In addition to the most general applications of spectroscopic methods to density and temperature measurements, which were discussed in the two preceding chapters, there are numerous special applications. Some of these will be discussed in this concluding chapter, without any prejudice against any well-established or recently developed methods which are omitted. If there is any common thread, it is in the strong role played by atomic collision theory and by the physics of atoms and ions in electric and magnetic fields. As in the other chapters, no attempt will be made to describe the often very sophisticated instrumentation or other experimental details, which the interested reader should be able to find with the help of the references in the original papers.

The first two special applications to be discussed, namely charge exchange recombination and beam emission spectroscopy, obviate the essential difficulty in emission or absorption spectroscopy in obtaining spatial resolution along the line of sight. This is accomplished by injecting heating or diagnostic neutral beams into magnetically confined plasmas either to preferentially populate some excited states of plasma ions by charge exchange recombination, as discussed in section 6.5, or by having the atoms in the beam ionized and excited by the plasma electrons, as discussed in sections 6.2 and 6.3, or even by protons and other plasma ions (Mandl et al. 1993), see section 6.5.