Theoretical Study On Atom Collision Processes In Ultracold Plasma

Atomic process have attracted much intrest for many years in view of their important role in both fundamental and applicate physics like confinement fusion, weapon physics and astrophysics. For the limitation of the expermtal techniques, the experiment is always on the collision between atoms on ground state and ions or electrons. Recently, C.C Lin used the ultracold atom method to make a excited state target for studying collision between electrons and excited atoms. On the other side, T. C. Killian made the first ultracold plasma experiment utilized the lasercooling method. Our experiment group is trying to use the ultracold plasma technique to study atom processes in the plasma. In this article, we theoretically study the atomic processes in our experiment.For studying the collsion between ions and excited atoms, the charge exchange process in collisions of H+ with Li(5d) is investigated using the two-center atomic-orbital close-coupling method. The state-selective cross sections are obtained in the energy range of 0.5-10keV. It's found that the processes for capture to n=4-7 are the dominant reactions, and the n-distribution of state-selective cross sections is weakly dependent on the collision energy. But the l-distribution of state-selective cross sections strongly relies on the collision energy.The electron capture in O⁶⁺-H collisions is studied by the two-center atomic orbital close-coupling (TC-AOCC) method when the interactions of charged particles are screened and have a Yukawa form. Atomic orbitals and eigenenergies of n≤6 states on O(5+) and n≤2 states on H are calculated as a function of the interaction screening parameter and used in the AOCC dynamics scheme to calculate the electron capture cross sections in the energy range 1-200keV/u.Charge transfer processes in collisions of O⁶⁺ and C⁴+ with ground state He and H2 are investigated using the two-center atomic orbital close-coupling method. Total and state-selective one-electron capture cross sections are obtained for collision energies between 0.5 and 500keV/u. The polarization degrees of 3p²P_3/2-3s²S_1/2 radiation from O⁵⁺(3p²P_3/2) and C³⁺(3p²P_3/2) produced in O⁶+, C⁴+ collision with He and H2 are calculated from the magnetic substate-selective cross sections with inclusion of cascade contributions from higher n=4 and n=5 states. Good agreement is obtained with the experimental data available in the energy range 3– 8keV/u.The expansion of the ultracold plasma is investigated by the rate equation method with atomic process parameters. The Rydberg atoms are found in 1μs after the ultracold plasma is produced.In the end of this dissertation, some useful expansion of the TC-AOCC method is given.