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Chemical Binding States of Carbon Atoms Migrated in Tungsten Coating Layer Exposed to JT-60U Divertor Plasmas

Masakatsu FUKUMOTO, Tomohide NAKANO, Yoshio UEDA¹⁾ and Kiyoshi ITAMI

Japan Atomic Energy Agency, Naka, Ibaraki 311-0193, Japan

1)

Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871, Japan

(Received 5 July 2013 / Accepted 13 September 2013 / Published 15 November 2013)

Abstract

Carbon migration in the tungsten coating layer exposed to JT-60U divertor plasmas has been investigated by analysis of chemical binding states of the carbon atoms. More than 1% of carbon atoms were accumulated as graphitic carbon, amorphous carbon and/or carbon-deuterium bonds. This concentration was more than five orders of magnitude higher than the solubility of carbon atoms in tungsten lattice. Up to 20% of ditungsten carbide (W₂C) was also formed in the tungsten coating layer. These findings suggested the following carbon migration mechanism in the tungsten coating layer. The incident carbon migrates along grain boundaries and defects such as pores over the depth which is evaluated by the carbon diffusion coefficient in tungsten lattice. The carbon atoms trapped on grain surface penetrate and diffuse in the grains. The carbon atoms exceeded the solubility of carbon atoms in tungsten lattice chemically bind to tungsten atoms and form W₂C.

Copyright (c) 2013 The Japan Society of Plasma Science and Nuclear Fusion Research

Keywords

tungsten, carbon, tritium retention, mixed material, JT-60U

DOI: 10.1585/pfr.8.1405159

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This paper may be cited as follows:

Masakatsu FUKUMOTO, Tomohide NAKANO, Yoshio UEDA and Kiyoshi ITAMI, Plasma Fusion Res. 8, 1405159 (2013).