Nonlinear development of weak beam-plasma instability

Nonlinear interactions of tenuous electron beam, background, unmagnetized p lasma, and self-consistently generated Langmuir and ion-sound waves are ana lyzed in the framework of plasma weak turbulence kinetic theory. Full numer ical solutions of the complete weak turbulence equations are obtained for t he first time, which show the familiar plateau formation in the electron be am distribution and concomitant quasi-saturation of primary Langmuir waves, followed by fully nonlinear processes which include three-wave decay and i nduced-scattering processes. A detailed analysis reveals that the scatterin g off ions is an important nonlinear process which leads to prominent backs cattered and long-wavelength Langmuir wave components. However, it is found that the decay process is also important, and that the nonlinear developme nt of weak Langmuir turbulence critically depends on the initial conditions . Special attention is paid to the electron-to-ion temperature ratio, T-e/T -i, and the initial perturbation level. It is found that higher values of T -e/T-i promote the generation of backscattered Langmuir wave component, and that a higher initial wave intensity suppresses the backscattered componen t while significantly enhancing the long-wavelength Langmuir wave component . (C) 2001 American Institute of Physics.