Letter to the Editors Light emission from carbon-based materials under ITER relevant thermal shock loads T. Hirai a, * , J. Linke a , W. K€ uhnlein b , G. Sergienko c , S. Brezinsek c a IWV 2, Forschungszentrum J€ulich GmbH, EURATOM-Association, 52425 J€ulich, Germany b BZ Forschungszentrum J€ulich GmbH, EURATOM-Association, 52425 J€ulich, Germany c IPP Forschungszentrum J€ulich GmbH, EURATOM-Association, Trilateral Euregio Cluster, 52425 J€ulich, Germany Received 28 January 2003; accepted 21 March 2003 Abstract Light emission from carbon-based materials (fine grain graphite, CFC and silicon doped CFC) was observed during ITER relevant thermal shock loads by means of in situ optical diagnostics. The light emission which corresponds to particle release clearly indicated different particle release processes in the three materials. The differences were also found in the initiation temperatures of particle release and the surface morphology of the loaded areas. These results are related to the thermal stress in bulk materials. In addition to particle release, vapor cloud formation caused by thermal shock loads were observed as CII lines and lines from the C 2 Swan system. No Si lines but lines from SiC 2 molecules (Merrill–Sanford bands) were observed in Si doped CFC. This indicates that atomic silicon is not released under ITER relevant thermal shock loads. Ó 2003 Elsevier B.V. All rights reserved. 1. Introduction Thermal shock loads of the order of a few 10 MJ/m 2 in several ms (disruptions) and about 60 MJ/m 2 in sev- eral hundred ms (vertical displacement events (VDEs)) are expected in the International Thermonuclear Ex- perimental Reactor (ITER) [1]. Armor materials will be strongly eroded under these conditions, therefore, the materialsÕ R&D under these transient power loads still remains as one of the most challenging issues associating with the lifetime of the armor materials. Since carbon-based materials have a high thermal shock resistance and, additionally, carbon fiber com- posites (CFCs) show high thermal conductivity (up to 350 W/m K), they were selected as candidate plasma facing armor materials in ITER [2]. However, recent studies show a strong erosion of carbon-based materials due to particle release (Fig. 1) caused by brittle de- struction during thermal shock loads [3–7]. Therefore, it is important to study the material behavior under in- tense thermal loads. In the present work, the light emission from carbon- based materials was studied by optical diagnostics under ITER relevant disruption conditions. 2. Experimental ITER relevant thermal shock loads were applied with an energetic electron beam in the electron beam facility, JUDITH. The details of the facility are described else- where [8]. Three carbon-based materials: fine grain graphite (R6650, SGL Carbon-Ringsdorff), CFC (NB31, SNECMA Motors) and silicon doped CFC (NS31, SNECMA Motors) with dimensions of 25  25  10 mm 3 , were loaded by electron beam (120 keV, U  1 mm) at room temperature in vacuum (<10 4 Pa). * Corresponding author. Tel.: +49-2461 615843; fax: +49- 2461 613699. E-mail address: t.hirai@fz-juelich.de (T. Hirai). 0022-3115/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0022-3115(03)00198-3 www.elsevier.com/locate/jnucmat Journal of Nuclear Materials 321 (2003) 110–114