Influence of broadband photocoupling onK-shell excitation in aluminum

A detailed theoretical model of the collisional and radiative couplings within the aluminum $K$ shell is described which has been used to self-consistently calculate the functional dependence of the excitation state of the $K$ shell and its emission spectrum on ambient plasma conditions for a wide range of $K$-shell opacities. Both line and continuum couplings are included in the model over a range of photon energies from 442 eV to 6.13 keV. The approach of the interior of the aluminum plasma to local thermodynamic equilibrium has been investigated for millimeter sized plasmas where the $K$-shell couplings are photodominated and the plasma interior must come into radiative equilibrium. The approach of the $K$-series emission spectrum, which includes satellite and intercombination lines of the heliumlike resonance line, to the blackbody curve is computed. Temperature variations of the power output in continuum and line radiation are also computed and discussed. Finally, a set of calculations that relate to the ability of an external source of x radiation to selectively photopump the $3p$ state and maintain an inversion between $2p-3d$ levels within the heliumlike ionization stage is described. Two important effects are seen. One, the opacity of the heliumlike $L\alpha$ line plays an important role in determining the ability of the external radiation to invert levels within the plasma interior, and two, the inversion saturates with increasing pump strengths as the heliumlike ground-state population is depleted by the pump.