MEASUREMENT OF LEVEL-SPECIFIC DIELECTRONIC-RECOMBINATION CROSS-SECTIONS OF HELIUM-LIKE FE-XXV

The strengths of individual 1s2l2l' resonances for dielectronic recombination of heliumlike iron are measured on an electron-beam ion trap using high-resolution x-ray spectroscopy. An energy resolution DELTAE/E of better than 0.1% is achieved by monitoring the exit channel of the recombination process. Dielectronic-resonance strengths are measured relative to the cross section for nonresonant radiative electron capture of heliumlike Fe XXV, and an overall uncertainty of 20% is achieved. Good agreement with theory is found for the strongest resonances; however, less good agreement is found for the weaker resonances. The results indicate that further theoretical and experimental efforts are necessary to reliably use weak dielectronic satellite lines in plasma diagnostics.