Nonlinear mechanism for electromagnetic field generation in modulation-unstable magnetized plasma media

A modulation instability process in a plasma medium is considered in a strong constant magnetic field. The plasmon condensate is modulated not by a low-frequency ionic sound as is usually done, but by the beating of two high-frequency transverse electromagnetic waves propagating along the external magnetic field. Conditions in which aperiodic instability occurs are found and its increment is defined. Instability leads to a decrease of the scale of Langmuir turbulence along the external magnetic field and to the generation of electromagnetic fields. Dissipative property of the medium increases an amplitude threshold of the pumping waves. It is shown that for sufficiently large amplitudes of pumping waves the effect described in the Letter is the defining nonlinear process.