Stability of Obliquely Modulated Langmuir Waves in Collisional Plasmas

The effects of collisions and oblique modulation on Langmuir waves are studied. The nonlinear Schrondinger equation for these waves are derived by using the Krylov-Bogoliubov-Mitropolsky method. The collisions damp the envelope of these waves and the obliqueness of the modulation effects the dispersion of the system. The Langmuir waves are found to modulationally stable as in the collisionless and parallel modulation case. However, the width of the envelope hole state of these waves is found to increase due to the oblique modulation.