Wave Motion in a Plasma with Anisotropic Pressure

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Abstract
The moment equations, neglecting the heat‐flow tensor, have been used to study the wave propagation in a plasma consisting of electrons and singly charged ions, in a magnetic field, with anisotropic pressure tensors for both components. Two cases of wave propagation along the magnetic field and perpendicular to it have been worked out separately. In the first case of propagation along the magnetic field, the waves separate into a pure longitudinal and a pure transverse wave, the second of these only being affected by the anisotropy of the pressure tensor. Conditions are deduced under which the anisotropy of the pressure tensor can alter the propagation conditions of the waves. Attention is also given to the possibility that it can give rise to an instability. One important result which follows for magnetohydrodynamic waves is that an anisotropy in the electron pressure can give rise to an instability of the Alfvén waves. In the other case of the propagation across the field, the waves separate into a pure transverse wave and a wave which represents a combined longitudinal and transverse wave. The second of these is unaffected by the anisotropy of the pressure tensor. For the pure transverse wave, conditions are obtained under which instability can arise.