The influence of spatially and temporally varying edge conditions on the interpretation of spectroscopic particle flux measurements

Photon fluxes emerging from the plasma boundary in the vicinity of material surfaces are often directly interpreted in terms of particle fluxes. The factor of proportionality (inverse photon efficiency) is the ratio of the ionization and excitation probabilities, S/XB, including the branching ratio B. Generally, S/XB is taken to be constant and represented by an average value which is typical for the plasma parameters where ionization and excitation is essential. This approach is convenient and justified, as long as S/XB is nearly independent of the density and a weak function of temperature. If these conditions do not apply, however, or very fast changes in the plasma conditions occur, a more sophisticated analysis is necessary. We have developed a simple numerical model to interpret the measured photon fluxes under such general conditions. The penetration, ionization and transport of impurity atoms is modelled using measured density and temperature profiles and estimated values for the energy of the sputtered particles. The photon efficiencies obtained exhibit considerable variations with the plasma density and diffusion coefficient. (author) 5 refs., 5 figs