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A noninvasive diagnostic technique relying on optical emission spectroscopy is used for studying plasma confined in a purely toroidal magnetic field. Visible emission lines of molecular hydrogen were specifically targeted. Bi-dimensional structures and poloidal plasma profiles were reconstructed from the emissivity distribution of hydrogen Fulcher system using a tomographic method. A few details concerning the methods employed to capture different emission viewlines, data reduction and tomographic reconstruction techniques are also addressed. We report also the first measurement of the excitation temperature of the $$\text {H}_2$$ H 2 [3c] level in the center of the plasma column, $$T_{\mathrm{exc}}=0.67 \pm 0.11$$ T exc = 0.67 ± 0.11 eV. Graphic Abstract

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