HIGH-RESOLUTION MEASUREMENTS, LINE IDENTIFICATION, AND SPECTRAL MODELING OF K-ALPHA TRANSITIONS IN FE-XVIII-FE-XXV

A detailed analysis of the iron Kalpha emission spectrum covering the wavelength region from 1.840 to 1.9 angstrom is presented. Measurements are made with a high-resolution Bragg crystal spectrometer on the Princeton Large Torus (PLT) tokamak for plasma conditions which closely resemble those of solar flares. A total of 40 features are identified, consisting of either single or multiple lines from eight charge states in iron, Fe XVIII-Fe XXV, and their wavelengths are determined with an accuracy of 0.1-0.4 mangstrom. Many of these features are identified for the first time. In the interpretation of our observations we rely on model calculations that determine the ionic species abundances from electron density and temperature profiles measured indePendently with nonspectroscopic techniques and that incorporate theoretical collisional excitation and dielectronic recombination rates resulting in the excitation of the ls2s(r)2p(s) configurations. The model calculations also include the effect of diffusive ion transport. Good overall agreement between the model calculations and the observations is obtained, which gives us confidence in our line identifications and spectral modeling capabilities. The results are compared with earlier analyses of the Kalpha emission from the Sun. While many similarities are found, a few differences arise from the somewhat higher electron density in tokamak plasmas (10(13) cm-3), which affects the fine-structure level populations of the ground states of the initial ion undergoing electron-impact excitation or dielectronic recombination. We also find that several spectral features are comprised of different transitions from those reported in earlier analyses of solar data.