Molecular deuterium sources in the outer divertor of JET A. Pospieszczyk b, * , S. Brezinsek b , G. Sergienko b , P.T. Greenland c , A. Huber b , A. Meigs a , Ph. Mertens b , U. Samm b , M. Stamp a , S. Wiesen b a UKAEA/EURATOM Fusion Association, Culham Science Centre, Abingdon, Oxon. OX14 3DB, UK b Institut fu ¨ r Plasmaphysik, Forschungszentrum Ju ¨ lich GmbH, EURATOM Association, Trilateral Euregio Cluster, D-52425 Ju ¨ lich, Germany c Optics Section, Blackett Laboratory, Imperial College, London SW7 2BZ, UK Abstract At JET the properties of deuterium molecules and their contribution to the total deuteron flux in the outer divertor for the horizontal configuration in L- and H-mode conditions have been determined. For this purpose the outer diver- tor was observed with several high resolution spectrometers and lines of sight directed vertically with spatial resolution from the outer vertical target plate to the centre of the MK IIB GB/SRP divertor. The rovibrational population of the Fulcher bands of the deuterium molecules could both be measured for the first five diagonal vibrational transitions. A collisional-radiative model for deuterium molecules was used to convert the measured photon fluxes into local molec- ular D 2 -fluxes. With more than 70% of the total proton flux originating from molecular sources molecules make up a significant contribution to the fuelling in the divertor. This was found to be in agreement with the 2d-fluid/neutral par- ticle code EDGE2D/NIMBUS. Ó 2004 Elsevier B.V. All rights reserved. PACS: 33.20.t; 33.20.Vq; 34.50.Dy; 52.25.Rv Keywords: Hydrogen; JET; Molecular effects; Recycling; Spectroscopy 1. Introduction Since the detection of major fractions of hydrogen/ deuterium molecules in front of limiters and in divertors with graphite surfaces via molecular spectroscopy [1–3], a growing attention has been devoted to the investiga- tion of the interplay between atoms, molecules and their interaction with the surrounding surfaces and to the study of the resulting particle energies. On TEXTOR [2,4–7] the atom to molecule ratio and the subsequent energy distribution have been measured, on ASDEX-U [3] the contribution of deuterium molecules to recombi- nation has been determined and on Tore-Supra [8] the potential of hydrogen/deuterium molecular spectros- copy for plasma diagnostics has been tested. The meth- ods employed in those devices have now been used to determine the location and the strength of molecular sources in the outer divertor of JET, where a number of high resolving spectrometers are available. 2. Diagnostics and methods Fig. 1 shows the lines of sight of the different views into the JET outer divertor. An overview spectrometer (KS3A, resolution  3000) observes the whole outer 0022-3115/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jnucmat.2004.09.061 * Corresponding author. E-mail address: a.pospieszczyk@fz-juelich.de (A. Pospiesz- czyk). Journal of Nuclear Materials 337–339 (2005) 500–504 www.elsevier.com/locate/jnucmat