Langmuir Oscillations

Abstract

Langmuir oscillations, (also called Langmuir waves or electron plasma waves), constitute an important phenomenon taking place in a nonmag-netized or weakly magnetized plasma, and have applications to both astrophysical situations such as solar radio emission (ter Haar and Tsytovich 1975, Gurnett, Maggs, Gallagher, Kurth, and Scarf 1981, Gold-manl983, 1984) and laboratory experiments (Wong and Cheung 1984, Cheung and Wong 1985). Application to the ionosphere is considered by Rose, Dubois, Russel, and Bezzerides (1991). A review is found in Robinson (1997). Modulational instability leads to the formation of regions of lower plasma density (cavities) where high-frequency oscillations of the electric field are trapped. The nonlinear evolution leads to the collapse of the cavities and to a strong amplification of the oscillation amplitude. This provides an effective mechanism for the dissipation of long-wavelength plasma waves. Collapse thus plays a central role in the dynamics of Langmuir turbulence, and strong attention has been paid to this problem after Zakharov (1972) derived the equations governing the coupled dynamics of the electric-field amplitude and of the low-frequency density fluctuations of the ions (see also Zakharov 1984, Rubenchik, Sagdeev, and Zakharov 1985). The energy absorption that could occur in the postcollapse evolution of the cavities as the result of the drawing of new Langmuir waves into them is considered by Malkin (1991).