Self-absorption models and electron temperature determination in hid lamps

Summary form only given. The validity of the one-parameter approximation (OPA) for the source function to deduce the emissivity at the maximum of a self-reversed spectral line is proved by comparison with exact solutions of the radiation transfer equation and applied to the temperature determination of Hg-NaI and Hg-TlI arc lamps from the measurement of the intensity at the line peak. In the OPA the source function is described by a power law the exponent of which is the inhomogeneity parameter. Using radial density profiles for the emitting and absorbing particles it was proved that for a given inhomogeneity parameter the exact and approximated temperature differs by only less than 0.5% independently of the plasma-equilibrium state and the transition probabilities. On the other hand, comparison of the approximated solution with the exact solution using now trial normalized source functions proves that the accuracy of the OPA in reproducing the line contour is significantly higher than that of the Bartels. The theoretical results indicate that the inhomogeneity parameter can be deduced from the characteristics of the emitted lines with sufficient accuracy when the optical depth at the line center is less than about 7. Independent experimental measurements have surprisingly shown that in fact the optical depth within the studied lines is lower than 6. This effect is in accordance with the predictions of the resonance radiation transfer in a dispersive medium. Experimental results of the electron temperature as well as the excitation temperature of the resonance metal-atoms states are presented