Structure formation by modulational interactions between lower-hybrid and dispersive Alfvén waves

The nonlinear interaction between finite amplitude lower-hybrid (LH) and dispersive Alfvén (DA) waves is considered. For this purpose, a set of equations is derived, which governs the three-dimensional dynamics of nonlinearly coupled LH and DA waves propagating obliquely to an external magnetic field. The interaction between the two wave modes is mediated by the Reynolds stress of the LH waves and the density perturbation associated with the DA wave. Additional terms due to self-interaction nonlinearity of the DA wave are included in order to describe large-amplitude DA waves. Three-wave decay and modulational interactions of the system are analyzed by means of a newly derived nonlinear dispersion relation, which predicts the instability of a finite-amplitude LH pump wave. The fully nonlinear dynamics and the LH wave collapse are studied by solving the governing equations numerically.