Modulation instability of magnetohydrodynamic waves in a plasma

The interaction between magnetohydrodynamic waves and a plasma at β < < 1 is considered. It is shown that it leads to modulation instability for fast magnetoacoustic waves at a certain level of vibrational energy. A consequence of development of instability is that the particle concentration and energy density of the waves begin to increase in a certain region. Modulation instability of a beam of almost parallel waves may become stabilized in the weakly nonlinear stage. In this case a wave channel with a high plasma density is formed in which the waves are contained as a result of refraction. In the case of an isotropic wave distribution compression of the plasma may proceed until the vibration and particle energies become equal to that of the stationary magnetic field. The feasibility of observing modulation instability of fast magnetoacoustic waves under natural conditions is discussed