A teoria da turbulência fraca para oscilações eletrostáticas em plasmas com feixes de alta intensidade

Abstract

The interaction between an electron beam and the plasma that surrounds it is of fundamental importance in physics of plasmas, both in the study of laboratory plasmas and in space and astrophysical plasmas. A possible approach to describe this type of interaction is the Weak Turbulence Theory, which consists of a formulation used to describe the interaction between particles and waves of a beam-plasma system. This theory is strictly valid when the plasma is weakly unstable, which for a beam-plasma system amounts to consider beams of low intensity. The present work proposes to extend the validity of Weak Turbulence Theory to describe phenomena involving beams of higher intensity, which are frequently observed in realistic systems and are not adequately described by the usual theory. Specifically, the dispersion relation of a beam-plasma system is modeled accordingly to its numerical solution, and incorporated in the calculation of the quasilinear terms and three-wave coupling nonlinear terms. The results of the temporal evolution of waves and particles obtained using the Weak Turbulence Theory approach for high intensity beams show that the behavior of this system with high intensity beams follows the behavior of the system with low intensity beams. The results found may be explained by the fact that, although the usual theory considers wave coupling of two different wave modes, whereas the present study considers the existence of a unique mode, the dispersion relation of the mode considered shows a low frequency range as well as a high frequency range, which ultimately play the role of ion-sonic and Langmuir waves, respectively. The results found support the cosistency of Weak Turbulence Theory, in the sense that in both cases involving low or high beam intensity, wave and particle behavior is alike.