
-
negative effective Magnetic Pressure in turbulent convection
Monthly Notices of the Royal Astronomical Society, 2012Co-Authors: Petri J Kapyla, Axel Brandenburg, N Kleeorin, M J Mantere, I RogachevskiiAbstract:We investigate the effects of weakly and strongly stratified turbulent convection on the mean effective Lorentz force, and especially on the mean effective Magnetic Pressure. Earlier studies with isotropically forced non-stratified and stratified turbulence have shown that the contribution of the turbulence to the mean Magnetic Pressure is negative for mean horizontal Magnetic fields that are smaller than the equipartition strength, so that the effective mean Magnetic Pressure that takes into account the turbulence effects can be negative. Compared with earlier cases of forced turbulence with an isothermal equation of state, we find that the turbulence effect is similar to or even stronger in the present case of turbulent convection. This is argued to be due to the anisotropy of turbulence in the vertical direction. Another important difference compared with earlier studies is the presence of an evolution equation for the specific entropy. Mean-field modelling with entropy evolution indicates that the negative effective Magnetic Pressure can still lead to a large-scale instability which forms local flux concentrations, even though the specific entropy evolution tends to have a stabilizing effect when applied to a stably stratified (e.g. isothermal) layer. It is argued that this large-scale instability could be important for the formation of solar large-scale Magnetic structures such as active regions.
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the negative effective Magnetic Pressure in stratified forced turbulence
The Astrophysical Journal, 2012Co-Authors: Axel Brandenburg, N Kleeorin, Koen Kemel, I RogachevskiiAbstract:To understand the basic mechanism of the formation of Magnetic flux concentrations, we determine by direct numerical simulations the turbulence contributions to the mean Magnetic Pressure in a strongly stratified isothermal layer with large plasma beta, where a weak uniform horizontal mean Magnetic field is applied. The negative contribution of turbulence to the effective mean Magnetic Pressure is determined for strongly stratified forced turbulence over a range of values of Magnetic Reynolds and Prandtl numbers. Small-scale dynamo action is shown to reduce the negative effect of turbulence on the effective mean Magnetic Pressure. However, the turbulence coefficients describing the negative effective Magnetic Pressure phenomenon are found to converge for Magnetic Reynolds numbers between 60 and 600, which is the largest value considered here. In all these models, the turbulent intensity is arranged to be nearly independent of height, so the kinetic energy density decreases with height due to the decrease in density. In a second series of numerical experiments, the turbulent intensity increases with height such that the turbulent kinetic energy density is nearly independent of height. Turbulent Magnetic diffusivity and turbulent pumping velocity are determined with the test-field method for both cases. The vertical profile of the turbulent Magnetic diffusivity is found to agree with what is expected based on simple mixing length expressions. Turbulent pumping is shown to be down the gradient of turbulent Magnetic diffusivity, but it is twice as large as expected. Corresponding numerical mean-field models are used to show that a large-scale instability can occur in both cases, provided the degree of scale separation is large enough and hence the turbulent Magnetic diffusivity small enough.
-
active region formation through the negative effective Magnetic Pressure instability
arXiv: Solar and Stellar Astrophysics, 2012Co-Authors: Koen Kemel, Axel Brandenburg, N Kleeorin, Dhrubaditya Mitra, I RogachevskiiAbstract:The negative effective Magnetic Pressure instability operates on scales encompassing many turbulent eddies and is here discussed in connection with the formation of active regions near the surface layers of the Sun. This instability is related to the negative contribution of turbulence to the mean Magnetic Pressure that causes the formation of large-scale Magnetic structures. For an isothermal layer, direct numerical simulations and mean-field simulations of this phenomenon are shown to agree in many details in that their onset occurs at the same depth. This depth increases with increasing field strength, such that the maximum growth rate of this instability is independent of the field strength, provided the Magnetic structures are fully contained within the domain. A linear stability analysis is shown to support this finding. The instability also leads to a redistribution of turbulent intensity and gas Pressure that could provide direct observational signatures.
-
properties of the negative effective Magnetic Pressure instability
Astronomische Nachrichten, 2012Co-Authors: Koen Kemel, Axel Brandenburg, N Kleeorin, I RogachevskiiAbstract:As was demonstrated in earlier studies, turbulence can result in a negative contribution to the effective mean Magnetic Pressure, which, in turn, can cause a large-scale instability. In this study, ...
Ramesh Narayan - One of the best experts on this subject based on the ideXlab platform.
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electron heating by the ion cyclotron instability in collisionless accretion flows i compression driven instabilities and the electron heating mechanism
The Astrophysical Journal, 2015Co-Authors: Lorenzo Sironi, Ramesh NarayanAbstract:In systems accreting well below the Eddington rate, such as the central black hole in the Milky Way (Sgr A*), the plasma in the innermost regions of the disk is believed to be collisionless and have two temperatures, with the ions substantially hotter than the electrons. However, whether a collisionless faster-than-Coulomb energy transfer mechanism exists in two-temperature accretion flows is still an open question. We study the physics of electron heating during the growth of ion velocity-space instabilities by means of multidimensional, fully kinetic, particle-in-cell (PIC) simulations. A background large-scale compression—embedded in a novel form of the PIC equations—continuously amplifies the field. This constantly drives a Pressure anisotropy P ⊥ > P ∥ because of the adiabatic invariance of the particle Magnetic moments. We find that, for ion plasma beta values β0i ~ 5-30 appropriate for the midplane of low-luminosity accretion flows (here, β0i is the ratio of ion thermal Pressure to Magnetic Pressure), mirror modes dominate if the electron-to-proton temperature ratio is T 0e /T 0i 0.2, whereas for T 0e /T 0i 0.2 the ion cyclotron instability triggers the growth of strong Alfven-like waves, which pitch-angle scatter the ions to maintain marginal stability. We develop an analytical model of electron heating during the growth of the ion cyclotron instability, which we validate with PIC simulations. We find that for cold electrons (β0e 2 me /mi , where β0e is the ratio of electron thermal Pressure to Magnetic Pressure), the electron energy gain is controlled by the magnitude of the E-cross-B velocity induced by the ion cyclotron waves. This term is independent of the initial electron temperature, so it provides a solid energy floor even for electrons starting with extremely low temperatures. On the other hand, the electron energy gain for β0e 2 me /mi —governed by the conservation of the particle Magnetic moment in the growing fields of the instability—is proportional to the initial electron temperature, and it scales with the Magnetic energy of ion cyclotron waves. Our results have implications for two-temperature accretion flows as well as for solar wind and intracluster plasmas.
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electron heating by the ion cyclotron instability in collisionless accretion flows i compression driven instabilities and the electron heating mechanism
The Astrophysical Journal, 2015Co-Authors: Lorenzo Sironi, Ramesh NarayanAbstract:In systems accreting well below the Eddington rate, such as the central black hole in the Milky Way (Sgr A*), the plasma in the innermost regions of the disk is believed to be collisionless and have two temperatures, with the ions substantially hotter than the electrons. However, whether a collisionless faster-than-Coulomb energy transfer mechanism exists in two-temperature accretion flows is still an open question. We study the physics of electron heating during the growth of ion velocity-space instabilities by means of multidimensional, fully kinetic, particle-in-cell (PIC) simulations. A background large-scale compression—embedded in a novel form of the PIC equations—continuously amplifies the field. This constantly drives a Pressure anisotropy P ⊥ > P ∥ because of the adiabatic invariance of the particle Magnetic moments. We find that, for ion plasma beta values β0i ~ 5-30 appropriate for the midplane of low-luminosity accretion flows (here, β0i is the ratio of ion thermal Pressure to Magnetic Pressure), mirror modes dominate if the electron-to-proton temperature ratio is T 0e /T 0i 0.2, whereas for T 0e /T 0i 0.2 the ion cyclotron instability triggers the growth of strong Alfven-like waves, which pitch-angle scatter the ions to maintain marginal stability. We develop an analytical model of electron heating during the growth of the ion cyclotron instability, which we validate with PIC simulations. We find that for cold electrons (β0e 2 me /mi , where β0e is the ratio of electron thermal Pressure to Magnetic Pressure), the electron energy gain is controlled by the magnitude of the E-cross-B velocity induced by the ion cyclotron waves. This term is independent of the initial electron temperature, so it provides a solid energy floor even for electrons starting with extremely low temperatures. On the other hand, the electron energy gain for β0e 2 me /mi —governed by the conservation of the particle Magnetic moment in the growing fields of the instability—is proportional to the initial electron temperature, and it scales with the Magnetic energy of ion cyclotron waves. Our results have implications for two-temperature accretion flows as well as for solar wind and intracluster plasmas.
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numerical simulation of hot accretion flows iii revisiting wind properties using trajectory approach
arXiv: High Energy Astrophysical Phenomena, 2015Co-Authors: Feng Yuan, Zhaoming Gan, Ramesh Narayan, Aleksander Sadowski, Xuening BaiAbstract:Previous MHD simulations have shown that wind must exist in black hole hot accretion flows. In this paper, we continue our study by investigating the detailed properties of wind, such as mass flux and poloidal speed, and the mechanism of wind production. For this aim, we make use of a three dimensional GRMHD simulation of hot accretion flows around a Schwarzschild black hole. The simulation is designed so that the Magnetic flux is not accumulated significantly around the black hole. To distinguish real wind from turbulent outflows, we track the trajectories of the virtual Largrangian particles from simulation data. We find two types of real outflows, i.e., a quasi-relativistic jet close to the axis and a sub-relativistic wind subtending a much larger solid angle. Most of the wind originates from the surface layer of the accretion flow. The poloidal wind speed almost remains constant once they are produced, but the flux-weighted wind speed roughly follows $v_{\rm p, wind}(r)\approx 0.25 v_k(r)$. The mass flux of jet is much lower but the speed is much higher, $v_{\rm p,jet}\sim (0.3-0.4) c$. Consequently, both the energy and momentum fluxes of the wind are much larger than those of the jet. We find that the wind is produced and accelerated primarily by the combination of centrifugal force and Magnetic Pressure gradient, while the jet is mainly accelerated by Magnetic Pressure gradient. Finally, we find that the wind production efficiency $\epsilon_{\rm wind}\equiv\dot{E}_{\rm wind}/\dot{M}_{\rm BH}c^2\sim 1/1000$, in good agreement with the value required from large-scale galaxy simulations with AGN feedback.