@PhDThesis{SimôesJr:2008:SiCoEm,
author = "Sim{\^o}es Junior, Fernando Jaques Ruiz",
title = "Simula{\c{c}}{\~a}o computacional de emiss{\~o}es
eletromagn{\'e}ticas em plasmas espaciais",
school = "Instituto Nacional de Pesquisas Espaciais (INPE)",
year = "2008",
address = "S{\~a}o Jos{\'e} dos Campos",
month = "2008-06-06",
keywords = "plasma, instabilidade, clima espacial, ondas de plasma,
simula{\c{c}}{\~a}o, plasma, instabilities, space weather,
plasma waves, computer simulation.",
abstract = "Atualmente sabemos que feixes de el{\'e}trons desempenham um
importante papel no mecanismo de emiss{\~o}es de r{\'a}dio que
s{\~a}o comumente observadas na regi{\~a}o acima do arco de
choque terrestre e explos{\~o}es solares tipo II e III. Feixes de
el{\'e}trons que s{\~a}o injetados de volta no vento solar, a
partir do arco de choque terrestre, s{\~a}o uma poss{\'{\i}}vel
fonte das ondas de plasma observadas pelos sat{\'e}lites nesta
regi{\~a}o. Pesquisas recentes sugerem que m{\'u}ltiplos feixes
de el{\'e}trons podem ser injetados em um determinado
per{\'{\i}}odo de tempo. Estes m{\'u}ltiplos feixes tendem a
perder suas identidades individuais para formar um {\'u}nico
feixe. No arco de choque terrestre, observa{\c{c}}{\~o}es
t{\^e}m mostrado que part{\'{\i}}culas energ{\'e}ticas possuem
algum grau de organiza{\c{c}}{\~a}o na fase de giro. Isto
{\'e}, a distribui{\c{c}}{\~a}o de velocidades das
part{\'{\i}}culas no plano perpendicular ao campo magn{\'e}tico
ambiente depende do {\^a}ngulo de giro das part{\'{\i}}culas.
Na primeira parte deste trabalho, resolvemos numericamente a
rela{\c{c}}{\~a}o de dispers{\~a}o n{\~a}o girotr{\'o}pica
utilizando par{\^a}metros de plasma baseados em medidas
observacionais que mostram o agrupamento de fase dos el{\'e}trons
acima do arco de choque terrestre. A import{\^a}ncia da n{\~a}o
girotropia na fun{\c{c}}{\~a}o de distribui{\c{c}}{\~a}o
n{\~a}o est{\'a} completamente compreendida. Para antecipar o
comportamento n{\~a}o girotr{\'o}pico, resolvemos numericamente
a rela{\c{c}}{\~a}o de dispers{\~a}o girotr{\'o}pica paralela
que mostra as poss{\'{\i}}veis regi{\~o}es de acoplamento
quando a n{\~a}o girotropia {\'e} introduzida. Encontramos que a
n{\~a}o girotropia pode fazer o acoplamento dos modos mesmo
quando o sistema {\'e} isotr{\'o}pico. Para uma determinada
n{\~a}o girotropia, a taxa de crescimento apresenta
depend{\^e}ncia na raz{\~a}o entre as freq{\"u}{\^e}ncias de
plasma e ciclotr{\^o}nica, bem como na anisotropia da
temperatura, conhecida como um importante fator na
determina{\c{c}}{\~a}o das instabilidades. Na segunda parte
deste trabalho utilizamos um c{\'o}digo de part{\'{\i}}culas
eletromagn{\'e}tico (KEMPO 1D modificado) para simular dois
feixes de el{\'e}trons que s{\~a}o injetados no plasma em
diferentes instantes de tempo. O primeiro feixe perturba o plasma
ambiente introduzindo ondas de Langmuir atrav{\'e}s de
intera{\c{c}}{\~a}o feixe de plasma. Em seguida, o outro feixe
{\'e} injetado no sistema e interage com o primeiro e com as
ondas de Langmuir para produzir radia{\c{c}}{\~a}o
eletromagn{\'e}tica. As condi{\c{c}}{\~o}es iniciais para os
feixes de el{\'e}trons e para o plasma ambiente s{\~a}o baseadas
em observa{\c{c}}{\~o}es do vento solar e regi{\~a}o do
antechoque terrestre. Em nosso modelo, consideramos que o primeiro
e o segundo feixe de el{\'e}trons, em \$ t=0\$ , ocupam todo o
sistema; isto {\'e} necess{\'a}rio para evitar efeitos
num{\'e}ricos nas grades de contorno e permitir a possibilidade
de utilizarmos o modelo mais simples. Os resultados mostraram que
o primeiro feixe pode produzir harm{\^o}nicos da
freq{\"u}{\^e}ncia de plasma e o segundo feixe modifica a
emiss{\~a}o dos harm{\^o}nicos gerados pelo primeiro feixe. O
segundo feixe de el{\'e}trons interage rapidamente com o intenso
campo el{\'e}trico das ondas de Langmuir fazendo o acoplamento de
fase com o primeiro feixe. Um aumento da energia das componentes
eletromagn{\'e}ticas e da energia cin{\'e}tica tamb{\'e}m
{\'e} observado. ABSTRACT: It is by now well known that electron
beams play an important role in generating radio emissions such as
commonly observed by spacecraft upstream of the Earth's bow shock
and type II and III radio bursts. Electron beams streaming back
from Earth's bow shock into the solar wind have been proposed as a
possible source for the electron plasma waves observed by
spacecraft in the electron foreshock. Recent researche suggest
that multiple electron beams could be injected over a period of
time. They tend to lose their individual identity to form just a
single beam. In Earth's Bow Shock, particle observations have
shown that high energy particles have some degree of gyrophase
organization. Namely, the velocity distribution of the particle
populations in the plane perpendicular to the ambient magnetic
field depends on the gyrophase angle. In the first part of this
work we solve numerically the nongyrotropic parallel dispersion
relation using plasma parameters based on observational data that
show a component of phase-bunched electrons upstream from the
Earth's bow shock. The importance of nongyrotropic electron
distribution in the upstream of the Earth's bow shock is not fully
understood. To anticipate the nongyrotropic behavior, we solve
numerically the gyrotropic parallel dispersion equation that shows
the potential regions of strong coupling when the electron
nongyrotropy is introduced. We find that the nongyrotropy can lead
to a coupling between modes even when the temperature anisotropy
is equal to 1. For a given nongyrotropic angle, the growth rate
presents a dependence on the ratio between electron cyclotron and
electron plasma frequencies as well as on the temperature
anisotropy, known as an important player on determining the growth
rates and the regions were instabilities occur. In the second part
of this thesis we use an electromagnetic PIC code (KEMPO 1D,
modified) to simulate two beams which are injected into a plasma
at different times. The first beam disturbs the background plasma
and generates Langmuir waves by electron beam-plasma interaction.
Subsequently, another beam is inserted in the system and interacts
with the first one and with the Langmuir waves to produce
electromagnetic radiation. The initial conditions for the
background plasma and the electron beams are based on the solar
wind and electron foreshock observations. In our model we consider
that the first and the second beams (for simple and multiples
injections) are, at t=0, fully injected into the system, i.e., the
beam occupies all the system; this is necessary to avoid grid
effects at the boundaries and gives the possibility of using a
simpler model. The results of our simulation show that the first
beam can produce electrostatic harmonics of plasma frequency while
the second beam modifier the harmonics emission that are produced
by the first one. The second beam interacts very fast with the
Langmuir waves due to the strong electric field and the phase
coupling with the first beam. An increasing of electromagnetic and
kinetic energies is also observed.",
committee = "Souza, Jonas Rodrigues de (presidente) and Alves, Maria
Virg{\'{\i}}nia (orientadora) and Bittencourt, Jos{\'e} Augusto
and Dutra, Severino Luiz Guimar{\~a}es and Gaelzer, Rudi",
copyholder = "SID/SCD",
englishtitle = "Computational simulation of electromagnetic emission in space
plasmas",
language = "pt",
pages = "163",
ibi = "6qtX3pFwXQZGivnK2Y/TQSv8",
url = "http://urlib.net/ibi/6qtX3pFwXQZGivnK2Y/TQSv8",
targetfile = "publicacao.pdf",
urlaccessdate = "11 maio 2024"
}