Radiative Processes in Plasmas

Abstract

All plasmas emit and absorb electromagnetic radiation and Fig. 6.1 shows, as an example, the characteristics of the emission spectrum of a dense laboratory hydrogen plasma with some impurities at the electron temperature ofk_BT_e = 10 eV. The dashed line is the blackbody limit drawn for comparison. We identify the following contributions: – Bremsstrahlung (dot–dashed contribution), a continuum radiation, is emitted when the electrons experience deflection in the electric field of the ions. At long wavelengths the optical depth becomes large and the bremsstrahlung approaches the blackbody limit (Planck function). – Recombination radiation, also a continuum but characterized by edges. It is emitted when electrons recombine with ions. – Line radiation corresponds to transitions of electrons between levels inatoms and ions, and at low temperatures also in molecules. Lines may become optically thick especially at long wavelengths and then they also reach the blackbody limit.