Nonlinear Langmuir Wave Modulation in Weakly Magnetized Plasmas

It is assumed that the magnetic field is only important for the ion motion. Both a fluid and a kinetic description of the ions are considered. It is found that the presence of electrostatic ion cyclotron waves, in addition to the ion acoustic waves also found in unmagnetized plasmas, has a strong influence on the modulation stability of plane Langmuir waves. As in the unmagnetized case, kinetic results were found to deviate considerably from those obtained by using a fluid description for the ion dynamics. With particular attention to ionospheric phenomena, the effect is included of the spatially varying electron heating in the amplitude modulated Langmuir wave. For modulations travelling almost perpendicular to the magnetic field, this effect has a profound influence on a modulational instability