Effect of collisions on wave motions in a plasma with anisotropic pressure

Abstract

The development with time of small-amplitude oscillations, having harmonic spatial dependence, in a magnetoactive plasma is examined with the aid of moment equations. The plasma, which is assumed to be homogeneous and unbounded, has an initial anisotropic distribution of pressure. Neglecting the motion of the ions, we consider in detail the effect of collisions on the further development of the system for the propagation vector along or perpendicular to the magnetic field. For the collisionless case we obtain the dispersion relations derived by Jaggi. For the case of weak collisions explicit expressions for the damping and phase shift coefficients are evaluated. It is found that, for longitudinal propagation along the magnetic field, the collisional damping decreases or increases according to whether the perpendicular pressure is greater or less than the longitudinal pressure. High-frequency transverse waves may exhibit a collision-induced instability if the pressure anisotropy is large and of the correct sign. For extremely-high-pressure relaxation frequencies we recover the ordinary dispersion relations, in which only the momentum relaxation frequency contributes to the damping of the wave.