Experimental and simulatedargon 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 Jettokamak on a single null divertor configuration have been simulated. Thespectra include lines from five ionization states, namely from Ar15+Li-like to Ar11+ N-like ions. Collisional-radiative models have beenconstructed for these five Ar ions, considering electron collisionalexcitation and radiative decay as the populating processes of the excitedstates. These models give photon emission coefficients for the emittedlines at electron density and temperature values corresponding to theexperimental situations. Impurity modelling is performed using aone-dimensional (1D) impurity transport code, calculating thesteady-state radial distribution of the Ar ions. The Ar line brightnessesare evaluated in a post-processing subroutine and simulated spectra areobtained. The parts of the spectra corresponding to a single-ionizationstate do not depend on the experimental conditions and show goodagreement except for the amplitude of the simulated 2s-3p Ar XVIline and the shape of the simulated 2.50 nm feature (composed of Ar XVI and Ar XV lines). On the other hand, the superpositionof these spectra depends on the experimental conditions, as aconsequence of the fact that the ion charge distributiondepends not only on the radial profiles of the electrondensity and temperature, but also of the impurity transportcoefficients. Simulations of the Ar spectra (includingtransport) give confidence in the atomic physics calculations;moreover, they allow the determination of the transportcoefficients in the plasma region emitting the consideredionization states, i.e. at the interior of the last closedmagnetic surface (LCMS). For a correct simulation of theamplitudes of the spectral features it is necessary to includea transport barrier inside the LCMS. As far as the atomicphysics is concerned, we report improved wavelengths forAr XV transitions and we benchmark photon emissioncoefficients for XUV transitions in highly ionizedargon.