NONLINEAR EFFECTS FOR FMS WAVES PROPAGATING IN MAGNETIZED PLASMA

Non linear effects for small-amplitude fast magnetosonic (FMS) waves having a close angular distribution, which are excited in magnetized plasma with beta = 4pinT/B2 << 1 and omega < omega(B) = eB/Mc, klambda(D) << 1 where lambda(D)2 is the dispersive length, and which propagate near the cone of theta = k, B = arctan(M/m)1/2, are studied. It is shown that, in this case, the evolution of three-dimensional FMS waves is described by the Kadomtsev-Petviashvili (KP) equation generalized by introducing a next-order dispersion correction which plays a major role. For an FMS wave beam propagating in plasma the problems of stability and evolution including initial subfocusing, nonlinear 'saturation' and defocusing stages are investigated in detail. It is shown that, unlike the usual KP equation model, self-focusing is not observed even if the dispersion for small k is positive; nonlinear stationary propagation, as a result of nonlinear stabilization of the FMS waves beam, may be observed.