Nonlinear excitation of vortices at the upper-hybrid layer

It is shown that convective cells can be excited by large-amplitude propagating upper-hybrid waves in a plasma. Using the two-fluid model, a coupled set of differential equations is obtained. A nonlinear dispersion relation for the modulational instability is then derived. This relation is investigated for two parameter regimes and expressions for the growth rates are obtained analytically. The limiting case of a dipole pump field is also considered. The relevance of this work in laser-produced, as well as magnetically confined, plasmas is discussed. (author)