Influence of the ICWC-driven isotope exchange pulses on the hydrogen/deuterium ratio in the boron layer at WEST

In this contribution, estimates are presented of the isotopic composition of the hydrogenic fuel retained in WEST boronized vessel wall during first tests of the isotope exchange from D to H and back via ion cyclotron wall conditioning pulses. An optical emission spectroscopy method of measuring the ratio of the boron hydride and boron deuteride molecular bands is proposed to estimate the influence of conditioning pulses on wall inventory. This method, contrary to the ordinary methods of isotope ratio estimation—residual gas analysis (RGA) or emission spectroscopy of hydrogen isotopes—provides the isotope ratio in the external layers of the wall, not in bulk plasma or in the exhaust. As the molecules are created during plasma-surface interactions and their isotopic composition depends on the hydrogen wall inventory, they are an unique possibility of probing this part of isotope exchange. The method is local, because the molecules dissociate relatively quickly in the plasma, so not only gradual isotope ratio changes in time but also their spatial distribution in toroidal and poloidal directions are presented in this contribution. Results of (Formula presented) (Formula presented) at the same time were within (Formula presented) (Formula presented) percentage points in all measured locations, which suggests good uniformity of the isotope exchange during wall conditioning plasma. The results are compared with RGA and hydrogen line emission spectroscopy data, showing the differences between the wall, bulk plasma and gas exhaust isotope content.