TEM and EELS characterization of carbon dust and co-deposited layers from the TEXTOR tokamak S. Muto a, * , T. Tanabe a , A. Hirota b , M. Rubel c , V. Philipps d , T. Maruyama e a Center for Integrated Research in Science and Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan b Graduate School of Nuclear Engineering, Nagoya University, Chikusa-ku, Nagoya 464-8603, Japan c Alfv en Laboratory, Royal Institute of Technology, Association EURATOM-VR, S-100 44 Stockholm, Sweden d Institute of Plasma Physics, Forschungszentrum J€ ulich, Association, EURATOM, Trilateral Euregio Cluster (TEC), 52425 J€ ulich, Germany e The Wakasawan Energy Research Center, Tsuruga 914-0192, Japan Abstract Co-deposited layers and dust agglomerates formed at TEXTOR tokamak were collected and examined in detail by means of transmission electron microscopy and electron energy-loss spectroscopy. The analysis has shown that thick deposits and dust contain mainly carbon with an admixture of boron precipitates and small amounts of other elements. The carbon deposit was mostly amorphous, while strips were graphite crystallites embedded in dust agglomerates. In thin co-deposits on the collector probe very small graphite crystallites were piled up with a preferential orientation. The results are discussed in terms of processes decisive for the erosion of plasma facing components and for the fuel re- tention. Ó 2002 Elsevier Science B.V. All rights reserved. 1. Introduction The formation of co-deposited layers on plasma facing materials in a D-T burning machine derives from plasma–material interactions, such as erosion, ioniza- tion, transport, charge-exchange and co- or re-deposi- tion. Therefore, the layers ÔbearÕ the information on these complex processes. As a result, the structure of co- deposits depends on the temperature of the substrates and their position relative to the plasma configuration in a torus, and on energy, flux and angle of incidence of incoming ions. In addition, the wall conditions in the machine are particularly important for the dust forma- tion. It is known that hydrogen retention or absorption in graphite is highly related to the structure of carbon materials [1–3]. In general, the more the structure is disordered, the higher hydrogen retention occurs. These facts motivate us to conduct a detailed structural anal- ysis of co-deposited layers. In our previous prelimi- nary work we reported the analyses of layers formed on a graphite tile of the toroidal belt limiter (ALT-II) of TEXTOR [4]. Studies carried out by means of transmission electron microscopy (TEM) and electron energy-loss spectroscopy (EELS) revealed that the layer consisted of amorphous graphitic carbon containing a high density of crystalline boron precipitates and a detectable amount of oxygen. The structure is very similar to the one observed for B-doped graphite irra- diated by H þ . The considerable amount of boron comes from routinely employed boronization, and oxygen from the plasma itself, which contains about 3% oxygen as an impurity. In the present study we have extended the previous analysis to other carbon residues from several plasma facing components in the TEXTOR tokamak, such as the deposited layer from other limiter tiles, dust agglomerates collected from the device floor and thin co-deposits grown on a surface of the collector probe exposed to the scrape- off layer plasma. Based on the detailed structural analysis, Journal of Nuclear Materials 307–311 (2002) 1289–1293 www.elsevier.com/locate/jnucmat * Corresponding author. Tel.: +81-52 789 5200; fax: +81-52 789 5158. E-mail address: muto@cirse.nagoya-u.ac.jp (S. Muto). 0022-3115/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. PII:S0022-3115(02)01118-2