Linear waves and instabilities in thermally anisotropic two-component magnetohydrodynamics

Abstract

The paper analyzes low-frequency waves in a plasma model that is made up of two thermally anisotropic magnetohydrodynamic components, by means of wave-front diagrams, a useful tool that has not attracted the desired attention. The wave-front diagrams of the fast propagating suprathermal mode, besides the usual fast, slow, and Alfvén modes, have been plotted for a variety of situations. These diagrams are used to bring out the physical significance of the anisotropic model vis-à-vis the isotropic model. The question of stability that has been completely ignored so far in the plasma models based on two magnetohydrodynamic components has also been addressed. Analogues of the firehose and mirror instabilities, which are supported by this model, are examined. Their comparison with single-component anisotropic plasma results suggests the possibility of suppressing the mirror instability.

Effect of He++ ions on the propagation of low‐frequency magnetohydrodynamic waves in the magnetosheath

“…The general dispersion relation of the present problem is of eighth order in w. This indicates the existence of eight (four forward and four backward propagating disturbances) wave modes: this is the outcome of the two population MHD model [Parker, 1965;Namikawa et al, 1983;Walker, 1987;Kalra and Ghildyal, 1996;Ghildyal and Kalra, 1997;Lou and Fan, 2003;Kumar and Kalra, 2005]. The mode given by equation (15) is factored out from the rest of the dispersion relation of the problem.…”

“…Both the fluids follow the idealized Ohm's law E + V/c  B = 0 which constrains them to move together in the direction perpendicular to the magnetic field (V x 1 = V x 2 ;V y 1 = V y 2 ) but they are free to have different motion along it (V z 1 6 ¼ V z 2 ). Such a model is applicable in a situation where magnetic field is uniform over a scale that is large compared with the wavelength of perturbation has been used by several authors [Namikawa et al, 1983;Walker, 1987;Ghildyal and Kalra, 1997] in the nonrelativistic framework. The present model is valid for propagation of waves whose characteristic frequency (w) is much less than the gyrofrequencies of the suprathermal He ++ ions composing the relativistic plasma and characteristic spatial scales much larger than the gyroradius of He ++ ions.…”

“…Walker [1987] developed a new hydromagnetic theory based on this concatenated model for describing compressional pulsation with large azimuthal number. Since temperature (pressure) anisotropy is ubiquitous in the space environment, the two-component MHD has been extended to include pressure anisotropy [Kalra and Ghildyal, 1996;Ghildyal and Kalra, 1997] in the nonrelativistic framework.…”

“…Taking g k s = 3, g ? s = 2; s = 1, 2 leads to a dispersion relation of a concatenated system of two anisotropic fluids [Ghildyal and Kalra, 1997].…”

Propagation of waves in a gravitating and rotating anisotropic heat conducting plasma

“…The Chew et al (1956) equations are derived by taking velocity moments of the collisionless Boltzmann transport equation assuming that the thermal heat flow along the field lines can be neglected. Considering the importance of anisotropic pressure plasma, various investigations have been carried out by the authors listed in the references (Gliddon, 1966;Kalra et al, 1970;Kathuria and Kalra, 1973;Chhajlani and Purohit, 1985;Yajima, 1966;Summers, 1978;Ferriere, 2004;Shrauner, 1967;Gedalin, 1993;Gebretsadkan and Kalra, 2002;Ghildyal and Kalra, 1997;Chust and Belmont, 2006), all of them using double adiabatic Chew et al (1956) equations neglecting the heat flux vector.…”