Measurement of electron impact excitation cross sections for heliumlike titanium

We have obtained the first measurement of electron impact excitation cross sections as a function of energy for a highly charged ion. Collisional excitation cross sections to four n=2 levels of He-like titanium were measured from threshold to 1.7 times threshold. The data conform well to established theory, especially for direct excitation; however, significant differences are found with predicted contributions from resonance excitation and in the treatment of radiative cascades. The latter changes plasma temperatures inferred from titanium Kα line intensities by as much as a factor of 2