9 - Radiation losses

Summary

In this and the following chapters, various applications of plasma spectroscopy will be discussed. Their selection is necessarily somewhat arbitrary, but they will hopefully serve as useful demonstrations of the general methods and principles described in the preceding chapters. A very broad class of applications is concerned with the energy loss or gain of plasmas because of emission or absorption of electromagnetic radiation. As usual, the need for comprehensive calculations of these processes is shared with astrophysics. Here the requirement of energy conservation within a stellar atmosphere not subject to any significant nonradiative energy transport must be imposed by having zero divergence of the spectrally integrated radiative flux which, in turn, is obtained from the radiative energy transfer equations of the preceding chapter. In many laboratory plasmas such a general approach is not necessary, because most of the emission normally comes from optically thin layers and because radiative heating, except for radio-frequency (Golant and Fedorov 1989) and microwave heating (Bekefi 1966), is not involved.

Very notable exceptions to the last point are laser-produced plasmas, in which the absorption of the, typically, visible laser light is indeed essential (Kruer 1988). Other exceptions are x-ray heated plasmas produced, e.g., for the measurement of absorption coefficients of hot and dense low, medium and high Z materials (Davidson et al. 1988, Foster et al. 1991, Perry et al. 1991, Springer et al. 1992, 1994, Schwanda and Eidmann 1992, DaSilva et al. 1992, Eidmann et al. 1994, Winhart et al. 1995).