Electron beam-plasma interaction: Linear theory and Vlasov-Poisson simulations

The problem of a weak ( n b ∕ n e ∼ 10 − 3 ) electron beam interaction with plasma is investigated by means of linear dispersion theory and electrostatic Vlasov simulations. In the case of a warm electron beam only Langmuir-type modes in a finite wavelength band are excited. Cold beams undergo rapid heating, after which the long-wavelength Langmuir and electron-acoustic modes are damped. As the waves decelerate and heat the beam, new modes with larger wave numbers and smaller phase velocities are excited, while the fastest-growing modes saturate at a finite level. The superposition of these modes with frequencies near electron plasma frequency ω p e and broad k spectrum results in long quasiregular wave packets. The wave packets propagate slowly with group velocities typically 30 times smaller than the phase velocities and are weakly damped by the background electrons.