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J.d. Huba - One of the best experts on this subject based on the ideXlab platform.
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The Kelvin‐Helmholtz instability: Finite Larmor Radius magnetohydrodynamics
Geophysical Research Letters, 1996Co-Authors: J.d. HubaAbstract:A preliminary theoretical and computational study of the Kelvin-Helmholtz instability in an inhomogeneous plasma is presented using finite Larmor Radius magnetohydrodynamic (FLR MHD) theory. We show that FLR effects (1) can increase or decrease the linear growth rate, (2) cause the nonlinear evolution to be asymmetric, and (3) allow plasma ‘blobs’ to detach from the boundary layer. The asymmetric growth and nonlinear evolution depend on the sign of B · Ω where B is the magnetic field and Ω = ▽ × V is the vorticity. The simulation results are qualitatively consistent with the hybrid simulations of Thomas and Winske (1991, 1993) and Thomas (1995). These results suggest that FLR MHD can capture important physical processes on length scales approaching the ion Larmor Radius.
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the kelvin helmholtz instability finite Larmor Radius magnetohydrodynamics
Geophysical Research Letters, 1996Co-Authors: J.d. HubaAbstract:A preliminary theoretical and computational study of the Kelvin-Helmholtz instability in an inhomogeneous plasma is presented using finite Larmor Radius magnetohydrodynamic (FLR MHD) theory. We show that FLR effects (1) can increase or decrease the linear growth rate, (2) cause the nonlinear evolution to be asymmetric, and (3) allow plasma ‘blobs’ to detach from the boundary layer. The asymmetric growth and nonlinear evolution depend on the sign of B · Ω where B is the magnetic field and Ω = ▽ × V is the vorticity. The simulation results are qualitatively consistent with the hybrid simulations of Thomas and Winske (1991, 1993) and Thomas (1995). These results suggest that FLR MHD can capture important physical processes on length scales approaching the ion Larmor Radius.
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finite Larmor Radius magnetohydrodynamics of the rayleigh taylor instability
Physics of Plasmas, 1996Co-Authors: J.d. HubaAbstract:The evolution of the Rayleigh–Taylor instability is studied using finite Larmor Radius (FLR) magnetohydrodynamic (MHD) theory. Finite Larmor Radius effects are introduced in the momentum equation through an anisotropic ion stress tensor. Roberts and Taylor [Phys. Rev. Lett. 3, 197 (1962)], using fluid theory, demonstrated that FLR effects can stabilize the Rayleigh–Taylor instability in the short‐wavelength limit (kLn≫1, where k is the wave number and Ln is the density gradient scale length). In this paper a linear mode equation is derived that is valid for arbitrary kLn. Analytic solutions are presented in both the short‐wavelength (kLn≫1) and long‐wavelength (kLn≪1) regimes, and numerical solutions are presented for the intermediate regime (kLn∼1). The long‐wavelength modes are shown to be the most difficult to stabilize. More important, the nonlinear evolution of the Rayleigh–Taylor instability is studied using a newly developed two‐dimensional (2‐D) FLR MHD code. The FLR effects are shown to be a stab...
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Finite Larmor Radius magnetohydrodynamics of the Rayleigh–Taylor instability
Physics of Plasmas, 1996Co-Authors: J.d. HubaAbstract:The evolution of the Rayleigh–Taylor instability is studied using finite Larmor Radius (FLR) magnetohydrodynamic (MHD) theory. Finite Larmor Radius effects are introduced in the momentum equation through an anisotropic ion stress tensor. Roberts and Taylor [Phys. Rev. Lett. 3, 197 (1962)], using fluid theory, demonstrated that FLR effects can stabilize the Rayleigh–Taylor instability in the short‐wavelength limit (kLn≫1, where k is the wave number and Ln is the density gradient scale length). In this paper a linear mode equation is derived that is valid for arbitrary kLn. Analytic solutions are presented in both the short‐wavelength (kLn≫1) and long‐wavelength (kLn≪1) regimes, and numerical solutions are presented for the intermediate regime (kLn∼1). The long‐wavelength modes are shown to be the most difficult to stabilize. More important, the nonlinear evolution of the Rayleigh–Taylor instability is studied using a newly developed two‐dimensional (2‐D) FLR MHD code. The FLR effects are shown to be a stab...
Sunil - One of the best experts on this subject based on the ideXlab platform.
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Finite Larmor Radius effect on thermosolutal instability of a compressible Hall plasma in porous medium
Physics of Plasmas, 1999Co-Authors: SunilAbstract:The thermosolutal instability of a compressible plasma in porous medium is considered in the presence of a uniform vertical magnetic field to include the finite Larmor Radius and Hall effects. The dispersion relation has been obtained. The system is found to be stable for (Cp/g)β 1, which were nonexistent in their absence. For the stationary convection, the effect of compressibility is found to postpone the onset of thermosolutal instability. The effect of stable solute gradient, finite Larmor Radius, Hall currents, magnetic field, and medium permeability have been investigated analytically.
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Finite Larmor Radius effect on thermosolutal instability of a plasma in porous medium
Czechoslovak Journal of Physics, 1994Co-Authors: R. C. Sharma, SunilAbstract:The thermosolutal instability of a plasma in porous medium is considered in the presence of finite Larmor Radius effect. The finite Larmor Radius, stable solute gradient and magnetic field introduce oscillatory modes in the systems which were nonexistent in their absence. For stationary convection, the finite Larmor Radius and stable solute gradient have stabilizing effects on the thermosolutal instability in porous medium. In presence of finite Larmor Radius effect, the medium permeability has a destabilizing (or stabilizing) effect and the magnetic field has a stabilizing (or destabilizing) effect under certain condition whereas in the absence of finite Larmor Radius effect, the medium permeability and the magnetic field have destabilizing and stabilizing effects, respectively, on thermosolutal instability of a plasma in porous medium. The sufficient conditions for nonexistence of overstability are obtained.
Jan Scheffel - One of the best experts on this subject based on the ideXlab platform.
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Linear stability of the collisionless, large Larmor Radius Z-pinch
Physics of Plasmas, 1997Co-Authors: Peter George Fisher Russell, Tony Arber, Michael Coppins, Jan ScheffelAbstract:The Vlasov fluid model is used to study the m=0 and m=1 internal and free boundary modes in a collisionless, large Larmor Radius Z pinch. Two methods (initial value and variational) are employed, and give good agreement. The growth rate can be reduced from its zero Larmor Radius value by a factor of up to 10 for m=1, and up to 3 for m=0. Stability thresholds and the role of resonant ions are discussed.
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Recent progress on large Larmor Radius theory
The fourth international conference on dense z-pinches, 1997Co-Authors: Michael Coppins, Tony Arber, Peter George Fisher Russell, Jan ScheffelAbstract:An overview of theoretical work on large Larmor Radius stability of the z-pinch is presented, highlighting two recent innovations. Firstly, finite electron temperature has been included for the linear m=0 instability. Compared to the usual cold electron case, growth rates are increased and are closer to those of ideal MHD. Secondly, a 2-D hybrid code has been written to study the non-linear development of the m=0 instability. First results provide no evidence of instability saturation.
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Large Larmor Radius stability of the z pinch.
Physical review letters, 1994Co-Authors: Tony Arber, Michael Coppins, Jan ScheffelAbstract:The linear [ital m]=0 stability of the [ital z] pinch in the collisionless, large ion Larmor Radius regime is examined using the Vlasov fluid model. The results reveal a strong equilibrium dependence. The uniform current density equilibrium shows a reduction in growth rate when the average ion Larmor Radius is about one-fifth of the pinch Radius. However, finite Larmor Radius effects cannot in themselves produce a stabilized [ital z] pinch.
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Linear Stability of the Large Larmor Radius Z-Pinch
AIP Conference Proceedings, 1994Co-Authors: Jan Scheffel, Tony Arber, Michael CoppinsAbstract:For the first time, calculations of large Larmor Radius (LLR) effects on the linear stability of realistic Z‐pinch equilibria have been performed. The fixed boundary m=0 instability of the pure Z‐pinch (no external magnetic field) is considered (free‐boundary and m=1 modes are presently under study). We use the Vlasov‐Fluid model, where ions are treated fully kinetically and electrons are modelled as a cold, massless fluid. Stability is found to be remarkably sensitive to equilibrium profiles. A flat current equilibrium is increasingly stabilized (smaller growth rate) by LLR effects as the normalized average Larmor Radius e is increased to about 0.1. Complete stabilization cannot be obtained. For larger values of e the growth rate increases to reach above the small Larmor Radius value when e≈0.3. The Bennett equilibrium, however, is increasingly destabilized as e increases.
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Boundary Larmor Radius effect on electrostatic waves
Physics of Fluids B: Plasma Physics, 1991Co-Authors: Jan ScheffelAbstract:The linearized Vlasov–Poisson equations, which combine to an integrodifferential equation for the perturbed electric potential, are used to investigate the effect of finite plasma size on the stability of electrostatic waves in a homogeneous plasma slab. The distortion of the gyromotion of the particles at the plasma boundary influences wave stability, a phenomenon termed the boundary Larmor Radius (BLR) effect. The integrodifferential equation, treated as an eigenvalue problem, is discretized into a matrix dispersion equation by use of the Galerkin method and is then solved numerically. It is found that the ion Bernstein wave, which is undamped in an infinite homogeneous plasma, now becomes damped with a maximum damping rate of 0.35 ωci at rG/L (ion Larmor Radius over wall distance)≊0.15. In general, the damping is less pronounced at shorter perpendicular wavelengths. It implies a necessity to take into account the BLR effect in the kinetic stability studies for sufficiently large ion Larmor Radius in co...
O. A. Pokhotelov - One of the best experts on this subject based on the ideXlab platform.
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Finite ion Larmor Radius effects in magnetic curvature-driven Rayleigh-Taylor instability
2012Co-Authors: O. G. Onishchenko, O. A. Pokhotelov, Lennart Stenflo, P. K. ShuklaAbstract:Incomplete finite ion Larmor Radius stabilization of the magnetic Rayleigh-Taylor (RT)instability is investigated. In contrast to the previous studies the effects of both the gravity and magnetic field curvature are taken into account. New model hydrodynamic equations describing nonlinear flute waves with arbitrary spatial scales have been derived. Particular attention is paid to the waves with spatial scales of the order of the ion Larmor Radius. In the linear approximation a Fourier transform of these equations yields a generalized dispersion relation for flute waves. The condition for gravity and magnetic curvature at which the instability cannot be stabilized by the finite ion Larmor Radius effects is found. It is shown that in the absence of the magnetic curvature the complete stabilization arises due to the cancellation of gravitational and diamagnetic drifts. However, when the magnetic curvature drift is taken into account this synchronization is violated and the RT instability is stabilized at more complex conditions. Furthermore, the dependence of the instability growth rate on the equilibrium plasma parameters is investigated.
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the magnetic rayleigh taylor instability and flute waves at the ion Larmor Radius scales
Physics of Plasmas, 2011Co-Authors: O. G. Onishchenko, O. A. Pokhotelov, Lennart Stenflo, P. K. ShuklaAbstract:The theory of flute waves (with arbitrary spatial scales compared to the ion Larmor Radius) driven by the Rayleigh-Taylor instability (RTI) is developed. Both the kinetic and hydrodynamic models are considered. In this way we have extended the previous analysis of RTI carried out in the long wavelength limit. It is found that complete finite ion Larmor Radius stabilization is absent when the ion diamagnetic velocity attains the ion gravitation drift velocity. The hydrodynamic approach allowed us to deduce a new set of nonlinear equations for flute waves with arbitrary spatial scales. It is shown that the previously deduced equations are inadequate when the wavelength becomes of the order of the ion Larmor Radius. In the linear limit a Fourier transform of these equations yields the dispersion relation which in the so-called Pade approximation corresponds to the results of the fully kinetic treatment. The development of such a theory gives us enough grounds for an adequate description of the RTI stabilization by the finite ion Larmor Radius effect.
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The magnetic Rayleigh–Taylor instability and flute waves at the ion Larmor Radius scales
Physics of Plasmas, 2011Co-Authors: O. G. Onishchenko, O. A. Pokhotelov, Lennart Stenflo, P. K. ShuklaAbstract:The theory of flute waves (with arbitrary spatial scales compared to the ion Larmor Radius) driven by the Rayleigh-Taylor instability (RTI) is developed. Both the kinetic and hydrodynamic models are considered. In this way we have extended the previous analysis of RTI carried out in the long wavelength limit. It is found that complete finite ion Larmor Radius stabilization is absent when the ion diamagnetic velocity attains the ion gravitation drift velocity. The hydrodynamic approach allowed us to deduce a new set of nonlinear equations for flute waves with arbitrary spatial scales. It is shown that the previously deduced equations are inadequate when the wavelength becomes of the order of the ion Larmor Radius. In the linear limit a Fourier transform of these equations yields the dispersion relation which in the so-called Pade approximation corresponds to the results of the fully kinetic treatment. The development of such a theory gives us enough grounds for an adequate description of the RTI stabilization by the finite ion Larmor Radius effect.
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Drift-Alfvén vortices at the ion Larmor Radius scale
Physics of Plasmas, 2008Co-Authors: O. G. Onishchenko, Vladimir Krasnoselskikh, O. A. PokhotelovAbstract:The theory of nonlinear drift-Alfven waves with the spatial scales comparable to the ion Larmor Radius is developed. It is shown that the set of equations describing the nonlinear dynamics of drift-Alfven waves in a quasistationary regime admits a solution in the form of a solitary dipole vortex. The vortex structures propagating perpendicular to the ambient magnetic field faster than the diamagnetic ion drift velocity possess spatial scales larger than the ion Larmor Radius, and vice versa. The variation of the vortex impedance and spatial scale as the function of the vortex velocity is analyzed. It is shown that incorporation of the finite electron temperature effects results in the appearance of a minimum in the dependence of the vortex impedance on the vortex velocity. This leads to the existence of the vortex structures with the smallest impedance. These structures are probably the most favorable energetically and can easily be excited in space plasmas. The relevance of theoretical results obtained to the Cluster observations in the magnetospheric cusp and magnetosheath is stressed.
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Mirror instability including finite Larmor Radius effects
Advances in Space Research, 2006Co-Authors: O. A. Pokhotelov, Roald Sagdeev, Michael A. Balikhin, Rudolf A. TreumannAbstract:Abstract We present a fully kinetic theory of the magnetic mirror instability accounting for finite ion Larmor Radius (FLR) effects. Including FLR effects leads to a substantial modification of both the instability growth rate and the instability threshold. For wavelengths the order of the ion Larmor Radius the effective elasticity of the magnetic field lines increases substantially. The latter results in an increase of the mirror instability threshold. A compact analytical expression is obtained for the growth rate of the fastest growing mode in the fully kinetic regime. In the presence of FLR effects, a non-coplanar component of the magnetic field perturbation is generated which is occasionally observed in satellite data.
P. K. Shukla - One of the best experts on this subject based on the ideXlab platform.
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Finite ion Larmor Radius effects in magnetic curvature-driven Rayleigh-Taylor instability
2012Co-Authors: O. G. Onishchenko, O. A. Pokhotelov, Lennart Stenflo, P. K. ShuklaAbstract:Incomplete finite ion Larmor Radius stabilization of the magnetic Rayleigh-Taylor (RT)instability is investigated. In contrast to the previous studies the effects of both the gravity and magnetic field curvature are taken into account. New model hydrodynamic equations describing nonlinear flute waves with arbitrary spatial scales have been derived. Particular attention is paid to the waves with spatial scales of the order of the ion Larmor Radius. In the linear approximation a Fourier transform of these equations yields a generalized dispersion relation for flute waves. The condition for gravity and magnetic curvature at which the instability cannot be stabilized by the finite ion Larmor Radius effects is found. It is shown that in the absence of the magnetic curvature the complete stabilization arises due to the cancellation of gravitational and diamagnetic drifts. However, when the magnetic curvature drift is taken into account this synchronization is violated and the RT instability is stabilized at more complex conditions. Furthermore, the dependence of the instability growth rate on the equilibrium plasma parameters is investigated.
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the magnetic rayleigh taylor instability and flute waves at the ion Larmor Radius scales
Physics of Plasmas, 2011Co-Authors: O. G. Onishchenko, O. A. Pokhotelov, Lennart Stenflo, P. K. ShuklaAbstract:The theory of flute waves (with arbitrary spatial scales compared to the ion Larmor Radius) driven by the Rayleigh-Taylor instability (RTI) is developed. Both the kinetic and hydrodynamic models are considered. In this way we have extended the previous analysis of RTI carried out in the long wavelength limit. It is found that complete finite ion Larmor Radius stabilization is absent when the ion diamagnetic velocity attains the ion gravitation drift velocity. The hydrodynamic approach allowed us to deduce a new set of nonlinear equations for flute waves with arbitrary spatial scales. It is shown that the previously deduced equations are inadequate when the wavelength becomes of the order of the ion Larmor Radius. In the linear limit a Fourier transform of these equations yields the dispersion relation which in the so-called Pade approximation corresponds to the results of the fully kinetic treatment. The development of such a theory gives us enough grounds for an adequate description of the RTI stabilization by the finite ion Larmor Radius effect.
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The magnetic Rayleigh–Taylor instability and flute waves at the ion Larmor Radius scales
Physics of Plasmas, 2011Co-Authors: O. G. Onishchenko, O. A. Pokhotelov, Lennart Stenflo, P. K. ShuklaAbstract:The theory of flute waves (with arbitrary spatial scales compared to the ion Larmor Radius) driven by the Rayleigh-Taylor instability (RTI) is developed. Both the kinetic and hydrodynamic models are considered. In this way we have extended the previous analysis of RTI carried out in the long wavelength limit. It is found that complete finite ion Larmor Radius stabilization is absent when the ion diamagnetic velocity attains the ion gravitation drift velocity. The hydrodynamic approach allowed us to deduce a new set of nonlinear equations for flute waves with arbitrary spatial scales. It is shown that the previously deduced equations are inadequate when the wavelength becomes of the order of the ion Larmor Radius. In the linear limit a Fourier transform of these equations yields the dispersion relation which in the so-called Pade approximation corresponds to the results of the fully kinetic treatment. The development of such a theory gives us enough grounds for an adequate description of the RTI stabilization by the finite ion Larmor Radius effect.
