A Method for Determining the Concentrations of the C and Fe Impurities in the T-15MD Tokamak Discharges Using the Continuous Plasma Radiation Spectrum in the Visible and Soft X-Ray Regions

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A method is proposed to simultaneously determine the concentrations of atoms and ions of a heavy (iron, Fe) and a light (carbon, C) impurity in the T-15MD tokamak plasma. With auxiliary heating power for ions and electrons in the installation of ~15–20 MW, when fusion temperatures Ti ~ Te ~ 5–9 keV are reached at a density of ne ~ 1020 m–3, high amounts of impurity materials from the chamber wall (Fe) and protective carbon tiles (C) are expected to enter the tokamak discharge. These impurities can worsen the plasma conductivity and cause electron energy loss through radiation, having an extremely negative effect on the key plasma characteristics: its heating, confinement, and stability. Simultaneous measurements of the absolute values and spatial distributions of the intensity of the plasma radiation continuum in the visible (2.37 eV) and soft X-ray (2.65 keV) spectral ranges combined with measurements of electron temperature Te and plasma density ne profiles and magnetic surface distributions in the plasma column allow one to use the radiation–collisional or coronal models to determine the values and profiles of the C and Fe impurity concentrations and, consequently, monitor the concentrations of both impurities and their decrease.