Diagnostics of thermal plasma

Abstract

The state of complete thermodynamic equilibrium (TE) can only be established in a plasma, when it is enclosed in a cavity with walls kept at a fixed temperature. Once the cavity is removed, the plasma will lose energy by heat currents, diffusion processes and radiation. In order to compensate for these losses, the plasma has to be heated continuously. This will cause gradients of all plasma parameters. It is obvious, that such a system is no longer in complete TE. It is therefore the first step in plasma diagnostics, to get information about the actual state of the respective plasma. In the following a number of different experimental techniques as e.g. emission spectroscopy, interferometry and laser light scattering are discussed. The desired plasma parameters can be obtained from the results of the various measurements, when the appropriate plasma model is known. © 1988 IUPAC