Hydrogen retention and carbon deposition in plasma facing wall and shadowed area of JT-60U

Masaki, Kei; Tanabe, Tetsuo*; Hirohata, Yuko*; Oya, Yasuhisa*; Shibahara, Takahiro*; Hayashi, Takao; Sugiyama, Kazuyoshi*; Arai, Takashi; Okuno, Kenji*; Miya, Naoyuki

Evaluation of fuel inventory and its retention process are critical issues for a next-step fusion device, especially with carbon-based wall. In order to resolve the issues, the hydrogen retention and carbon deposition analyses for the plasma facing surfaces and plasma-shadowed area of JT-60U have been performed. In JT-60U, erosion/deposition analyses for the plasma facing wall have shown that deposition was dominant at the inner-middle first wall and the inner divertor, whereas erosion dominant at the upper first wall and the outer divertor. Assuming toroidal symmetry in the erosion and deposition patterns, the net carbon erosion and deposition in the divertor area were estimated to be 0.34 kg and 0.55 kg, respectively. In a whole, the increment of carbon in the divertor region was 0.21 kg, which should be originated from the first wall. The hydrogen concentration in the thick deposition layer of the inner divertor was 0.02 in (H+D)/C. In the plasma-shadowed area underneath the divertor region at around 420 K, re-deposited layers of 2m-thick were found with high hydrogen concentration of 0.8 in (H+D)/C. The carbon deposition rate in the plasma-shadowed area, however, was 810 atoms/s, which was one order smaller than that (610 atoms/s) on the wall surface.