Neutral helium line emission for edge plasma conditions F.B. Rosmej a, * , R. Stamm a , S. Fritzsche c , H. Capes b , M. Koubiti a , Y. Marandet a , V.S. Lisitsa d , N. Ohno e , S. Takamura f , D. Nishijima g a PIIM-UMR 6633 CNRS/Universite ´ de Provence, centre St-Je ´ro ˆ me, 13397 Marseille, France b DRFC, Association Euratom-CEA, 13108 Saint Paul lez Durance Cedex, France c Department of Physics, University Kassel, Heinrich-Plett-Str. 40, D-34132 Kassel, Germany d Russian Research Center ‘Kurchatov Institute’, 123182 Moscow, Russia e EcoTopia Science Institute, Nagoya University, Japan f Department of Energy Engineering and Science, Nagoya University, Japan g Max-Planck Institut fu ¨ r Plasmaphysik, D-85748 Garching, Germany Abstract A diagnostic method for the determination of the neutral helium diffusion coefficient in the edge of magnetically con- fined fusion plasmas is developed on the basis of emission spectroscopy and population kinetics. The new collisional- radiative numerical code SOPHIA showed that intercombination transitions are extremely important to describe the qualitative and quantitative behaviour of the line emission and the population flow in diffusive plasmas. Corresponding simulations relevant for edge plasma conditions and the NAGDIS-II plasma simulator are discussed. Ó 2004 Elsevier B.V. All rights reserved. PACS: 32.70.Fw; 52.55.Fa; 52.25.Rv; 52.25.Vy Keywords: Divertor plasma; Diffusion; Edge modelling; Radiation; Helium; Neutrals; JET; NAGDIS-II; Spectroscopy 1. Introduction Detached plasmas provide a promising method for reducing the heat flux of plasma facing components and their investigation is an important ITER design activity. Recombination processes are responsible for the plasma detachment and the spectroscopic investiga- tion of the corresponding radiation emission is therefore of great interest [e.g., [1–3]]. However, molecular recom- bination processes involved are very complex (e.g., vib- rationally excited hydrogen molecules) and it is desirable to avoid them as they are difficult to model. For this reason the analysis of the neutral helium emis- sion to probe edge plasma conditions is much more advantageous. The analysis of the radiation emission originating from the various elements and ionisation stages is of great interest, because it provides the possibility for a wide and unique characterization of the plasma: e.g., temperature, density, diffusion, charge exchange, fields, temporal and spatial variations, turbulence and fluctua- tion analysis. Moreover, a large impact from the spec- troscopic analysis stems from the fact, that it is based essentially on a collisional-radiative approach and there- fore provides a plasma model independent information. 0022-3115/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jnucmat.2004.10.141 * Corresponding author. E-mail addresses: rosmej@piima1.univ-mrs.fr (F.B. Ros- mej), roland.stamm@piimdgp.univ-mrs.fr (R. Stamm). Journal of Nuclear Materials 337–339 (2005) 1101–1105 www.elsevier.com/locate/jnucmat