Observations and comparisons with theory of the heliumlike and hydrogenlike resonance lines and satellites of nickel from the JET tokamak

Abstract

The resonance lines and heliumlike to boronlike satellites of heliumlike nickel and the Lyman-α doublet and heliumlike satellites of hydrogenlike nickel emitted from the JET tokamak have been recorded with good spectral resolution (λ/Δλ=20 000). Atomic data (wavelengths and intensity factors) for the dielectronic and other satellites are calculated in a multiconfiguration intermediate-coupling scheme with use of scaled Thomas-Fermi-Dirac potentials and compared with the experimental spectra. Overall good agreement between theory and the experimental spectra is obtained, though the intensities of satellites to the heliumlike lines indicate that the populations of the lithiumlike to boronlike ions relative to the heliumlike populations are greater than expected for a coronal ionization balance. Possible causes of this discrepancy are departures from coronal equilibrium due to charge exchange with neutral hydrogen atoms or departures from coronal equilibrium due to transport of lower ionization stages of nickel impurities from the tokamak edge to the center at a rate greater than predicted by other diagnostics.