Long term hydrogen retention in the plasma facing carbon tiles of JT-60U

Abstract In order to investigate how fuel (H + D) retention increases with discharge time, we have measured long term H + D retention of the carbon tiles exposed to plasmas in JT-60U by TDS and SEM. The H + D retention in the re-deposited carbon layers on divertor tiles linearly increases with the thickness of the re-deposited layers with a constant hydrogen concentration of (H + D)/C ∼ 0.013. The C-deposition and H + D retention rates are in the order of ∼1 × 10 20  C/m 2 /s and ∼3.8 × 10 18 H + D atoms/m 2 /s, respectively. The H + D retentions in the near surface regions of eroded tiles both at outer divertor and outer first wall did not go over 5 × 10 22 H + D atoms/m 2 , suggesting hydrogen saturation at the near surface regions. However, in a little deeper region of the outer first wall tiles, direct implantation of energetic D originated from Neutral Beam Injection (NBI) caused gradual increase of the retention until saturation in the implanted depth.