ALFVEN-WAVE PHASE MIXING AS A SOURCE OF FAST MAGNETOSONIC WAVES

The nonlinear excitation of fast magnetosonic waves by phase mixing Al fven waves in a cold plasma with a smooth inhomogeneity of density acr oss a uniform magnetic field is considered. If initially fast waves ar e absent from the system, then nonlinearity leads to their excitation by transversal gradients in the Alfven wave. The efficiency of the non linear Alfven-fast magnetosonic wave coupling is strongly increased by the inhomogeneity of the medium. The fast waves, permanently generate d by Alfven wave phase mixing, are refracted from the region with tran sversal gradients of the Alfven speed. This nonlinear process suggests a mechanism of indirect plasma heating by phase mixing through the ex citation of obliquely propagating fast waves.