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 Angstr om) are presented, and compared with solar flare and active region spe ctra. 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 pra ctical use because of the resonance scattering of the intense 15.015 A ngstrom line. Instead we use the ratio of a nearby Fe XVIII line to ob tain T-e. We find very satisfactory correspondence between solar spect ra and synthetic spectra based on calculated line intensities with app ropriately chosen T-e apart from the 15.015 Angstrom line, which is so metimes less intense than its theoretical value, apparently owing to r esonance scattering. Spectra emitted by DITE and JET tokamak plasmas w ith measured T-e and N-e, are also considered. A predicted density var iation 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 agree ment is found between the theoretical temperature variation of the I(1 5.015 Angstrom)/I(16.776 Angstrom) line ratio and that derived from th ese spectra. We conclude that our calculated Fe XVII line intensities are very reliable and may therefore be used in future analysis.