Observation of excited level populations of Li-like aluminium ions in a recombining plasma: role of atomic processes involving doubly excited levels of Be-like ions

Abstract

An aluminium slab target was irradiated by multiple pulses of Nd:glass laser light with the irradiance of . After the laser irradiation, a laser-produced aluminium plasma was observed in its recombining phase using a spectrometer whose relative sensitivity was calibrated. We measured relative intensities of the resonance series lines and the lines of the - and - series of the Li-like aluminium ions and derived the excited level populations of the upper levels. From the slope of the population distribution of the high-lying excited levels and the transition from the series lines to the continuum, the electron temperature and the electron density were estimated to be 8 eV and 3-. A comparison of the experimental population distribution with a collisional-radiative (CR) model calculation indicates that recombination of the excited Li-like ions through doubly excited levels of the Be-like ions plays an important role in the population kinetics of the Li-like ions.