Plasma Instabilities in Ring and Bi-Maxwellian Electron Distributions
Typ
Examensarbete för masterexamen
Program
Publicerad
2021
Författare
Johansson, Albert
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
Kinetic plasma instabilities affect a wide range of plasmas, from the small scales
of laser-generated plasmas, up to the very largest scales of astrophysical plasmas.
These instabilities depend on details of the velocity distribution of the particles.
However, it is experimentally challenging to initialize the system with a
sufficiently accurately known distribution function, that can be used for quantitative
studies of kinetic instabilities. Recent results have shown the possibility
of tailoring the velocity distribution through rapid ionization in laser-generated
plasmas. Examples of such distribution functions are the bi-Maxwellian and the
ring distributions. In this thesis, we have examined the electrostatic instability of
a ring distribution function. It was found analytically that the ring distribution
is electrostatically stable. Moreover, numerical simulations using the particle-incell
approach show that certain incomplete (anisotropic) ring distributions can
collapse to a complete (isotropic) ring distribution, through an electrostatic instability.
In additional particle-in-cell simulations, we confirm the prediction of
a previous analytical model of the effects of collisions on the Weibel instability
of a bi-Maxwellian electron distribution. Using the previously known analytical
model, it is found that collisions could play a major role in the Weibel instability
in laboratory plasmas. We find that the evolution of the non-fluctuating part of
the distribution is important during the time the instability grows to significant
amplitudes. Thus, the strength of the seed fluctuations in the beginning of the
simulation or experiment can impact the observed growth.
Beskrivning
Ämne/nyckelord
plasma , 2D-isotropic electrostatic stability , two-stream instability , Weibel instability , collisions , particle-in-cell simulation