2016/10/19 by Karen Pommois, Francesco Valentini, Oreste Pezzi +1 · 1 citation
Physics and Astronomy · #Amplitude #Dust and Plasma Wave Phenomena #Electric field #Electron #Excitation #Ionosphere and magnetosphere dynamics #Magnetic confinement fusion research #Nonlinear system #Phase space #Plasma #Vlasov equation #Vortex #Wavenumber #physics.plasm-ph
paper · pdf · doi:10.1063/1.4973829
arxiv created 2016/10/19 · openalex publication_date 2017/01/01 · arxiv updated 2017/08/02 · openalex created_date 2019/06/27 · openalex updated_date 2026/08/05
Eulerian simulations of the Vlasov-Poisson equations have been employed to analyze the excitation of slow electrostatic fluctuations (with phase speed close to the electron thermal speed), due to a beam-plasma interaction, and their propagation in linear and nonlinear regimes. In 1968, O'Neil and Malmberg [Phys. Fluids 11, 1754 (1968)] dubbed these waves “beam modes.” In the present paper, previous analytical results on the beam modes in both linear and nonlinear regimes have been revisited numerically, pointing out that, when an electron beam is launched in a plasma of Maxwellian electrons and motionless protons and this initial equilibrium is perturbed by a monochromatic density disturbance, the electric field amplitude grows exponentially in time and then undergoes nonlinear saturation, associated with the kinetic effects of particle trapping and phase space vortex generation. Moreover, new numerical results give evidence that, when the initial density perturbation is setup in the form of a low amplitude random phase noise, the whole Fourier spectrum of wavenumbers is excited. As a result, the electric field profile appears as a train of isolated pulses, each of them being associated with a phase space vortex in the electron distribution function. At later times, these vortical structures tend to merge and, correspondingly, the electric pulses collapse, showing the tendency towards a time asymptotic configuration characterized by the appearance of electric soliton-like pulses. This dynamical evolution is driven by purely kinetic processes, possibly at work in many space and laboratory plasma environments.