{Kinetic simulations to modeling events in space plasmas} / Simulação cinéticas para modelagens de fenômenos em plasma espaciais
AUTOR(ES)
Márcio Augusto Ernesto de Moraes
DATA DE PUBLICAÇÃO
2004
RESUMO
- The purpose of this doctoral thesis is to study some phenomena in space plasma using theoretical models and computer simulation via particles. Firstly, we concentrate on studying the process involving nonlinear interactions among Langmuir, electromagnetic and ion acoustic waves, associated with type III solar radio bursts. Starting from the generalized Zakharov equations, considering two counter propagating Langmuir pump waves with different amplitudes, and excitation of electromagnetic and induced Langmuir waves, we obtain a general dispersion relation. From numerical solutions of the dispersion relation, we found that the stability properties depend on the pump wave numbers and on the ratio of the wave amplitudes of the counter propagating pump waves. The inclusion of a second pump wave allows the simultaneous generation of up and down converted electromagnetic waves. When the second pump wave has different amplitude from the first, convective instability regions appear. The second part of this work consists in the study of instabilities associated with electron nongyrotropy. The Vlasov equation is used to obtain the dispersion relation for the system, considering three species of particles: electrons ( e ) and protons ( p) of background plasma, with distribution function of type 0 ( ) ( , ) e p x f v v⊥ , and a third specie, electrons (b ), with distribution function 0 ( , , ) b x b f v v φ t ⊥ + , that represents phase bunched particles rotating around the ambient magnetic field. We numerically solve this dispersion relation with parameters observed in situ for different types of nongyrotropy. We observe that for determined parameters the nongyrotropy enhances preexisting instabilities. Based on numerical results of the linear analyses, we realized computer simulations via particles, for different types of nongyrotropy. In a general way, the simulations show that the free energy provided by nongyrotropy destabilizes the system, excites new types of wave activities, amplify and stimulate electrostatic and electromagnetic waves.
ASSUNTO(S)
distribuição girotrópica ondas em plasma gyrotropic distribution plasma instabilities plasmas espaciais instabilidades em plasmas space plasmas plasma waves simulação por partículas particle simulations
