scholarly journals Magnetohydrodynamic spectrum of gravitating plane plasmas with flow

1999 ◽  
Vol 61 (2) ◽  
pp. 221-240 ◽  
Author(s):  
B. van der HOLST ◽  
R. J. NIJBOER ◽  
J. P. GOEDBLOED
Keyword(s):  
Shear Flow ◽  
Spectral Problem ◽  
Critical Values ◽  
Equilibrium Flow ◽  
Local Extrema ◽  
Ideal Magnetohydrodynamic ◽  
The Ideal

The ideal magnetohydrodynamic spectrum of gravitating plane plasmas with equilibrium flow is investigated. Flow makes the spectral problem non-self-adjoint, so that the spectrum can become overstable. The criteria for cluster spectra to appear are derived analytically and both stable and unstable sides of the spectrum are examined numerically. Above certain critical values of the shear flow at the resonant surface, the gravitating interchange modes disappear. However, the local extrema of the continua can then take over the cluster spectrum.

scholarly journals Kinetic ballooning modes in tokamaks and stellarators

2018 ◽  
Vol 84 (6) ◽  
Author(s):  
K. Aleynikova ◽  
A. Zocco ◽  
P. Xanthopoulos ◽  
P. Helander ◽  
C. Nührenberg
Keyword(s):  
Plasma Pressure ◽  
Analytical Prediction ◽  
Ion Temperature ◽  
Ion Temperature Gradient ◽  
Large Pressure ◽  
Equilibrium Configurations ◽  
Mhd Stability ◽  
Ideal Magnetohydrodynamic ◽  
General Geometry ◽  
The Ideal

Kinetic ballooning modes (KBMs) are investigated by means of linear electromagnetic gyrokinetic (GK) simulations in the stellarator Wendelstein 7-X (W7-X), for high-$\unicode[STIX]{x1D6FD}$ plasmas, where $\unicode[STIX]{x1D6FD}$ is the ratio of thermal to magnetic plasma pressure. The analysis shows suppression of ion-temperature-gradient (ITG) and trapped particle modes (TEM) by finite-$\unicode[STIX]{x1D6FD}$ effects and destabilization of KBMs at high $\unicode[STIX]{x1D6FD}$. The results are compared with a generic tokamak case. We show that, for large pressure gradients, the frequency of KBMs evaluated by the GENE code is in agreement with the analytical prediction of the diamagnetic modification of the ideal magnetohydrodynamic limit in W7-X general geometry. Thresholds for destabilization of the KBM are predicted for different W7-X equilibrium configurations. We discuss the relation of these thresholds to the ideal magnetohydrodynamic (MHD) stability properties of the corresponding equilibria.

scholarly journals Planet migration and magnetic torques

2015 ◽  
Vol 11 (A29A) ◽  
pp. 14-18
Author(s):  
A. Strugarek ◽  
A. S. Brun ◽  
S. P. Matt ◽  
V. Reville
Keyword(s):  
Numerical Experiments ◽  
Three Dimensional ◽  
Magnetic Star ◽  
Magnetic Topology ◽  
Global Models ◽  
Planet Migration ◽  
Order Of Magnitude ◽  
Ideal Magnetohydrodynamic ◽  
The Impact ◽  
The Ideal

AbstractThe possibility that magnetic torques may participate in close-in planet migration has recently been postulated. We develop three dimensional global models of magnetic star-planet interaction under the ideal magnetohydrodynamic (MHD) approximation to explore the impact of magnetic topology on the development of magnetic torques. We conduct twin numerical experiments in which only the magnetic topology of the interaction is altered. We find that magnetic torques can vary by roughly an order of magnitude when varying the magnetic topology from an aligned case to an anti-aligned case. Provided that the stellar magnetic field is strong enough, we find that magnetic migration time scales can be as fast as ~100 Myr. Hence, our model supports the idea that magnetic torques may participate in planet migration for some close-in star-planet systems.

Wall stabilization in a collisionless bumpy theta-pinch

1977 ◽  
Vol 18 (2) ◽  
pp. 317-337 ◽  
Author(s):  
George Vahala ◽  
Linda Vahala
Keyword(s):  
Growth Rates ◽  
Normal Mode Analysis ◽  
Upper And Lower Bounds ◽  
Mode Analysis ◽  
Well Posedness ◽  
Theta Pinch ◽  
Pressure Anisotropy ◽  
Special Cases ◽  
Ideal Magnetohydrodynamic ◽  
The Ideal

Finite wavelength guiding centre plasma stability of the bumpy θ-pinch is examined by a normal mode analysis. It is shown that previous bumpy θ-pinch calculations are recoverable as special cases of this analysis. The ideal magnetohydrodynamic and guiding centre plasma growth rates are compared for various pressure anisotropies and for various wavenumbers of the field line bumpiness. The well-posedness conditions on the guiding centre plasma equations are shown to give upper and lower bounds on the permissible pressure anisotropy which corresponds to the Aifvén continuum staying on the stable side of the spectrum and to the particle mirror force not having a singularity. It is also found that the higher azimuthal m ≥ 2 modes have growth rates larger than the m = 1 mode.

Axisymmetric Magnetohydrodynamic Equilibria without a Wall

1993 ◽  
Vol 48 (12) ◽  
pp. 1131-1150
Author(s):  
D. Lortz ◽  
W. Haimerl
Keyword(s):  
Magnetic Field ◽  
Homogeneous Magnetic Field ◽  
Mhd Equations ◽  
External Current ◽  
Flux Function ◽  
Plasma Torus ◽  
Ideal Magnetohydrodynamic ◽  
Axisymmetric Configuration ◽  
A Current ◽  
The Ideal

Abstract Starting from the ideal magnetohydrodynamic (MHD) equations, we consider the following axisymmetric configuration: a current-carrying plasma torus in a homogeneous magnetic field that is aligned parallel to the torus axis. At a certain field strength this configuration is in equilibrium without need of external current singularities such as wires or walls.The magnetic flux function is expanded in small inverse aspect ratio. The geometry of this configuration is completely determined to second order as a function of the profile parameters.

Comment on the paper ‘On the influence of the Hall effect on the spectrum of the ideal magnetohydrodynamic cylindrical pinch’ by U. Schaper

1984 ◽  
Vol 31 (1) ◽  
pp. 173-175 ◽  
Author(s):  
A. Lifshitz ◽  
E. Fedorov ◽  
U. Schaper
Keyword(s):  
Eigenvalue Problem ◽  
Hall Effect ◽  
Distributional Sense ◽  
General Properties ◽  
First Case ◽  
Ideal Magnetohydrodynamic ◽  
Image Position ◽  
The Continuum ◽  
The Ideal

General properties of the eigenvalues of Schaper (1983), concerning the continuum of eigenvalues on p. 7, needs correction. The solutions in the distributional sense of the eigenvalue problem (5.3), will be given for two cases. The first case has been solved by A. Lifshitz and E. Fedorov and concerns continuous eigenvalues. In the second case, the solution for the points of accumulation of discrete eigenvalues is discussed.

scholarly journals DYNAMO EFFECTS IN MAGNETIZED IDEAL PLASMA COSMOLOGIES

2008 ◽  
Vol 23 (11) ◽  
pp. 1697-1710 ◽  
Author(s):  
KOSTAS KLEIDIS ◽  
APOSTOLOS KUIROUKIDIS ◽  
DEMETRIOS PAPADOPOULOS ◽  
LOUKAS VLAHOS
Keyword(s):  
Magnetic Field ◽  
Cosmological Model ◽  
Homogeneous Magnetic Field ◽  
Mhd Equations ◽  
Cosmological Perturbations ◽  
Gravitational Instabilities ◽  
Ideal Magnetohydrodynamic ◽  
The Magnetic Field ◽  
Ideal Plasma ◽  
The Ideal

The excitation of cosmological perturbations in an anisotropic cosmological model and in the presence of a homogeneous magnetic field has been studied, using the ideal magnetohydrodynamic (MHD) equations. In this case, the system of partial differential equations which governs the evolution of the magnetized cosmological perturbations can be solved analytically. Our results verify that fast-magnetosonic modes propagating normal to the magnetic field, are excited. But, what is most important, is that, at late times, the magnetic-induction contrast(δB/B) grows, resulting in the enhancement of the ambient magnetic field. This process can be particularly favored by condensations, formed within the plasma fluid due to gravitational instabilities.

A new decay channel for compressional Alfvén waves in plasmas

2008 ◽  
Vol 74 (1) ◽  
pp. 99-105 ◽  
Author(s):  
G. BRODIN ◽  
P. K. SHUKLA ◽  
L. STENFLO
Keyword(s):  
Decay Channel ◽  
Magnetized Plasma ◽  
Mhd Equations ◽  
Alfven Wave ◽  
Wave Interactions ◽  
Decay Products ◽  
Laboratory Plasmas ◽  
Ideal Magnetohydrodynamic ◽  
Hall Mhd ◽  
The Ideal

AbstractWe present a new efficient wave decay channel involving nonlinear interactions between a compressional Alfvén wave, a kinetic Alfvén wave, and a modified ion sound wave in a magnetized plasma. It is found that the wave coupling strength of the ideal magnetohydrodynamic (MHD) theory is much increased when the effects due to the Hall current are included in a Hall–MHD description of wave–wave interactions. In particular, with a compressional Alfvén pump wave well described by the ideal MHD theory, we find that the growth rate is very high when the decay products have wavelengths of the order of the ion thermal gyroradius or shorter, in which case they must be described by the Hall–MHD equations. The significance of our results to the heating of space and laboratory plasmas as well as for the Solar corona and interstellar media are highlighted.

The large-Larmor-radius Rayleigh–Taylor instability

1998 ◽  
Vol 60 (1) ◽  
pp. 65-68
Author(s):  
M. FAGHIHI ◽  
F. EBRAHIMI
Keyword(s):  
Growth Rate ◽  
Fluid Model ◽  
Taylor Instability ◽  
Larmor Radius ◽  
Rayleigh Taylor Instability ◽  
Magnetohydrodynamic Model ◽  
Ideal Magnetohydrodynamic ◽  
The Ideal

The effect of a large ion Larmor radius on the Rayleigh–Taylor instability is investigated using the Vlasov fluid model. The results are compared with an ideal magnetohydrodynamic model. It is found that this effect reduces the growth rate of the Rayleigh–Taylor instability with respect to the ideal magnetohydrodynamic growth rate.

scholarly journals Phase Structure of Internal Gravity Waves in the Ocean with Shear Flows

2021 ◽  
Vol 37 (4) ◽  
Author(s):  
V. V. Bulatov ◽  
Yu. V. Vladimirov ◽  
I. Yu. Vladimirov ◽  
◽  
◽  
...  
Keyword(s):  
Shear Flow ◽  
Spectral Problem ◽  
Gravity Waves ◽  
Analytical Solutions ◽  
Numerical Solutions ◽  
Internal Gravity Waves ◽  
Buoyancy Frequency ◽  
Flow Profile ◽  
Wave Fields ◽  
Background Shear

Purpose. The description of the internal gravity waves dynamics in the ocean with background fields of shear currents is a very difficult problem even in the linear approximation. The mathematical problem describing wave dynamics is reduced to the analysis of a system of partial differential equations; and while taking into account the vertical and horizontal inhomogeneity, this system of equations does not allow separation of the variables. Application of various approximations makes it possible to construct analytical solutions for the model distributions of buoyancy frequency and background shear ocean currents. The work is aimed at studying dynamics of internal gravity waves in the ocean with the arbitrary and model distributions of density and background shear currents. Methods and Results. The paper represents the numerical and analytical solutions describing the main phase characteristics of the internal gravity wave fields in the stratified ocean of finite depth, both for arbitrary and model distributions of the buoyancy frequency and the background shear currents. The currents are considered to be stationary and horizontally homogeneous on the assumption that the scale of the currents' horizontal and temporal variability is much larger than the characteristic lengths and periods of internal gravity waves. Having been used, the Fourier method permitted to obtain integral representations of the solutions under the Miles – Howard stability condition is fulfilled. To solve the vertical spectral problem, proposed is the algorithm for calculating the main dispersion dependences that determine the phase characteristics of the generated wave fields. The calculations for one real distribution of buoyancy frequency and shear flow profile are represented. Transformation of the dispersion surfaces and phase structures of the internal gravitational waves’ fields is studied depending on the generation parameters. To solve the problem analytically, constant distribution of the buoyancy frequency and linear dependences of the background shear current on depth were used. For the model distribution of the buoyancy and shear flow frequencies, the explicit analytical expressions describing the solutions of the vertical spectral problem were derived. The numerical and asymptotic solutions for the characteristic oceanic parameters were compared. Conclusions. The obtained results show that the asymptotic constructions using the model dependences of the buoyancy frequency and the background shear velocities’ distribution, describe the numerical solutions of the vertical spectral problem to a good degree of accuracy. The model representations, having been applied for hydrological parameters, make it possible to describe qualitatively correctly the main characteristics of internal gravity waves in the ocean with the arbitrary background shear currents.

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