Experimental and simulated argon spectra in the 2.3-3.4 nm region from tokamak plasmas

Abstract

Experimental argon spectra in the 2.3-3.4 nm region from the Jet tokamak on a single null divertor configuration have been simulated. The spectra include lines from five ionization states, namely from Ar15+ Li-like to Ar11+ N-like ions. Collisional-radiative models have been constructed for these five Ar ions, considering electron collisional excitation and radiative decay as the populating processes of the excited states. These models give photon emission coefficients for the emitted lines at electron density and temperature values corresponding to the experimental situations. Impurity modelling is performed using a one-dimensional (1D) impurity transport code, calculating the steady-state radial distribution of the Ar ions. The Ar line brightnesses are evaluated in a post-processing subroutine and simulated spectra are obtained. The parts of the spectra corresponding to a single-ionization state do not depend on the experimental conditions and show good agreement except for the amplitude of the simulated 2s-3p Ar XVI line and the shape of the simulated 2.50 nm feature (composed of Ar XVI and Ar XV lines). 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 the electron density and temperature, but also of the impurity transport coefficients. Simulations of the Ar spectra (including transport) give confidence in the atomic physics calculations; moreover, they allow the determination of the transport coefficients in the plasma region emitting the considered ionization states, i.e. at the interior of the last closed magnetic surface (LCMS). For a correct simulation of the amplitudes of the spectral features it is necessary to include a transport barrier inside the LCMS. As far as the atomic physics is concerned, we report improved wavelengths for Ar XV transitions and we benchmark photon emission coefficients for XUV transitions in highly ionized argon.

Spectral Line Shapes as a Diagnostic Tool in Magnetic Fusion

“…For this simulation both transport coefficients are the same as for the Ar seeded discharge of Ref. [21], implying, as found in several JET spectroscopic data analysis, the presence of a peripheral transport barrier, obtained reducing D and/or increasing V inward. The lack of other experimental spectroscopic data and/or of time resolved spectra hinders any verification of the used atomic data.…”

“…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.…”

“…on the determination of the electron temperature, electron density and elemental abundances. In most cases atomic data are supposed to be valid and the simulations give D(r) and V(r), like, e.g., in Refs [20,21]. But with high quality and large amount of spectroscopic data, it is possible to go further and to verify also S ion and α rec .…”

“…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.…”

Identification and analysis of soft X-ray lines of Ar xiii-Ar xvi in laboratory and astrophysical plasmas

“…Not only the intense lines of 3d–2p transitions, but also 4d–2p or even 5d–2p lines were observed in their experiment. Mattioli et al (2001) analysed the experimental spectra of argon in the wavelength range 23–34 Å from jet tokamak plasmas, and simulated them using collisional–radiative models constructed for Ar xii –Ar xvi ions. To interpret these plasma spectra, one needs atomic data within n = 4 or even n = 5 configurations.…”