Ionization rate coefficients of multiply ionized atoms

Ionization rate coefficients of He-like boron and carbon have been deduced from the time histories of the spectral lines emitted by BIV and CV ions in a small $\theta$-pinch plasma. The radial electron density (∼5× ${10}^{15}$ ${\mathrm{cm}}^{-3\mathrm{}}$) and temperature (∼220 eV) profiles were determined by 90° Thomson scattering. After making appropriate corrections for two-step ionization via the metastable $\mathrm{}\left(1s2s\right)\mathrm{}{}_{}{}^3{}_{}{}^{}S_1^{}{}_{}{}^{}$ level, theoretical estimates were found to agree with experimental results. A comparison of the above and previously measured ionization rates for various ions with existing theoretical predictions shows that the semiclassical theory of Burgess yields values that are in good agreement with experiment, especially at higher temperatures. For removal of $1s$ electrons, semiempirical rate coefficients are also in agreement with experiment, but are too large by a factor ∼2 for other electrons.