Satellite spectra of the K alpha resonance line of heliumlike nickel, Ni XXVII, from tokamak-fusion-test reactor plasmas: Comparison between theory and experiment.

Abstract

Satellite spectra of the K\ensuremath{\alpha} line of heliumlike nickel, Ni xxvii, recorded from tokamak-fusion-test reactor (TFTR) Ohmic plasmas with well-defined experimental conditions and central electron temperatures in the range 2--5 keV, have been compared with theoretical predictions. The relevant plasma parameters that determine the spectral features, i.e., the electron and ion temperatures, and the relative abundances of Ni xxv, Ni xxvi, and Ni xxvii have been obtained from least-squares fits of synthetic spectra to the experimental data. Both the dielectronic satellites and the satellites which are produced by collisional inner-shell excitation are well described by the theory given by Bombarda et al. [Phys. Rev. A 37, 504 (1988)] and Vainshtein and Safronova (unpublished). The electron-temperature results derived from the fits are in good agreement with electron-temperature measurements from independent diagnostics. However, the values obtained for the relative abundances of Ni xxv, Ni xxvi, and Ni xxvii are larger by factors of 1.3--2 compared to recent coronal-equilibrium predictions of Zastrow, K\"allne, and Summers [Phys. Rev. A 41, 1427 (1990)]. Plasma-modeling calculations performed with the multi-ion-species-transport [R. A. Hulse, Nucl. Technol. Fusion 3, 259 (1983)] code show that these deviations can be explained by radial ion transport assuming for the ion-transport diffusion coefficient D values in the range 1--2.5 ${\mathrm{m}}^{2}$ ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$.However, the observed deviations may be partially ascribed to theoretical uncertainties of the ionization and recombination rate coefficients used for the coronal-equilibrium calculations. Systematic discrepancies are found to exist between the predicted and observed intensity ratios, x/w, y/w, and z/w, of the heliumlike lines w, 1${\mathit{s}}^{2}$ $^{1}$${\mathit{S}}_{0}$--1s2p $^{1}$${\mathit{P}}_{1}$; x, 1${\mathit{s}}^{2}$ $^{1}$${\mathit{S}}_{0}$--1s2p $^{3}$${\mathit{P}}_{2}$; y, 1${\mathit{s}}^{2}$ $^{1}$${\mathit{S}}_{0}$--1s2p $^{3}$${\mathit{P}}_{1}$; and z, 1${\mathit{s}}^{2}$ $^{1}$${\mathit{S}}_{0}$--1s2s $^{3}$${\mathit{S}}_{1}$.