WAVE COLLAPSE AT THE LOWER-HYBRID RESONANCE

The modulational instability and collapse of waves in the vicinity of the lower-hybrid resonance including both magnetosonic and lower-hybri d waves are investigated by analytical and numerical methods. The mech anism leading to the modulational instability is the nonlinear couplin g of lower-hybrid waves with the much lower-frequency quasineutral den sity perturbations via the ponderomotive force. The result is a filame ntation of the high-frequency field producing elongated, cigar-shaped nonlinear wave packets aligned along the magnetic field with the plasm a expelled outside (cavities). The analytical self-similar solutions d escribing cavity collapse are obtained and compared with the results o f numerical simulation for both two-and three-dimensional cavity geome tries. It is shown that in three-dimensional solutions the transverse, with respect to the magnetic field, contraction remains prevailing. T he possibility of ion acceleration as the result of the lower-hybrid c ollapse is discussed and detailed comparison is made with the observat ions of the phenomena in the auroral ionosphere.