Ultracold plasmas and guiding center drift atoms

This thesis discusses theory questions suggested by recent experiments with ultracold plasmas. In one class of experiments, ultracold plasmas are produced by abruptly photoionizing small clouds of laser cooled atoms, adjusting the photon energy to barely exceed the ionization energy of the cooled atoms. The thesis presents molecular dynamics simulation for the early time evolution of such plasmas. Contrary to earlier speculation, no evidence of strong electron-electron correlations is observed in the simulations even if the initial value of the coupling parameter (Gammae = e2/akTe) is much larger than unity. As electron-electron correlations begin to develop, the correlation energy is released to heat the electrons, raising the electron temperature to the point where Gammae ∼ 1 and limiting further development of correlation. Further heating of the electrons occurs as a by-product of three-body recombination. When a model of laser cooling is added to the simulation, the formation of strong ion-ion correlation is observed. Contrary to earlier suggestion, the rate of three-body recombination is observed to be in reasonable agreement with the traditional formula, R = 3.9 x 10-9 sec-1[ n (cm-3)]2 [Te(° K)]-9/2, but care must be taken to use the correct temporally evolving temperature, Te.; Also, the thesis describes the novel dynamics of "guiding center drift atoms". The weakly bound and strongly magnetized antihydrogen atoms recently produced in ultracold plasmas at CERN are examples of such atoms. The atoms are quasi-classical, and the dynamics of the positron is well described by guiding center drift theory. Because of a frequency ordering, the dynamics is integrable, and the thesis characterizes the possible motions of the weakly bound positron-antiproton pair as a function of constants of the motion. Quantum numbers are assigned using the Bohr-Sommerfeld prescription. The thesis also discusses the center of mass motion of the atoms in an electric and magnetic field. The effective electric field in the moving frame of the atom polarizes the atom, and the gradients in the field give rise to a force on the atom. An approximate equation of motion for the atom center of mass is obtained by averaging over the rapid internal dynamics of the atom. Experimentally relevant applications of the equation of motion are discussed. Finally, the critical field for ionization is determined as an upper bound on the range of applicability of the theory.