Extreme Ultraviolet Emission Lines of ca xv in Solar and Laboratory Spectra

New R-matrix calculations of electron impact excitation rates in Caxv are used to derive theoretical electron density diagnostic emission line intensity ratios involving 2s²2p²–2s2p³ transitions, specifically R₁=I(208.70 Å)/I(200.98 Å), R₂=I(181.91 Å)/I(200.98 Å), and R₃=I(215.38 Å)/I(200.98 Å), for a range of electron temperatures (T_e=10^6.4–10^6.8 K) and densities (N_e=10⁹–10¹³ cm^–3) appropriate to solar coronal plasmas. Electron densities deduced from the observed values of R₁, R₂, and R₃ for several solar flares, measured from spectra obtained with the Naval Research Laboratory's S082A spectrograph on board Skylab, are found to be consistent. In addition, the derived electron densities are in excellent agreement with those determined from line ratios in Caxvi, which is formed at a similar electron temperature to Caxv. These results provide some experimental verification for the accuracy of the line ratio calculations, and hence the atomic data on which they are based. A set of eight theoretical Caxv line ratios involving 2s²2p²–2s2p³ transitions in the wavelength range 140–216 Å are also found to be in good agreement with those measured from spectra of the TEXT tokamak plasma, for which the electron temperature and density have been independently determined. This provides additional support for the accuracy of the theoretical line ratios and atomic data.