Experimental and simulated M-shell nickel spectra in the 14.4–18.0 nm region from magnetic fusion devices

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 Ni 9+ to P-like Ni 13+ ions. For the JET limiter configuration the spectrum upper wavelength limit was higher (18.0 nm) and lines from Si-like Ni 14+ 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 lines 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

Atomic data for astrophysics: Ni XII

“…Nickel lines are also prominent in fusion plasma (see, e.g. Mattioli et al 2004). Accurate atomic data are needed for this ion.…”

Dielectronic recombination of argon-like ions

“…Nickel is one of the most important heavy impurities in tokamaks and early attempts by the TFR Group (1980) to model the fractional abundance of its charge states suffered from deficient DR data. Recent simulations of the observed plasma emission from magnetic confinement fusion devices, namely the JET tokamak in Abingdon and RFX in Padova (Mattioli et al 2004), also lacked accurate recombination rate coefficients for the Ni xi ion. However, reliable electron impact ionization data of the remaining ions in the nickel isonuclear sequence have been provided by Pindzola et al (1991) and were widely used by Mattioli et al (2004) in simulations of Ni emission line spectra.…”

Spectral Line Shapes as a Diagnostic Tool in Magnetic Fusion

“…[26] for Ge, the F-like to B-like charge states could not be simulated unless the relevant α rec /S ion ratios were increased. In another paper on M-shell Ni spectra in the 144-180 Å region [23] both D(r) and V(r) were known from similar discharges and with best fits on the strongest lines of the involved Ni X-XV ions, the best sets of data for both ionisation and recombination have been obtained.…”

“…Until recently, simulations of full spectra were less frequent. These include, e. g., full simulation in the XUV range of n=2 to n=2 L-shell Ne, Ar and Fe spectra [18,19], of n=3 to n=2 L-shell Ne and Ar spectra [20,21], and of n=3 to n=3 M-shell Fe and Ni spectra [22,23]. The analysis of spectra emitted by hot and well-diagnosed magnetic fusion plasmas is important since it touches on atomic physics issues to be used in the analysis of high spectral resolution astrophysical observations, i.e.…”

“…After evaluation of radial CSD, post-process subroutines are used to produce simulated spectra, using line photon emission coefficients (PECs) from collisionalradiative models (CRM). Like for Refs [18][19][20][21][22][23], the PECs have been obtained using the HULLAC code.…”