STATE-SELECTIVE ELECTRON-CAPTURE IN COLLISIONS OF SLOW FE3+ AND FE4+ IONS WITH H AND HE ATOMS

Translational energy spectroscopy in an apparatus previously developed in this laboratory has been used to study state-selective one-electron capture by Fe-q+ (q = 3, 4) ions in collisions with He and H at energies of q x 2 and q x 4 keV. The data, which are the first of their type, are relevant to a better understanding of the plasma edge and neutral beam heating and diagnostics in fusion energy devices. The main excited products are shown to arise through electron capture into n = 3 and n = 4 states. Electron capture by Fe3+ ions is shown to be dominated by many collision channels involving metastable ions which preclude a detailed analysis. In contrast, observed energy change spectra for Fe4+ impact can be satisfactorily interpreted in terms of a predominant contribution from collision channels involving ground state primary ions. MCLZ calculations have also been carried out and compared with experiment for both Fe4+-He and Fe4+-H collisions.