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Eliot Quataert - One of the best experts on this subject based on the ideXlab platform.
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pic simulations of velocity space instabilities in a decreasing magnetic field viscosity and Thermal Conduction
The Astrophysical Journal, 2018Co-Authors: Mario A. Riquelme, Eliot Quataert, Daniel VerscharenAbstract:We use particle-in-cell (PIC) simulations of a collisionless, electron–ion plasma with a decreasing background magnetic field, B, to study the effect of velocity-space instabilities on the viscous heating and Thermal Conduction of the plasma. If |B| decreases, the adiabatic invariance of the magnetic moment gives rise to pressure anisotropies with p_{||,j} > p_{\perp,j} (p_{||,j} and p_{\perp,j} represent the pressure of species j (electron or ion) parallel and perpendicular to B). Linear theory indicates that, for sufficiently large anisotropies, different velocity-space instabilities can be triggered. These instabilities in principle have the ability to pitch-angle scatter the particles, limiting the growth of the anisotropies. Our simulations focus on the nonlinear, saturated regime of the instabilities. This is done through the permanent decrease of |B| by an imposed plasma shear. We show that, in the regime 2 \lesssim \beta_j \lesssim 20 (\beta_j \equiv 8\pi p_j/B^2), the saturated ion and electron pressure anisotropies are controlled by the combined effect of the oblique ion firehose and the fast magnetosonic/whistler instabilities. These instabilities grow preferentially on the scale of the ion Larmor radius, and make \Delta p_e/p_{||,e} \approx \Delta p_i/p_{||,i} (where \Delta p_j=p_{\perp,j} - p_{||,j}). We also quantify the Thermal Conduction of the plasma by directly calculating the mean free path of electrons, {\lambda }_{e}, along the mean magnetic field, finding that {\lambda }_{e} depends strongly on whether |B| decreases or increases. Our results can be applied in studies of low-collisionality plasmas such as the solar wind, the intracluster medium, and some accretion disks around black holes.
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pic simulations of velocity space instabilities in a decreasing magnetic field viscosity and Thermal Conduction
arXiv: High Energy Astrophysical Phenomena, 2017Co-Authors: Mario A. Riquelme, Eliot Quataert, Daniel VerscharenAbstract:We use particle-in-cell (PIC) simulations of a collisionless, electron-ion plasma with a decreasing background magnetic field, $B$, to study the effect of velocity-space instabilities on the viscous heating and Thermal Conduction of the plasma. If $B$ decreases, the adiabatic invariance of the magnetic moment gives rise to pressure anisotropies with $p_{||,j} > p_{\perp,j}$ ($p_{||,j}$ and $p_{\perp,j}$ represent the pressure of species $j$ ($=i$ or $e$) parallel and perpendicular to the magnetic field). Linear theory indicates that, for sufficiently large anisotropies, different velocity-space instabilities can be triggered. These instabilities, which grow on scales comparable to the electron and ion Larmor radii, in principle have the ability to pitch-angle scatter the particles, limiting the growth of the anisotropies. Our PIC simulations focus on the nonlinear, saturated regime of the instabilities. This is done through the permanent decrease of the magnetic field by an imposed shear in the plasma. Our results show that, in the regime $2 \lesssim \beta_j \lesssim 20$ ($\beta_j \equiv 8\pi p_j/B^2$), the saturated ion and electron pressure anisotropies are controlled by the combined effect of the oblique ion firehose (OIF) and the fast magnetosonic/whistler (FM/W) instabilities. These instabilities grow preferentially on the ion Larmor radius scale, and make the ion and electron pressure anisotropies nearly equal: $\Delta p_e/p_{||,e} \approx \Delta p_i/p_{||,i}$ (where $\Delta p_j=p_{\perp,j} - p_{||,j}$). We also quantify the Thermal Conduction of the plasma by directly calculating the mean free path of electrons along the mean magnetic field, which we find strongly depends on whether $B$ decreases or increases. Our results can be applied in studies of low collisionality plasmas such as the solar wind, the intracluster medium, and some accretion disks around black holes.
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PIC Simulations of the Effect of Velocity Space Instabilities on Electron Viscosity and Thermal Conduction
The Astrophysical Journal, 2016Co-Authors: Mario A. Riquelme, Eliot Quataert, Daniel VerscharenAbstract:In low-collisionality plasmas, velocity-space instabilities are a key mechanism providing an effective collisionality for the plasma. We use particle-in-cell (PIC) simulations to study the interplay between electron and ion-scale velocity-space instabilities and their effect on electron pressure anisotropy, viscous heating, and Thermal Conduction. The adiabatic invariance of the magnetic moment in low-collisionality plasmas leads to pressure anisotropy, $p_{\perp,j} > p_{||,j}$, if the magnetic field $\vec{B}$ is amplified ($p_{\perp,j}$ and $p_{||,j}$ denote the pressure of species $j$ [electron, ion] perpendicular and parallel to $\vec{B}$). If the resulting anisotropy is large enough, it can in turn trigger small-scale plasma instabilities. Our PIC simulations explore the nonlinear regime of the mirror, ion-cyclotron, and electron whistler instabilities, through continuous amplification of the magnetic field $|\vec{B}|$ by an imposed shear in the plasma. In the regime $1 \lesssim \beta_j \lesssim 20$ ($\beta_j \equiv 8\pi p_j/|\vec{B}|^2$), the saturated electron pressure anisotropy, $\Delta p_e/p_{||,e}$, is determined mainly by the (electron-lengthscale) whistler marginal stability condition, with a modest factor of $\sim 1.5-2$ decrease due to the trapping of electrons by the mirrors. We explicitly calculate the mean free path of the electrons and ions along the mean magnetic field and provide a simple physical prescription for the mean free path and Thermal conductivity in low-collisionality $\beta_j \gtrsim 1$ plasmas. Our results imply that velocity-space instabilities likely decrease the Thermal conductivity of plasma in the outer parts of massive, hot, galaxy clusters. We also discuss the implications of our results for electron heating and Thermal Conduction in low-collisionality accretion flows onto black holes, including Sgr A* in the Galactic Center.
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the dynamics of rayleigh taylor stable and unstable contact discontinuities with anisotropic Thermal Conduction
Bulletin of the American Physical Society, 2012Co-Authors: Daniel Lecoanet, Ian J Parrish, Eliot QuataertAbstract:We study the effects of anisotropic Thermal Conduction along magnetic field lines on an accelerated contact discontinuity in a weakly collisional plasma. We first perform a linear stability analysis similar to that used to derive the Rayleigh–Taylor instability (RTI) dispersion relation. We find that anisotropic Conduction is only important for compressible modes, as modes in the Boussinesq limit are isoThermal. Modes grow faster in the presence of anisotropic Conduction, but growth rates do not change by more than a factor of the order of unity. We next run fully non-linear numerical simulations of a contact discontinuity with anisotropic Conduction. The non-linear evolution can be thought of as a superposition of three physical effects: temperature diffusion due to vertical Conduction, the RTI and the heat flux driven buoyancy instability (HBI). We find that the presence of the magnetoThermal instability (MTI) does not significantly affect the dynamics. In simulations with RTI-stable contact discontinuities, the temperature discontinuity spreads due to vertical heat Conduction. This occurs even for initially horizontal magnetic fields due to the initial vertical velocity perturbation and numerical mixing across the interface. The HBI slows this temperature diffusion by reorienting initially vertical magnetic field lines to a more horizontal geometry. In simulations with RTI-unstable contact discontinuities, the dynamics are initially governed by temperature diffusion, but the RTI becomes increasingly important at late times. We discuss the possible application of these results to supernova remnants, solar prominences and cold fronts in galaxy clusters.
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the dynamics of rayleigh taylor stable and unstable contact discontinuities with anisotropic Thermal Conduction
arXiv: Solar and Stellar Astrophysics, 2012Co-Authors: Daniel Lecoanet, Ian J Parrish, Eliot QuataertAbstract:We study the effects of anisotropic Thermal Conduction along magnetic field lines on an accelerated contact discontinuity in a weakly collisional plasma. We first perform a linear stability analysis similar to that used to derive the Rayleigh-Taylor instability (RTI) dispersion relation. We find that anisotropic Conduction is only important for compressible modes, as incompressible modes are isoThermal. Modes grow faster in the presence of anisotropic Conduction, but growth rates do not change by more than a factor of order unity. We next run fully non-linear numerical simulations of a contact discontinuity with anisotropic Conduction. The non-linear evolution can be thought of as a superposition of three physical effects: temperature diffusion due to vertical Conduction, the RTI, and the heat flux driven buoyancy instability (HBI). In simulations with RTI-stable contact discontinuities, the temperature discontinuity spreads due to vertical heat Conduction. This occurs even for initially horizontal magnetic fields due to the initial vertical velocity perturbation and numerical mixing across the interface. The HBI slows this temperature diffusion by reorienting initially vertical magnetic field lines to a more horizontal geometry. In simulations with RTI-unstable contact discontinuities, the dynamics are initially governed by temperature diffusion, but the RTI becomes increasingly important at late times. We discuss the possible application of these results to supernova remnants, solar prominences, and cold fronts in galaxy clusters.
Ian J Parrish - One of the best experts on this subject based on the ideXlab platform.
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the dynamics of rayleigh taylor stable and unstable contact discontinuities with anisotropic Thermal Conduction
Bulletin of the American Physical Society, 2012Co-Authors: Daniel Lecoanet, Ian J Parrish, Eliot QuataertAbstract:We study the effects of anisotropic Thermal Conduction along magnetic field lines on an accelerated contact discontinuity in a weakly collisional plasma. We first perform a linear stability analysis similar to that used to derive the Rayleigh–Taylor instability (RTI) dispersion relation. We find that anisotropic Conduction is only important for compressible modes, as modes in the Boussinesq limit are isoThermal. Modes grow faster in the presence of anisotropic Conduction, but growth rates do not change by more than a factor of the order of unity. We next run fully non-linear numerical simulations of a contact discontinuity with anisotropic Conduction. The non-linear evolution can be thought of as a superposition of three physical effects: temperature diffusion due to vertical Conduction, the RTI and the heat flux driven buoyancy instability (HBI). We find that the presence of the magnetoThermal instability (MTI) does not significantly affect the dynamics. In simulations with RTI-stable contact discontinuities, the temperature discontinuity spreads due to vertical heat Conduction. This occurs even for initially horizontal magnetic fields due to the initial vertical velocity perturbation and numerical mixing across the interface. The HBI slows this temperature diffusion by reorienting initially vertical magnetic field lines to a more horizontal geometry. In simulations with RTI-unstable contact discontinuities, the dynamics are initially governed by temperature diffusion, but the RTI becomes increasingly important at late times. We discuss the possible application of these results to supernova remnants, solar prominences and cold fronts in galaxy clusters.
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the dynamics of rayleigh taylor stable and unstable contact discontinuities with anisotropic Thermal Conduction
arXiv: Solar and Stellar Astrophysics, 2012Co-Authors: Daniel Lecoanet, Ian J Parrish, Eliot QuataertAbstract:We study the effects of anisotropic Thermal Conduction along magnetic field lines on an accelerated contact discontinuity in a weakly collisional plasma. We first perform a linear stability analysis similar to that used to derive the Rayleigh-Taylor instability (RTI) dispersion relation. We find that anisotropic Conduction is only important for compressible modes, as incompressible modes are isoThermal. Modes grow faster in the presence of anisotropic Conduction, but growth rates do not change by more than a factor of order unity. We next run fully non-linear numerical simulations of a contact discontinuity with anisotropic Conduction. The non-linear evolution can be thought of as a superposition of three physical effects: temperature diffusion due to vertical Conduction, the RTI, and the heat flux driven buoyancy instability (HBI). In simulations with RTI-stable contact discontinuities, the temperature discontinuity spreads due to vertical heat Conduction. This occurs even for initially horizontal magnetic fields due to the initial vertical velocity perturbation and numerical mixing across the interface. The HBI slows this temperature diffusion by reorienting initially vertical magnetic field lines to a more horizontal geometry. In simulations with RTI-unstable contact discontinuities, the dynamics are initially governed by temperature diffusion, but the RTI becomes increasingly important at late times. We discuss the possible application of these results to supernova remnants, solar prominences, and cold fronts in galaxy clusters.
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Thermal instability with anisotropic Thermal Conduction and adiabatic cosmic rays implications for cold filaments in galaxy clusters
The Astrophysical Journal, 2010Co-Authors: Prateek Sharma, Ian J Parrish, Eliot QuataertAbstract:Observations of the cores of nearby galaxy clusters show H? and molecular emission-line filaments. We argue that these are the result of local Thermal instability in a globally stable galaxy cluster core. We present local, high-resolution, two-dimensional magnetohydrodynamic simulations of Thermal instability for conditions appropriate to the intracluster medium (ICM); the simulations include anisotropic Thermal Conduction along magnetic field lines and adiabatic cosmic rays. Thermal Conduction suppresses Thermal instability along magnetic field lines on scales smaller than the Field length (10?kpc for the hot, diffuse ICM). We show that the Field length in the cold medium must be resolved both along and perpendicular to the magnetic field in order to obtain numerically converged results. Because of negligible Conduction perpendicular to the magnetic field, Thermal instability leads to fine scale structure in the perpendicular direction. Filaments of cold gas along magnetic field lines are thus a natural consequence of Thermal instability with anisotropic Thermal Conduction. This is true even in the fully nonlinear regime and even for dynamically weak magnetic fields. The filamentary structure in the cold gas is also imprinted on the diffuse X-ray-emitting plasma in the neighboring hot ICM. Nonlinearly, filaments of cold (~104?K) gas should have lengths (along the magnetic field) comparable to the Field length in the cold medium ~10?4 pc! Observations show, however, that the atomic filaments in clusters are far more extended, ~10?kpc. Cosmic-ray pressure support (or a small-scale turbulent magnetic pressure) may resolve this discrepancy: even a small cosmic-ray pressure in the diffuse ICM, ~10?4 of the Thermal pressure, can be adiabatically compressed to provide significant pressure support in cold filaments. This is qualitatively consistent with the large population of cosmic rays invoked to explain the atomic and molecular line ratios observed in filaments.
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Thermal instability with anisotropic Thermal Conduction and adiabatic cosmic rays implications for cold filaments in galaxy clusters
arXiv: Astrophysics of Galaxies, 2010Co-Authors: Prateek Sharma, Ian J Parrish, Eliot QuataertAbstract:Observations of the cores of nearby galaxy clusters show H$\alpha$ and molecular emission line filaments. We argue that these are the result of {\em local} Thermal instability in a {\em globally} stable galaxy cluster core. We present local, high resolution, two-dimensional magnetohydrodynamic simulations of Thermal instability for conditions appropriate to the intracluster medium (ICM); the simulations include Thermal Conduction along magnetic field lines and adiabatic cosmic rays. Thermal Conduction suppresses Thermal instability along magnetic field lines on scales smaller than the Field length ($\gtrsim$10 kpc for the hot, diffuse ICM). We show that the Field length in the cold medium must be resolved both along and perpendicular to the magnetic field in order to obtain numerically converged results. Because of negligible Conduction perpendicular to the magnetic field, Thermal instability leads to fine scale structure in the perpendicular direction. Filaments of cold gas along magnetic field lines are thus a natural consequence of Thermal instability with anisotropic Thermal Conduction. Nonlinearly, filaments of cold ($\sim 10^4$ K) gas should have lengths (along the magnetic field) comparable to the Field length in the cold medium $\sim 10^{-4}$ pc! Observations show, however, that the atomic filaments in clusters are far more extended, $\sim 10$ kpc. Cosmic ray pressure support (or a small scale turbulent magnetic pressure) may resolve this discrepancy: even a small cosmic ray pressure in the diffuse ICM, $\sim 10^{-4}$ of the Thermal pressure, can be adiabatically compressed to provide significant pressure support in cold filaments. This is qualitatively consistent with the large population of cosmic rays invoked to explain the atomic and molecular line ratios observed in filaments.
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simulations of magnetohydrodynamics instabilities in intracluster medium including anisotropic Thermal Conduction
The Astrophysical Journal, 2009Co-Authors: Tamara Bogdanovic, Christopher S Reynolds, Steven A Balbus, Ian J ParrishAbstract:We perform a suite of simulations of cooling cores in clusters of galaxies in order to investigate the effect of the recently discovered heat flux buoyancy instability (HBI) on the evolution of cores. Our models follow the three-dimensional magnetohydrodynamics of cooling cluster cores and capture the effects of anisotropic heat Conduction along the lines of magnetic field, but do not account for the cosmological setting of clusters or the presence of active galactic nuclei (AGNs). Our model clusters can be divided into three groups according to their final thermodynamical state: catastrophically collapsing cores, isoThermal cores, and an intermediate group whose final state is determined by the initial configuration of magnetic field. Modeled cores that are reminiscent of real cluster cores show evolution toward Thermal collapse on a timescale which is prolonged by a factor of ∼2–10 compared with the zero-Conduction cases. The principal effect of the HBI is to re-orient field lines to be perpendicular to the temperature gradient. Once the field has been wrapped up onto spherical surfaces surrounding the core, the core is insulated from further conductive heating (with the effective Thermal Conduction suppressed to less than 10 −2 of the Spitzer value) and proceeds to collapse. We speculate that, in real clusters, the central AGN and possibly mergers play the role of “stirrers,” periodically disrupting the azimuthal field structure and allowing Thermal Conduction to sporadically heat the core.
Prateek Sharma - One of the best experts on this subject based on the ideXlab platform.
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Thermal instability with anisotropic Thermal Conduction and adiabatic cosmic rays implications for cold filaments in galaxy clusters
The Astrophysical Journal, 2010Co-Authors: Prateek Sharma, Ian J Parrish, Eliot QuataertAbstract:Observations of the cores of nearby galaxy clusters show H? and molecular emission-line filaments. We argue that these are the result of local Thermal instability in a globally stable galaxy cluster core. We present local, high-resolution, two-dimensional magnetohydrodynamic simulations of Thermal instability for conditions appropriate to the intracluster medium (ICM); the simulations include anisotropic Thermal Conduction along magnetic field lines and adiabatic cosmic rays. Thermal Conduction suppresses Thermal instability along magnetic field lines on scales smaller than the Field length (10?kpc for the hot, diffuse ICM). We show that the Field length in the cold medium must be resolved both along and perpendicular to the magnetic field in order to obtain numerically converged results. Because of negligible Conduction perpendicular to the magnetic field, Thermal instability leads to fine scale structure in the perpendicular direction. Filaments of cold gas along magnetic field lines are thus a natural consequence of Thermal instability with anisotropic Thermal Conduction. This is true even in the fully nonlinear regime and even for dynamically weak magnetic fields. The filamentary structure in the cold gas is also imprinted on the diffuse X-ray-emitting plasma in the neighboring hot ICM. Nonlinearly, filaments of cold (~104?K) gas should have lengths (along the magnetic field) comparable to the Field length in the cold medium ~10?4 pc! Observations show, however, that the atomic filaments in clusters are far more extended, ~10?kpc. Cosmic-ray pressure support (or a small-scale turbulent magnetic pressure) may resolve this discrepancy: even a small cosmic-ray pressure in the diffuse ICM, ~10?4 of the Thermal pressure, can be adiabatically compressed to provide significant pressure support in cold filaments. This is qualitatively consistent with the large population of cosmic rays invoked to explain the atomic and molecular line ratios observed in filaments.
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Thermal instability with anisotropic Thermal Conduction and adiabatic cosmic rays implications for cold filaments in galaxy clusters
arXiv: Astrophysics of Galaxies, 2010Co-Authors: Prateek Sharma, Ian J Parrish, Eliot QuataertAbstract:Observations of the cores of nearby galaxy clusters show H$\alpha$ and molecular emission line filaments. We argue that these are the result of {\em local} Thermal instability in a {\em globally} stable galaxy cluster core. We present local, high resolution, two-dimensional magnetohydrodynamic simulations of Thermal instability for conditions appropriate to the intracluster medium (ICM); the simulations include Thermal Conduction along magnetic field lines and adiabatic cosmic rays. Thermal Conduction suppresses Thermal instability along magnetic field lines on scales smaller than the Field length ($\gtrsim$10 kpc for the hot, diffuse ICM). We show that the Field length in the cold medium must be resolved both along and perpendicular to the magnetic field in order to obtain numerically converged results. Because of negligible Conduction perpendicular to the magnetic field, Thermal instability leads to fine scale structure in the perpendicular direction. Filaments of cold gas along magnetic field lines are thus a natural consequence of Thermal instability with anisotropic Thermal Conduction. Nonlinearly, filaments of cold ($\sim 10^4$ K) gas should have lengths (along the magnetic field) comparable to the Field length in the cold medium $\sim 10^{-4}$ pc! Observations show, however, that the atomic filaments in clusters are far more extended, $\sim 10$ kpc. Cosmic ray pressure support (or a small scale turbulent magnetic pressure) may resolve this discrepancy: even a small cosmic ray pressure in the diffuse ICM, $\sim 10^{-4}$ of the Thermal pressure, can be adiabatically compressed to provide significant pressure support in cold filaments. This is qualitatively consistent with the large population of cosmic rays invoked to explain the atomic and molecular line ratios observed in filaments.
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anisotropic Thermal Conduction and the cooling flow problem in galaxy clusters
The Astrophysical Journal, 2009Co-Authors: Ian J Parrish, Eliot Quataert, Prateek SharmaAbstract:We examine the long-standing cooling flow problem in galaxy clusters with three-dimensional magnetohydrodynamics simulations of isolated clusters including radiative cooling and anisotropic Thermal Conduction along magnetic field lines. The central regions of the intracluster medium (ICM) can have cooling timescales of {approx}200 Myr or shorter-in order to prevent a cooling catastrophe the ICM must be heated by some mechanism such as active galactic nucleus feedback or Thermal Conduction from the Thermal reservoir at large radii. The cores of galaxy clusters are linearly unstable to the heat-flux-driven buoyancy instability (HBI), which significantly changes the thermodynamics of the cluster core. The HBI is a convective, buoyancy-driven instability that rearranges the magnetic field to be preferentially perpendicular to the temperature gradient. For a wide range of parameters, our simulations demonstrate that in the presence of the HBI, the effective radial Thermal conductivity is reduced to {approx}<10% of the full Spitzer conductivity. With this suppression of conductive heating, the cooling catastrophe occurs on a timescale comparable to the central cooling time of the cluster. Thermal Conduction alone is thus unlikely to stabilize clusters with low central entropies and short central cooling timescales. High central entropy clusters have sufficiently long cooling times that Conduction canmore » help stave off the cooling catastrophe for cosmologically interesting timescales.« less
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buoyancy instabilities in galaxy clusters convection due to adiabatic cosmic rays and anisotropic Thermal Conduction
The Astrophysical Journal, 2009Co-Authors: Prateek Sharma, Eliot Quataert, Benjamin D G Chandran, Ian J ParrishAbstract:Using a linear stability analysis and two- and three-dimensional nonlinear simulations, we study the physics of buoyancy instabilities in a combined Thermal and relativistic (cosmic ray) plasma, motivated by the application to clusters of galaxies. We argue that the cosmic-ray diffusion time is likely to be long compared to the buoyancy time on large length scales, so that cosmic rays are effectively adiabatic. If the cosmic-ray pressure p cr is 25% of the Thermal pressure, and the cosmic-ray "entropy" p cr/ρ4/3 (where ρ is the Thermal-plasma density) decreases outward, cosmic rays drive an adiabatic convective instability analogous to Schwarzschild convection in stars. Global simulations of galaxy cluster cores show that this instability saturates by reducing the cosmic-ray entropy gradient and driving efficient convection and turbulent mixing. At larger radii in cluster cores where cosmic-ray pressure is negligible, the Thermal plasma is unstable to the heat-flux-driven buoyancy instability (HBI), a convective instability generated by anisotropic Thermal Conduction and a background conductive heat flux. The HBI saturates by rearranging the magnetic field lines to become largely perpendicular to the local gravitational field; the resulting turbulence also primarily mixes plasma in the perpendicular plane. Cosmic-ray-driven convection and the HBI may contribute to redistributing metals produced by Type Ia supernovae in clusters. Our calculations demonstrate that adiabatic simulations of galaxy clusters can artificially suppress the mixing of Thermal plasma. When anisotropic Thermal Conduction is included, the buoyant response of the Thermal plasma is not governed by the stable entropy gradient, and mixing (driven by mergers, cosmic ray buoyancy, etc.) is more effective. Such mixing may contribute to cosmic rays being distributed throughout the cluster volume.
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anisotropic Thermal Conduction and the cooling flow problem in galaxy clusters
arXiv: Cosmology and Nongalactic Astrophysics, 2009Co-Authors: Ian J Parrish, Eliot Quataert, Prateek SharmaAbstract:We examine the long-standing cooling flow problem in galaxy clusters with 3D MHD simulations of isolated clusters including radiative cooling and anisotropic Thermal Conduction along magnetic field lines. The central regions of the intracluster medium (ICM) can have cooling timescales of ~200 Myr or shorter--in order to prevent a cooling catastrophe the ICM must be heated by some mechanism such as AGN feedback or Thermal Conduction from the Thermal reservoir at large radii. The cores of galaxy clusters are linearly unstable to the heat-flux-driven buoyancy instability (HBI), which significantly changes the thermodynamics of the cluster core. The HBI is a convective, buoyancy-driven instability that rearranges the magnetic field to be preferentially perpendicular to the temperature gradient. For a wide range of parameters, our simulations demonstrate that in the presence of the HBI, the effective radial Thermal conductivity is reduced to less than 10% of the full Spitzer conductivity. With this suppression of conductive heating, the cooling catastrophe occurs on a timescale comparable to the central cooling time of the cluster. Thermal Conduction alone is thus unlikely to stabilize clusters with low central entropies and short central cooling timescales. High central entropy clusters have sufficiently long cooling times that Conduction can help stave off the cooling catastrophe for cosmologically interesting timescales.
Volker Springel - One of the best experts on this subject based on the ideXlab platform.
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enhancing agn efficiency and cool core formation with anisotropic Thermal Conduction
Monthly Notices of the Royal Astronomical Society, 2019Co-Authors: David J Barnes, Volker Springel, Rahul Kannan, Mark Vogelsberger, Christoph Pfrommer, Rainer Weinberger, Ewald Puchwein, Rudiger PakmorAbstract:Understanding how baryonic processes shape the intracluster medium (ICM) is of critical importance to the next generation of galaxy cluster surveys. However, most models of structure formation neglect potentially important physical processes, like anisotropic Thermal Conduction (ATC). In this letter, we explore the impact of ATC on the prevalence of cool-cores (CCs) using 12 pairs of magnetohydrodynamical galaxy cluster simulations, simulated using the IllustrisTNG model with and without ATC. Although the impact of ATC varies from cluster to cluster and with CC criterion, its inclusion produces a systematic shift to larger CC fractions at z = 0 for all CC criteria considered. Additionally, the inclusion of ATC yields a flatter CC fraction redshift evolution, easing the tension with the observed evolution. With ATC included, the energy required for the central black hole to achieve self-regulation is reduced and the gas fraction in the cluster core increases, resulting in larger CC fractions. ATC makes the ICM unstable to perturbations and the increased efficiency of AGN feedback suggests that its inclusion results in a greater level of mixing in the ICM. Therefore, ATC is potentially an important physical process in reproducing the Thermal structure of the ICM.
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increasing black hole feedback induced quenching with anisotropic Thermal Conduction
The Astrophysical Journal, 2017Co-Authors: Rahul Kannan, Volker Springel, Mark Vogelsberger, Christoph Pfrommer, Rainer Weinberger, Lars Hernquist, Ewald Puchwein, Ruediger PakmorAbstract:Feedback from central supermassive black holes is often invoked to explain the low star formation rates (SFRs) in the massive galaxies at the centers of galaxy clusters. However, the detailed physics of the coupling of the injected feedback energy with the intracluster medium (ICM) is still unclear. Using high-resolution magnetohydrodynamic cosmological simulations of galaxy cluster formation, we investigate the role of anisotropic Thermal Conduction in shaping the thermodynamic structure of clusters, and in particular, in modifying the impact of black hole feedback. Stratified anisotropically conducting plasmas are formally always unstable, and thus more prone to mixing, an expectation borne out by our results. The increased mixing efficiently isotropizes the injected feedback energy, which in turn significantly improves the coupling between the feedback energy and the ICM. This facilitates an earlier disruption of the cool-core, reduces the SFR by more than an order of magnitude, and results in earlier quenching despite an overall lower amount of feedback energy injected into the cluster core. With Conduction, the metallicity gradients and dispersions are lowered, aligning them better with observational constraints. These results highlight the important role of Thermal Conduction in establishing and maintaining the quiescence of massive galaxies.
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increasing blackhole feedback induced quenching with anisotropic Thermal Conduction
arXiv: Astrophysics of Galaxies, 2016Co-Authors: Rahul Kannan, Volker Springel, Mark Vogelsberger, Christoph Pfrommer, Rainer Weinberger, Lars Hernquist, Ewald Puchwein, Ruediger PakmorAbstract:Feedback from central supermassive blackholes is often invoked to explain the low star formation rates in massive galaxies at the centers of galaxy clusters. However, the detailed physics of the coupling of the injected feedback energy with the intracluster medium is still unclear. Using high-resolution magnetohydrodynamic cosmological simulations of galaxy cluster formation, we investigate the role of anisotropic Thermal Conduction in shaping the thermodynamic structure of clusters, and, in particular, in modifying the impact of black hole feedback. Stratified anisotropically conducting plasmas are formally always unstable, and thus more prone to mixing, an expectation borne out by our results. The increased mixing efficiently isotropizes the injected feedback energy which in turn significantly improves the coupling between the feedback energy and the intracluster medium. This facilitates an earlier disruption of the cool core, reduces the star formation rate by more than an order of magnitude, and results in earlier quenching despite an overall lower amount of feedback energy injected into the cluster core. With Conduction, the metallicity gradients and dispersions are lowered, aligning them better with observational constraints. These results highlight the important role of Thermal Conduction in establishing and maintaining quiescence of massive galaxies.
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accurately simulating anisotropic Thermal Conduction on a moving mesh
Monthly Notices of the Royal Astronomical Society, 2016Co-Authors: Rahul Kannan, Volker Springel, Rudiger Pakmor, Federico Marinacci, Mark VogelsbergerAbstract:We present a novel implementation of an extremum preserving anisotropic diffusion solver for Thermal Conduction on the unstructured moving Voronoi mesh of the AREPO code. The method relies on splitting the one-sided facet fluxes into normal and oblique components, with the oblique fluxes being limited such that the total flux is both locally conservative and extremum preserving. The approach makes use of harmonic averaging points and a simple, robust interpolation scheme that works well for strong heterogeneous and anisotropic diffusion problems. Moreover, the required discretisation stencil is small. Efficient fully implicit and semi-implicit time integration schemes are also implemented. We perform several numerical tests that evaluate the stability and accuracy of the scheme, including applications such as point explosions with heat Conduction and calculations of convective instabilities in conducting plasmas. The new implementation is suitable for studying important astrophysical phenomena, such as the conductive heat transport in galaxy clusters, the evolution of supernova remnants, or the distribution of heat from blackhole-driven jets into the intracluster medium.
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Thermal Conduction in simulated galaxy clusters
arXiv: Astrophysics, 2004Co-Authors: K Dolag, M Jubelgas, Volker Springel, S Borgani, E RasiaAbstract:We study the formation of clusters of galaxies using high-resolution hydrodynamic cosmological simulations that include the effect of Thermal Conduction with an effective isotropic conductivity of 1/3 the classical Spitzer value. We find that, both for a hot ($T_{\rm ew}\simeq 12$ keV) and several cold ($T_{\rm ew}\simeq 2$ keV) galaxy clusters, the baryonic fraction converted into stars does not change significantly when Thermal Conduction is included. However, the temperature profiles are modified, particularly in our simulated hot system, where an extended isoThermal core is readily formed. As a consequence of heat flowing from the inner regions of the cluster both to its outer parts and into its innermost resolved regions, the entropy profile is altered as well. This effect is almost negligible for the cold cluster, as expected based on the strong temperature dependence of the conductivity. Our results demonstrate that while Thermal Conduction can have a significant influence on the properties of the intra--cluster medium of rich galaxy clusters, it appears unlikely to provide by itself a solution for the overcooling problem in clusters, or to explain the current discrepancies between the observed and simulated properties of the intra--cluster medium.
Kenneth E Goodson - One of the best experts on this subject based on the ideXlab platform.
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anisotropic and inhomogeneous Thermal Conduction in suspended thin film polycrystalline diamond
Journal of Applied Physics, 2016Co-Authors: Aditya Sood, Mehdi Asheghi, Jungwan Cho, Karl D Hobart, Tatyana I Feygelson, B B Pate, David G Cahill, Kenneth E GoodsonAbstract:While there is a great wealth of data for Thermal transport in synthetic diamond, there remains much to be learned about the impacts of grain structure and associated defects and impurities within a few microns of the nucleation region in films grown using chemical vapor deposition. Measurements of the inhomogeneous and anisotropic Thermal conductivity in films thinner than 10 μm have previously been complicated by the presence of the substrate Thermal boundary resistance. Here, we study Thermal Conduction in suspended films of polycrystalline diamond, with thicknesses ranging between 0.5 and 5.6 μm, using time-domain thermoreflectance. Measurements on both sides of the films facilitate extraction of the thickness-dependent in-plane ( κr) and through-plane ( κz) Thermal conductivities in the vicinity of the coalescence and high-quality regions. The columnar grain structure makes the conductivity highly anisotropic, with κz being nearly three to five times as large as κr, a contrast higher than that report...
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quasi ballistic electronic Thermal Conduction in metal inverse opals
Nano Letters, 2016Co-Authors: Michael T Barako, Aditya Sood, Chi Zhang, Junjie Wang, Takashi Kodama, Mehdi Asheghi, Xiaolin Zheng, Paul V Braun, Kenneth E GoodsonAbstract:Porous metals are used in interfacial transport applications that leverage the combination of electrical and/or Thermal conductivity and the large available surface area. As nanomaterials push toward smaller pore sizes to increase the total surface area and reduce diffusion length scales, electron Conduction within the metal scaffold becomes suppressed due to increased surface scattering. Here we observe the transition from diffusive to quasi-ballistic Thermal Conduction using metal inverse opals (IOs), which are metal films that contain a periodic arrangement of interconnected spherical pores. As the material dimensions are reduced from ∼230 nm to ∼23 nm, the Thermal conductivity of copper IOs is reduced by more than 57% due to the increase in surface scattering. In contrast, nickel IOs exhibit diffusive-like Conduction and have a constant Thermal conductivity over this size regime. The quasi-ballistic nature of electron transport at these length scales is modeled considering the inverse opal geometry, s...
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Thermal Conduction in lattice matched superlattices of ingaas inalas
Applied Physics Letters, 2014Co-Authors: Aditya Sood, Mehdi Asheghi, Jeremy A Rowlette, Catherine Caneau, Elah Bozorggrayeli, Kenneth E GoodsonAbstract:Understanding the relative importance of interface scattering and phonon-phonon interactions on Thermal transport in superlattices (SLs) is essential for the simulation of practical devices, such as quantum cascade lasers (QCLs). While several studies have looked at the dependence of the Thermal conductivity of SLs on period thickness, few have systematically examined the effect of varying material thickness ratio. Here, we study through-plane Thermal Conduction in lattice-matched In0.53Ga0.47As/In0.52Al0.48As SLs grown by metalorganic chemical vapor deposition as a function of SL period thickness (4.2 to 8.4 nm) and layer thickness ratio (1:3 to 3:1). Conductivities are measured using time-domain thermoreflectance and vary between 1.21 and 2.31 W m−1 K−1. By studying the trends of the Thermal conductivities for large SL periods, we estimate the bulk conductivities of In0.53Ga0.47As and In0.52Al0.48As to be approximately 5 W m−1 K−1 and 1 W m−1 K−1, respectively, the latter being an order of magnitude low...
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electrical and Thermal Conduction in atomic layer deposition nanobridges down to 7 nm thickness
Nano Letters, 2012Co-Authors: S Yoneoka, Kenneth E Goodson, Takashi Kodama, Jaeho Lee, Matthieu Liger, Gary Yama, Marika Gunji, J Provine, Roger T Howe, Thomas W KennyAbstract:While the literature is rich with data for the electrical behavior of nanotransistors based on semiconductor nanowires and carbon nanotubes, few data are available for ultrascaled metal interconnects that will be demanded by these devices. Atomic layer deposition (ALD), which uses a sequence of self-limiting surface reactions to achieve high-quality nanolayers, provides an unique opportunity to study the limits of electrical and Thermal Conduction in metal interconnects. This work measures and interprets the electrical and Thermal conductivities of free-standing platinum films of thickness 7.3, 9.8, and 12.1 nm in the temperature range from 50 to 320 K. Conductivity data for the 7.3 nm bridge are reduced by 77.8% (electrical) and 66.3% (Thermal) compared to bulk values due to electron scattering at material and grain boundaries. The measurement results indicate that the contribution of phonon Conduction is significant in the total Thermal conductivity of the ALD films.
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Thermal Conduction in aligned carbon nanotube-polymer nanocomposites with high packing density
ACS Nano, 2011Co-Authors: Amy Marie Marconnet, Matthew A. Panzer, Namiko Yamamoto, Brian L. Wardle, Kenneth E GoodsonAbstract:Nanostructured composites containing aligned carbon nanotubes (CNTs) are very promising as interface materials for electronic systems and thermoelectric power generators. We report the first data for the Thermal conductivity of densified, aligned multiwall CNT nanocomposite films for a range of CNT volume fractions. A 1 vol % CNT composite more than doubles the Thermal conductivity of the base polymer. Denser arrays (17 vol % CNTs) enhance the Thermal conductivity by as much as a factor of 18 and there is a nonlinear trend with CNT volume fraction. This article discusses the impact of CNT density on Thermal Conduction considering boundary resistances, increased defect concentrations, and the possibility of suppressed phonon modes in the CNTs.
