Inner-shell x-ray line spectra of highly ionized titanium, chromium, iron, and nickel and their application to laboratory plasmas

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Abstract
The intensities of x‐ray lines due to inner‐shell 1s‐2p transitions in O i‐, N i‐, and C i‐like ions of Ti xv–xvii, Cr xvii‐xix, Fe xix‐xxi, and Ni xxi‐xxiii seen in tokamak plasmas are calculated. The lines are assumed to be formed by dielectronic recombination and inner‐shell excitation. The present calculations are an extension of previous work for iron alone. The dielectronic contribution for iron was found to be more important, and this is true for the ions of titanium, chromium, and nickel considered here. The dielectronic rates were calculated using a suite of computer programs developed by one of us. The inner‐shell contribution was estimated by van Regemorter’s formula. The considered ion stages have two or more fine‐structure levels in the ground configuration, which gives rise to a density dependence of both dielectronic and collision excitation mechanisms at densities between 1011 and 1016 cm−3, a range suitable for tokamak plasmas. A means for determining the density of high‐temperature plasmas is presented for when no other density diagnostics are available. Finally, the present calculations were applied to the problem of radial ion diffusion in tokamaks. Spectra were calculated by integrating along various lines of sight to simulate what might be observed by an actual spectrometer viewing a tokamak plasma. The assumed temperature and density profiles and two diffusion models were taken from a recent calculation. A method for determining the diffusion coefficient from tokamak observations is discussed.