Fe XVII X-ray lines in solar coronal and laboratory plasmas

Theoretical intensities of the Fe XVII X-ray lines due to transitions 2p(6) - 2p(5)3d (near 15 Angstrom) and 2p(6) - 2p(5)3s (near 17 Angstrom) are presented, and compared with solar flare and active region spectra. The ratio of the 15 Angstrom lines to the 17 Angstrom lines is a function of temperature T-e, but for solar spectra this is not of practical use because of the resonance scattering of the intense 15.015 Angstrom line. Instead we use the ratio of a nearby Fe XVIII line to obtain T-e. We find very satisfactory correspondence between solar spectra and synthetic spectra based on calculated line intensities with appropriately chosen T-e apart from the 15.015 Angstrom line, which is sometimes less intense than its theoretical value, apparently owing to resonance scattering. Spectra emitted by DITE and JET tokamak plasmas with measured T-e and N-e, are also considered. A predicted density variation of the ratio of the Fe XVII lines at 17.051 Angstrom and 17.096 Angstrom is confirmed, and using Abel inversion techniques applied to a sequence of DITE spectra with different radial distances good agreement is found between the theoretical temperature variation of the I(15.015 Angstrom)/I(16.776 Angstrom) line ratio and that derived from these spectra. We conclude that our calculated Fe XVII line intensities are very reliable and may therefore be used in future analysis.