Dust grain evolution and interaction in gas-plasma mixtures

Alharbi, Mariam Break (2015) Dust grain evolution and interaction in gas-plasma mixtures. PhD thesis, University of Glasgow.

Abstract

The main aim of this thesis is to understand and investigate some essential phys- ical processes leading to dust grain growth and their interactions in plasmas. This is achieved by applying both analytic and numerical models. Three main situations are explored: dust grains growth in presence of electrostatic and electromagnetic fields, dust grains interaction in submicron scales, and collective effects of dust grains above thundercloud.
The evolution and character of plasma dust has wide-ranging implications for astro- physics and laboratory plasmas, including plasma processes and fusion devices. The local electromagnetic fields can influence the conditions for dust growth, leading in some cases to naturally occurring prolate-spheroidal dust shapes. However, presence of magnetic fields can have significant effects on dust growth. Results for dust growth by ion accretion under the combined influence of an applied magnetic field and the evolving electrostatic field arising from the charged grain in 1D and 3D have been presented. The calculations show that most ions starting near the grain surface ulti- mately collide with it, while those starting further away execute orbital motion around the magnetic field lines and drift toward the grain. Moreover, the energy spectrum for impacting ions shows discrete structure in presence of a parallel oriented magnetic field. Finally, we note that the magnetic field influences the spatial deposition pattern of ions, leading to increasing ions fluxes at the grain ends.
Microdischarge plasmas is an electrical discharges which occurs in geometries in range of sub-millimetre length scales. However, a much extreme situation than mi- crodischarge plasma where small size charged dust grains can cause breakdown for the neutral gas when dust inter space reach to sub-micro scales. The interactions of charged dust grains in plasma where molecules of Oxygen gas are present and the ef- fect on the discharge of the ambient gas is investigated in presence of magnetic field.The particle in cell model was used to simulate electrons motion in addition to using Monte Carlo method to simulate the electrons collisions with neutrals. The importance of the magnetic field was explored by varying the parameter (p) which gives the rela- tive size of the electric field to the magnetic field. The distribution of electrons kinetic energies was investigated in two cases when (p = 103) and (p = 102). At the first case the gained energy increased dramatically, however, the gained energy did not ex- ceed further than the metastables threshold as a result of consuming electrons energy in metastable collisions. When magnetic field is increased (p = 102), gained energy is fluctuated as a results of contribution in gyromotion orbits and electrons only involved in metastable collisions. However, a number of metastable in this case is lower than (p = 103) case.
The electron beam can occur just after sprites. The presence of charged dust above thundercloud are thought to have a basic role in the electron beam formation in which the electrons avalanche in sprite event leaving an environment of negative charged dust and positive ions. This environment was simulated in a model like hollow cathode with a column of positive ions inside. The particle in cell method was used to simulate particles motion. Results for electrons evolution in such this environment with and without presence of positive ions were presented. Electrons in environment without positive ions evolve upwards gaining lower final energy. For the case when positive column is presented, electrons evolve upwards in a long path and do not biased to sidewalls. The trajectory of the electron shows an oscillator motion. The period of such motion depends on the electron’s original position. Electrons gain higher energy in a shorter time comparing to the case when the ions column is not simulated.

• Item Type: Thesis (PhD)
• Qualification Level: Masters
• Keywords: Dust grain interaction, plasma-gas mixture
• Subjects: Q Science > QB Astronomy; Q Science > QC Physics
• Colleges/Schools: College of Science and Engineering > School of Physics and Astronomy
• Supervisor's Name: Diver, Dr. Declan
• Date of Award: 2015
• Depositing User: Mrs Mariam Alharbi
• Unique ID: glathesis:2015-6355
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 22 May 2015 15:41
• Last Modified: 22 May 2015 15:46
• URI: https://theses.gla.ac.uk/id/eprint/6355