Plasma Spectroscopy

The population of excited levels (and the ground state) of atoms and ions has been the subject of conventional intensity spectroscopy, because the upper level population of the emission line gives its observed intensity. In this chapter, we review the collisional-radiative (CR) model which is a versatile tool in dealing with the problem of the population. In this framework, we define the ionizing plasma and the recombining plasma. Many laboratory plasmas fall into either class in this category. We examine various features of plasmas in each class. We introduce the concept of the ionization balance and examine the population characteristics of the ionization-balance plasma. This chapter forms the basis of the population-alignment collisional-radiative model (PACR model), by which we are able to deal with the Class 2 polarization phenomena, to be discussed in the succeeding chapter.