Neutral beam stopping and emission in fusion plasmas I: deuterium beams

The charge transfer reaction of neutral deuterium beams with impurities enables one of the principle quantitative diagnostic measurements of the hot core fusion plasma; that is, charge exchange spectroscopy. The complementary measurement of beam emission spectroscopy has been fruitful in motional Stark wavelength shift and fluctuation studies, but less so in using absolute measured intensities. In the last two years we have achieved substantial improvement in the quantitative analysis and agreement between the observed and modelled beam emission at the JET Joint Undertaking. This has depended on improved spectral fitting of the overlayed Dα motional Stark multiplet, self-consistent beam emission and impurity charge exchange modelling and analysis, and revision of the data entering the modelling of the beam emission process. The paper outlines the present JET beam emission diagnostic system and the collisional radiative modelling of deuterium beam stopping and emission. The nature and organization of the effective derived data directly used in experimental interpretation at JET are described and some results of spectral analysis of deuterium beam emission given. The practical implementation of the methods described here is part of the ADAS Project.