Low-frequency Waves In Magnetic Reconnection And Solitary Kinetic Alfven Waves In Adiabatic Process

This thesis is focused on the the low-frequency waves in magnetic reconnection and solitary kinetic Alfven waves in an adiabatic process.1.Low-frequency waves in magnetic reconnection:Magnetic reconnection plays an important role in space plasma physics. It can ef-ficiently transfer and transform the material, momentum, and energy of plasmas.There are lots of eruptive activities in space plasmas and interactions between the solar wind and Earth’s magnetosphere that relate to magnetic reconnection. Plasma waves are im-portant to magnetic reconnection. Because there is a possibility that magnetic recon-nection is triggered by some plasma waves, also lots of plasma waves can be excited during the magnetic reconnection process. This thesis focuses on the characteristics of the low-frequency waves that are produced by magnetic reconnection.A two-dimensional hybrid simulation code is carried out to simulate the magnetic reconnection process. In the coordinate moving with fluid, wave spectrums are obtained by the fast Fourier transformation of magnetic field component which are perpendicular to the magnetic reconnection plane, and wave propagation directions and polarizations are determined by the minimum variance analysis of the electric field.After the recon-nection becoming quasi-steady, the space distributions of waves are studied.The results show that low-frequency Alfven ion-cyclotron waves are dominating in reconnection area. The frequencies of these waves are between0and1local proton gyrofrequency, the polarizations are all left-handed. In the inflow regions the dominant waves are Alfven ion-cyclotron waves with smaller amplitudes and propagation direc-tions mainly along the ambient magnetic field, these waves have higher frequencies, the main peaks of spectrums are usually higher than half of the local proton gyrofrequency. The large amplitude turbulence with frequency of0-0.6local proton gyrofrequency and isotropic propagation direction dominates in the outflow regions. We believe that the magnetic reconnection can produce Alfven waves, and some observational evidences are presented. A comparison of our results with another paper which investigates wave propagation with hybrid code is carried out to prove the correction of our results and explain the observations.The large-scale turbulence in the outflow regions can affect the Hall quadrupole structure distribution and produce some inverted distribution which agrees with some of the observations.2. Solitary kinetic Alfven waves in an adiabatic process:Solitary Kinetic Alfven Waves (SKAWs) are important in the field of space plas-ma physics because of their nonzero parallel electrical fields and density fluctuations. SKAWs play significant roles in wave-particle interaction and magnetosphere-ionosphere coupling. They have been investigated extensively through observation and theoretic-s with a focus on charged particle acceleration and heating. However, those studies were done under the simplifying assumption that the whole process was an isothermal process.In reality, the adiabatic index varies significantly under different plasma con-ditions. Therefor it is necessary to investigate the influence of changing adiabatic index on the SKAWs.Under different thermodynamic processes, SKAWs with the limit of small ampli-tudes are studied analytically and numerically by the method of the Sagdeev potential. The results show that as the adiabatic index increases, the amplitude of the solitary struc-ture and perturbed electric field along the background magnetic field direction reduce, the width of the solitary structure and perturbed electromagnetic fields which are per-pendicular to the background magnetic field direction increase. The results also show that the modifications of an adiabatic process to the isothermal process is significan-t. Therefor it is necessary to consider the modifications in plasmas where the electron thermal effect is much stronger than electron inertial effect, such as in the solar wind and in the pole regions of the Earth’s magnetosphere.