Modeling Non-LTE Oxygen-like Multiplet Dynamics in Intense Laser-produced Xenon Plasmas

An often used approximation employed to simplify the problem of modeling the L- and M-shell ionization dynamics of moderate to high atomic number plasmas is to lump the states within each $n\ell$ multiplet of each ionization stage by assuming the multiplet substates are in LTE with respect to one another. In plasmas created by intense laser pulses ($10^20$ W/cm$^{-2}$) irradiating a gas of xenon clusters, this assumption breaks down. A diagnostic for this breakdown is the appearance of a strongly amplified x-ray line at 2.9 \AA. In this talk, we study the subpopulation dynamics in the O-like ionization stage of Xe where significant amounts of population can be stored in excited states. The non-LTE behavior of the following states is calculated: the ground states, the $\Delta n=0$, and the $2p^33\ell$ or $2p^23\ell$ excited states of O-like Xe, and used to determine the impact on lumped state excitation and ionization rates and on the possibility of generating a population inversion between the substates of the n=2 and n=3 states. In particular, the reduction of the lumped state Einstein decay rates of the $n=3$ states as a function of ion density is calculated.\footnote{K. G. Whitney, et. al., J. Phys. B, \bf{40}, 2747 (2007).}