Chemical binding states of carbon atoms migrated in tungsten coating layer exposed to JT-60U divertor plasmas

JT-60Uダイバータプラズマに曝されたタングステン被覆層に進入した炭素原子の化学結合状態

福本 正勝; 仲野 友英; 上田 良夫*; 伊丹 潔

Fukumoto, Masakatsu; Nakano, Tomohide; Ueda, Yoshio*; Itami, Kiyoshi

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, disordered 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 (WC) was also formed in the tungsten coating layer. These findings suggested that the following carbon migration mechanism in the tungsten coating layer. The incident carbon atoms and hydrocarbon molecules migrate within 2.5 m in depth along grain boundaries and defects such as pores. The carbon atoms trapped to grain surfaces 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 WC.