Contribution of excited hydrogen atoms to charge-exchange excitation of impurities in fusion plasmas

Cross sections are calculated for charge transfer into excited states of C⁵⁺ and O⁷⁺ from collisions of C⁶⁺ and O⁸⁺ with hydrogen atoms in the n=2 and 3 levels. Effective emission cross sections that account for cascading are then derived for spectral lines emitted when the product ions decay. These are compared to the emission cross sections calculated for excitation by ground-state hydrogen. It is shown that in some circumstances the contribution from excited hydrogen atoms must be taken into account when visible lines are used to determine the oxygen or carbon density from charge-exchange spectroscopy in plasmas. Influences on Lyman-series spectra in the x-ray region are also discussed.