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- Mattioli, M, et al.
(author)
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Experimental and simulated M-shell nickel spectra in the 14.4-18.0 nm region from magnetic fusion devices
- 2004
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In: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 37:1, s. 13-40
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Journal article (peer-reviewed)abstract
- Experimental M-shell nickel spectra in the 14.4-16.5 nm region from the JET tokamak (from both divertor and limiter configurations) and from the reversed field pinch RFX have been simulated. These spectra include lines from five ionization states, namely from K-like N-i9+ to P-like Ni13+ ions. For the JET limiter configuration the spectrum upper wavelength limit was higher (18.0 nm) and lines from Si-like Ni14+ ions were also observed. Collisional-radiative (CR) models have been built for these six Ni ions, considering electron collisional excitation and radiative decay as the main populating processes for the excited states. These models give photon emission coefficients (PECs) for the emitted tines at electron density (n(e)) and temperature (T-e) values corresponding to the experimental situations. Impurity modelling is performed using a 1D impurity transport code, calculating the steady state radial distribution of the Ni ions. The Ni line brightnesses are evaluated in a post-processing subroutine and simulated spectra are obtained. The spectrum from a single ion, in the absence of blendings, depends only on the T-e and n(e) values in the emitting shell of the ionization state considered. On the other hand, the superposition of these spectra depends on the experimental conditions, as a consequence of the fact that the ion charge distribution depends not only on the radial profiles of T-e and n(e) but also on the chosen ionization and recombination rate coefficients and on the radial profiles of the impurity transport coefficients in the region of the emitting shells. Since the aim of the paper is the investigation of the atomic physics of the M-shell ions, the section discussing the plasma physics phenomena is purposely limited. For each experimental spectrum a few simulations are presented, since a unique choice has not been found by selecting the input parameters of the transport code. The effect of the T-e and n(e) values on the emitting shells as well as the influence of line blendings on the single-ionization-degree spectra are stressed. These, in turn, are then compared with the predictions. For the n(e) range considered the PECs are practically independent of n(e). The T-e dependence is much reduced due to the fact that the spectral fits performed are actually comparisons of line ratios. The agreement found between experimental and simulated single-ionization-degree spectra gives confidence in the atomic data used in the CR models.
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