Modulational instability and collapse of plasma waves in a magnetic field

The effect of finite filament length on the modulational instability and collapse of plasma waves propagating in a weak or moderate magnetic field (omega-H much less than omega-p) perpendicular to the initial oscillatory electric field is investigated analytically. Self-similar solutions are obtained, and regions of both aperiodic and oscillatory instability are defined on the plane of the vectors k0 and H0 in zeta space. The maximum growth rates are determined, and the directions of growth for both types of instability are shown to be significantly different from the direction of the original electric field, suggesting that the primary nonlinear process is angular pumping of energy in the direction of the magnetic field, ending in longitudinal Langmuir collapse.