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This thesis investigates how magnetographic data may be used to study the longterm behaviour of the magnetic field distribution across the surface of the sun.

In this thesis the following problems are studied: 1-Relativistic self-focusing and channelling of intense laser pulses have been studied in underdense plasma using 2D PIC simulations, for different laser powers and plasma densities. Analytical solutions for the stationary evacuated channels have been recovered in PIC simulations. It is shown that otherwise stable channels can accelerate electrons due to surface waves on the walls of the channels. Relativistic filaments with finite electron density are unstable to transverse modulations which lead in the nonlinear stage to the break-up of laser pulses into independent filaments. 2-Although 3D simulations are limited, they are more realistic. Azimuthal stability of the laser pulses in interaction with underdense plasma can only be studied in 3D geometry. Relativistic self-focusing and channelling of intense laser pulses have been studied in underdense plasma using 3D PIC simulations, for different laser powers and plasma densities. Analytical solutions for the stationary evacuated channels and ring structure have been recovered in PIC simulations. The stability of ring structure due to azimuthal perturbations has been studied both in theory and in simulations. The gain length of such instability is smaller at higher densities $(>0.1n_{cr})$. It is shown that the azimuthal perturbation can break up the azimuthal symmetry of the laser pulse. 3-Working with circularly polarized laser pulses, gave us a motivation to study Inverse Faraday Effect in interaction of circularly polarized laser pulses with plasma. Axial magnetic field generation by intense circularly polarized laser beams in underdense plasmas has been studied with 3D particle-in-cell (PIC) simulations and by means of theoretical analysis. The source of azimuthal nonlinear currents and of the axial magnetic field depends on the transverse inhomogeneities of the electron density and laser intensity. The fields reach maximum strength of several tens of MG for laser pulses undergoing relativistic self-focusing and channelling in moderately relativistic regime. 4-Electron wakefield acceleration was studied in support of the experiment which was carried on using 7 TW laser beam at Canadian Advanced Laser Light source facility. 2D simulations were performed to study this problem. The energy the electrons gained in the process was peaked at 20-30 Mev close to the experimental results.

It has been found that a small magnetic field (<300 mT) can substantial change the electroluminescence, photoluminescence, photocurrent, electrical injection current in nonmagnetic organic semiconductors. It is generally believed that these magnetic field effects (MFE) are related to the spin dependent processes in organic semiconductor. However, the origin of MFE is still not well understood. In this dissertation, we investigate the underlying mechanism for magnetic field effects on electroluminescence (MFEEL) and magnetoresistance (MR) and demonstrate the complete tuning of MFEEL and MR based on our theoretical understanding. We consider MFE arising from magnetic field sensitive intersystem crossing (ISC) and triplet charge reaction. Magnetic field can increase the singlet ratios through ISC, accounting for positive MFEEL. Magnetic field modulated ISC strongly depends on the electron-hole pair separation distance. MFE can be enhanced by increasing the electron hole pair distance through material mixing and interplaying the electric dipole-dipole interaction. Meanwhile, two possible mechanisms corresponding for negative MFEEL: triplet-triplet annihilation and triplet charge reaction are also discussed. The negative MFEEL is achieved through adjusting triplet density charge confinement and exciton/charge ratio, which indicates that triplet charge reaction is a dominate process accountable for negative MFEEL. Significant MR and MFEEL are observed in strong spin orbital coupling iridium complex based OLED device after introducing the non-magnetic insulating blocking PVA layer. A possible mechanism for this new interface induced MR and MFEEL is proposed based on magnetic field perturbed spin-spin interaction at short capture distance of inter-charge carriers. The comparative study of two strong spin orbital coupling materials Ir(ppy)3 and Ir(ppy)2(acac) with different electrical dipole moments indicate the electric dipole-dipole interaction can change MR and MFEEL from short distance capture based regime to long distance intersystem-crossing regime. At last, we demonstrate the fully tuning sign of magnetic field effect on the fluorescence (MFEFEL) and phosphorescence (MFEPEL) by using the ISC, energy transfer and spin-spin interaction. In addition, we demonstrate a giant MFEEL (400%) in electrochemical cells and attribute this giant MFEEL to Lorentz force driven ion transport and Lorentz force dependent diffusion layer thickness through convection.

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This study uses the PIC (particle-in-cell) method to simulate unsteady three-dimensional behavior in argon plasma under low pressure , low density between two plates. Plasma has been widely used in materials processing, film manufacturing, nuclear fusion , light source , etc. It is therefore important to study Plasma behavior . This model ignores secondary electron emission , recombination between ions and electrons and assumes a uniform distribution of the neutrals having velocity of a Maxwellian distribution. The lower plate in subject to a biased voltage and magnetic field. The result show the effects of a biased voltage in density and velocity of the ion and electron with the low plate.

This thesis presents a computational analysis of the magnetic field of low-frequency power transmission lines, and the approaches to its suppression. First, according to the structure of Taiwan's three-phase A.C. transmission network, this research calculated the distribution of conducting wires' magnetic field under specific configuration by applying the theories of Near-field effect, Biot Savart's law, and double complex number. Second, this research explored the features of various approaches to magnetic field suppression with magnetic-field vector analyses and Matlab simulations. Finally, two magnetic-field cancellation methods, the ¡§circuit space arrangement¡¨ and ¡§time phase permutations¡¨ were adopted to investigate their magnetic effects under various structures and combinations of transmission lines. This study reveals that the magnetic field can be effectively suppressed by using appropriate configuration of transmission lines in space and phase. By applying the result to the design and construction of transmission lines, we can meet not only the requirements of magnetic field reduction, but also the needs of the least cost.