Theoretical Research On Temperature Relaxation In Plasmas

In a non-equilibrium plasma, temperature relaxation (TR) arises when the parallel temperature of one species of particles is different from its perpendicular temperature or the temperatures of different species are not the same. Due to the large mass ratio of the electron to the ion, the energy exchange between electrons and ions is small when their temperatures are of the same order and considered not to play an important role in anisotropic electron and ion TR. However, in the presence of a magnetic field, when the electron thermal gyro-radius is smaller than the screening length, the energy exchange rates between different components of the electrons and ions are different. This differ-ence will affect weakly-anisotropic TR. It has been pointed out by many authors that the electron-ion TR rate contains a doubly logarithmic term in the presence of a strong magnetic field, but no one shows the energy exchange between which two components lead to this term. This problem can be solved only based on quasi-Maxwellian distri-bution which involves two temperatures, i.e., parallel and perpendicular (with respect to the magnetic field) temperatures Tα||, Tα⊥(α denoting species). Bearing above two points in mind, in this dissertation we investigate the TR in a two-component plasma composed of electrons and one type of positive ions on the basis of binary collision model. The main content are as follows.1. The binary collisions between two gyrating charged particles are considered in a perturbative manner. By using expansion and iterative method, the first-and second-order velocity changes of the particles during the collision are calculated and the average time rates of change of the particles’parallel and perpendicular energies are obtained. Expressions for the time rates of change of the parallel and perpendicular temperatures are then derived, from which we can see that the effects of magnetic field on the energy exchange rates between different compo-nents of the two groups of particles are not the same. Moreover, the validity of the perturbation theory is justified and different cutoff ways are given in order to obtain accurate results whether a magnetic field is present or not.2. Anisotropic TR is investigated. By use of the expressions for the time rates of change of the parallel and perpendicular temperatures, anisotropic TR is re-searched whether a magnetic field is present or not. In the case of no magnetic field, assuming that the distributions of electrons and ions are both anisotropic, we find that in some cases the anisotropy of electron distribution will affect anisotropic ion TR and vice versa. When a homogeneous and static magnetic field is present, for small anisotropies and Z(?)<<(?)<<(?), where ma and Ta are the mass and temperature of a-species particles, respec-tively, α=e,i, Z is the charge number of ions, exchange rates between dif-ferent components of the electron and ion kinetic energies are calculated and anisotropic electron and ion TR rates veiB(2) and vieB (2) arising from the energy exchange between electrons and ions are obtained. Two terms proportional to (Ti-Te)/(Te||-Te⊥) and (Ti-Te)/(Ti||-Ti⊥) appears respectively in veiB(2) and vieB (2), whose coefficients become much larger than the other terms’in the strong magnetic field, and result in large values of veiB(2) and vieB (2). This implies that the energy exchange between electrons and ions affect anisotropic electron and ion TR significantly.3. The effects of magnetic field on isotropic TR are studied. Based on the quasi-Maxwell distribution, the like-particle TR rate and electron-ion TR rate are ob-tained. It is shown that although the magnetic field affects the energy exchange between different components of the two pieces of like particle largely, its influ-ence on the like-particle TR is not significant; the exchange between the elec-tron parallel and ion perpendicular kinetic energies speeds up significantly in the strong magnetic field and this results in a large electron-ion TR rate close to two times of the value of no magnetic field case.