C material will be used as a plasma facing material of the divertor target plates in ITER. The use comes from a great advantage that C material has a high thermal shock resistance. For the use, however, there is a crucial issue: chemical erosion of the material by the D plasma exposure occurs easily, which indicates a significant release of hydrocarbons such as CD₄ and C₂D₄ to the core plasmas [1]. From two viewpoints of contamination of the core plasmas and net erosion of the material, how the chemically eroded hydrocarbons change the local C impurity transport and the resultant net erosion needs to be investigated enough.
In this study, effects of chemically eroded CD₄ and C₂D₄ molecules on local penetrations of C⁺, C²⁺ and C³⁺ impurities to the core plasma have been investigated using a Monte-Carlo simulation. In the simulation, CD₄ and C₂D₄ reaction rate coefficients for e^- impact ionization, dissociation, dissociative recombination and D⁺ impact charge transfer are used [2, 3]. The result has been compared with experimental data [4]. Also, the effects on the net erosion rates for different plasma parameters and for the designed ITER divertor plasma condition [5] have been investigated. The paper describes and discusses how the local C impurity penetrations and the net erosion rates are changed under the influence of the chemically eroded molecules.
The calculated C¹⁺ emission profile at T_eLCFS= 30 eV and n_e= 10¹² cm^-3 reproduces the measured CII light emission profile [4]. The agreement indicates that the contribution of CD₄ is stronger than that of C₂D₄ near the target. For the C²⁺ and C³⁺ profiles, however, the opposite results occur, which indicates the significant contribution of C₂D₄ near the target. At T_eLCFS= 3 eV and n_e= 10¹³ cm^-3, which corresponds to the detached plasma condition, there is the influence of the charge transfer reactions of C_xD_y with D⁺. By the charge transfer reactions, the penetrations are suppressed. In particular, for CD₄ it is more pronounced. For the net erosion rate, there is also the influence of the charge transfer reactions, by which the local redeposition for CD₄ and C₂D₄ is enhanced.

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