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Abstract

Understanding of the tungsten (W) behaviour during the plasma discharges in JET tokamak is fundamental for achieving stable discharge with low radiation losses. Moreover, its concentration has to be minimized to avoid plasma disruptions, which are particularly dangerous for larger tokamak devices. Unfortunately, the vast number of the possible excited states in W ions and the lack of relevant accurate photon emissivity coefficients for the electron temperatures below 2.5 keV hinder precise calculations and raises the demand for additional, machine-specific coefficients. The work presents the recent progress in development of the calibration method of the W radiated power and concentration from the measurements of the XUV spectrometer. It included finding W events in the low confinement mode with low admixture of mid-Z impurities, negligible rotation and sufficiently high electron temperature to ensure that the bulk radiated power estimated from bolometry system corresponds to the W radiated power. These conditions were met either after the successful laser ablation of the W target or spontaneously during the JET discharge. The enhancements in the fitting method together with new calibration factors and updated geometry of the line of sight of the XUV spectrometer provided satisfactory agreement of the calculated radiated power for W events with the former code calculating these values for the JET pulses <#90000 with improved stability of the calculations. For the JET pulses >#90000 the calibration factor remained at similar level, which has been confirmed by the long-term DiMPle analysis of the Be IV line. The aim of the work is to expand existing analyses done in previous works related to estimation of W concentration and radiated power with updated calibration and later combine it with SXR diagnostics, which will be used for the D-T discharges.