Electron-ion collisional rate coefficients from time-dependent plasmas

Abstract

Measurements of effective collisional electron-ion rate coefficients for ionization, dielectronic recombination and excitation, performed using methods of quantitative spectroscopy, are reviewed. These methods are based on the corona model for excitation and ionization, modified to account for two-step processes, etc., if necessary. Plasma parameters are determined using independent methods, mostly Thomson scattering of laser radiation for the electron temperature and density. A large number of ionization rate coefficients have been obtained with an expected accuracy approaching 30%. For dielectronic recombination, the number of measurements is much smaller and the expected accuracy is typically about a factor of 2. For both processes, the highest ionic charge for which measurements based on time-dependent radiation have been reported is ~30. For excitation, the number of rate coefficients obtained is intermediate to those for ionization and dielectronic recombination. The expected accuracy is often limited by errors in the intensity calibration and in the determination of impurity densities. The highest charge is 16 for such measurements of excitation rates.