Journal of Plasma Physics

Alfvén-wave filamentation

S. CHAMPEAUX a1, T. PASSOT a1 and P. L. SULEM a1
a1 CNRS UMR 6529, Observatoire de la Côte d'Azur, BP 4229, 06304 Nice Cedex 4, France


Transverse focusing or filamentation of weakly nonlinear Alfvén waves propagating in a dispersive medium is studied using an amplitude-equation formalism. Special attention is devoted to the small-β regime, where kinetic effects are weak and Alfvén-wave trains are unstable to convective filamentation. It is shown that, according to their initial duration, focusing wave packets can collapse in a finite distance or, conversely, the focusing can be arrested by the development of magnetosonic waves, which in both cases may lead to the formation of sharp acoustic fronts. This effect, which dominates the usual longitudinal steepening, provides an efficient mechanism to heat the plasma without requiring large-amplitude waves. It can significantly contribute to the acceleration of the solar wind.

(Received October 14 1996)
(Revised December 30 1996)