Determination of isotope ratio in the divertor of JET-ILW by high-resolution H alpha spectroscopy: H-D experiment and implications for D-T experiment

The data of the H alphahigh-resolution spectroscopy, collected on the multiple lines of sight, which cover the entire divertorspace in poloidal cross-section, during the recent hydrogen- deuteriumexperiments in JET-ILW (ITER-like wall), are processed. A strong spatial inhomogeneity of the hydrogen concentration, H/(H + D), in divertoris found in many pulses. Namely, the H/(H + D) ratio may be lower in the inner divertorthan that in the outer divertorby the values of 0.15-0.35, depending on the conditions of gas puffing and plasma heating. This effect suggests the necessity of spatially-resolved measurements of isotope ratio in the divertorin the upcoming deuterium- tritiumexperiments. Also, separation of the overlapped T alpha and D alpha spectral linesis shown to be a challenging task especially when the local Doppler-broadened(Gaussian) line shapes are noticeably distorted by the net inward flux of fast non-Maxwellian neutral atoms. We use the respective, formerly developed model of an asymmetric spectral line shape, while analysing the data of the first deuterium- tritiumexperiment in JET-C (carbon wall), and test the model via comparing the isotope ratio results with another diagnostic's measurements. This model is shown to increase the accuracy of tritiumconcentration measurements in the divertor.