Deuterium depth profiling in JT-60U tiles using the D(He, p)He resonant nuclear reaction

D(He, p)He核反応分析法を用いたJT-60Uタイルの重水素深さ分析

林 孝夫; 杉山 一慶*; Krieger, K.*; Mayer, M.*; Alimov, V. Kh.*; 田辺 哲朗*; 正木 圭; 宮 直之

Hayashi, Takao; Sugiyama, Kazuyoshi*; Krieger, K.*; Mayer, M.*; Alimov, V. Kh.*; Tanabe, Tetsuo*; Masaki, Kei; Miya, Naoyuki

D(He, p)He核反応分析法を用いてJT-60Uタイルを分析した。最も重水素濃度が高かったのは外側ドームウィングの排気スロット近傍であり、深さ16mまでの重水素の面密度は2.510 D/mであった。ここではミクロンオーダーの堆積層がタイル表面に観察されており、共堆積により多量の重水素量が蓄積したと考えられる。また中性粒子ビーム入射加熱(NBI)に起因する重水素が外側ドームウィングやドームトップタイルに高粒子束で入射し、重水素蓄積に寄与していると考えられる。深さ分布については約2.5mにD/C0.05の緩やかなピークがあった。これは大気解放前にプラズマ対向壁からトリチウムを除去するための軽水素放電により表面近傍の重水素が軽水素に置換したためである。一方、第一壁領域では最も重水素量の多いところで1.010 D/mであった。

The absolute concentrations and the depth profiles of deuterium in plasma-facing graphite tiles used in JT-60U were determined by means of the D(He, p)He resonant nuclear reaction. The highest deuterium concentration was found at a plasma-facing surface near the outer pumping slot on the outer dome wing tile, where redeposited layers with thicknesses in the micron or submicron range were observed, indicating deuterium codepostion with carbon. In addition, a high flux of high energy deuterium originating from NBI is expected on the outer dome wing as well as on the dome top tile, and could have some contribution to this area of highest deuterium retention. The deuterium content integrated up to about 16 m was 2.510 D/m. The depth profile has a broad peak in the atomic ratio of D/C0.05 at a depth of about 2.5 m. This is mainly because D retained in the top surface was replaced by H due to isotope exchange during H discharges, which were carried out to remove tritium from the plasma-facing wall before air ventilation. In erosion dominated areas such as the outer divertor tiles, the amount of deuterium was one order of magnitude lower than that on the outer dome wing tile. In the first wall area, the highest amount of deuterium with a content of 1.010 D/m was found in the upper region, nearest to the plasma. Again implantation of high energy deuterium due to NBI could have some contribution to the high deuterium retention.