Applications of NLTE population kinetics

The emission from atoms and ions, i.e., the plasma spectroscopy, provides one of the most unambiguous and powerful methods for the understanding of basic phenomena in laboratory and astrophysical plasmas. We present in a set of examples of the application of NLTE population kinetic data, which is fundamental for predicting plasma spectroscopic observables. We provide examples of previous experimental analyses or experimental designs where problems were identified, but where the solutions to those problems have not yet been identified. In these cases it is found that interest wanes more quickly than the time required to resolve the problems. Further, we use cases in which the applications are purely of diagnostic interest; i.e., we show examples where the results of population kinetics codes can be used to generate qualitative or quantitative answers that can be compared with data. In this review the interest is to discuss the complexity of the models required, the methods employed to estimate the accuracy of the resultant diagnostic, and the range of applicability of the method. Finally, we also touch on applications where the state-of-the-art in NLTE population kinetics modeling is currently unable to address the problems and where developments are needed.