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| INSTITUTET FÖR RYMDFYSIK | UPPSALA |
 |
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| Swedish Institute of Space Physics | (59°50.272′N, 17°38.786′E) |
Student Project (15 c)/Studentprojekt (15 hp)
Kinetic simulation of spherically symmetric collisionless plasma in the inner part of a cometary coma
Student: Pavel Dogurevich, Uppsala UniversitySupervisor: Anders Eriksson
Period: Spring 2019
Background
Comet nuclei emit gas (mostly water vapour). As the comet gravity is weak this gas expands freely into space around it. Solar EUV radiation as well as energetic particles ionizes some of the gas molecules, providing the comet with an expanding ionosphere. This interacts with the solar wind and interplanetary magnetic field (IMF) giving a very complex and dynamic environment. However, for sufficiently active comets the IMF cannot penetrate the region closest to the nucleus. For this region an assumption of spherical symmetry is not unreasonable. This has been used in several previous fluid models of the inner coma, but such models can only represent the energy distribution of the electrons by a Boltzmann distribution. In reality, electric fields may trap part of the electrons, and to model such phenomena a kinetic approach is needed.Project
The goal of this project was to set up a spherically symmetric model of the inner coma, including continuous ionization but no collisional processes or recombination, implement it on an ordinary personal computer and evaluate the results. The simulations do not aim at a realistic model but can be seen as a first step toward understanding parts of the electron kinetics in the coma. The project was succesful in that such simulations could be performed, with the newborn electrons distributed isotropically in direction but monoenergetically in space, though only for a very short simulation time and for ionization only in a finite shell. Nevertheless, an ambipolar potential well formed around the nucleus, and bound electron orbits could be observed.Results
Project report
![[G-S reconstruction]](eorb.png)
Example of the phase space trajectory of an electron trapped in the ambipolar potential well forming around the cometary nucleus.