Boronization effects using deuterated-decaborane (BD) in JT-60U

Nakano, Tomohide; Higashijima, Satoru; Kubo, Hirotaka; Yagyu, Junichi; Arai, Takashi; Asakura, Nobuyuki; Itami, Kiyoshi

In JT-60U, boronization using hydride-decaborane (BD) was performed to reduce oxygen impurity and particle recycling. A problem of the boronization was that hydrogen originating from hydride-decaborane diluted core deuterium plasmas. In order to minimize the number of conditioning tokamak discharges, boronization using deuterated-decaborane (BD) has been introduced recently. In order to investigate durability of the boronization effects, discharges with an identical condition were repeated. Boronization using 20 g of deuterated-decaborane could reduce a core oxygen content from 1.9% to only 1.3% in L-mode discharges with a neutral beam heating power of 4 MW. Boronization using 70 g of deuterated-decaborane reduced the core oxygen content from 2.2% to 0.5%. After the boronization using 70 g of deuterated-decaborane ( thickness of the Boron layer 135 nm ), the core oxygen content increased gradually from 0.5% to 1% in 400 shots.