5 Conclusions

Two CR models of highly ionized calcium have been benchmarked in this work by comparing their predictions to the line intensities, measured with an absolutely calibrated grazing incidence spectrometer in two tokamak experiments. The CR models are based on ab initio HULLAC and CHIANTI atomic data, which are the state of the art in atomic structure calculations. The HULLAC models are in a good agreement with most measured lines of lithium-like to fluorine-like calcium. CHIANTI predictions for several Ca XVI and Ca XIV lines are inconsistent with our measurements and HULLAC calculations. It is shown that for the tokamak, as well as for the solar flare plasma conditions, collisional-radiative models which include n =2 and n = 3 configurations are adequate to predict L-shell line intensities. At these plasma conditions, radiative or collisional cascades from n =4 , 5 levels are generally insignificant, and quasi-steady state approach applies well. With the present state of atomic calculations, likely explanations for large discrepancies with experimental data are transient or kinetic effects, not the atomic data quality. Total ionization and recombination rates which are used by Mazzotta et al. ([1998]) for a new calcium fractional abundances calculation, have been used for a calcium L-shell spectrum simulation. A synthetic line-integrated spectrum which includes over two hundred lines in the range 50 - 360 Å, predicted by HULLAC, closely reproduces the spectrum recorded at the TEXT tokamak. Density predictions based on line ratios of beryllium-, boron-, carbon-, nitrogen-, and oxygen-like calcium are compared with independent density measurements. Good agreement is found in the cases with minimal experimental uncertainties.

All computational data are available in electronic form upon request.

Acknowledgements

The authors would like to acknowledge the TEXT and FTU tokamak teams. This work was supported by U.S. DoE Grant DE-FG02-86ER53214 at JHU and Contract No. W-7405-ENG-48 at LLNL.