Boronization using deuterated-decaborane in JT-60U

In JT-60U, boronization using hydride-decaborane (B₁₀H₁₄) vaporization has been conducted for the first wall conditioning. Compared to other discharge cleaning, boronization is claimed to be efficient in reduction of both oxygen impurities and hydrogen recycling in plasma. However, there are a few issues for reducing of hydrogen included in boron film and for stabilizing of DC glow discharge cleaning (GDC) during the boronization. To solve the issues, a new boronization method using deuterated-decaborane (B₁₀D₁₄) was adopted instead of the conventional B₁₀H₁₄. As a result, hydrogen content in the boron film decreased clearly, and the discharge conditioning shots for decreasing hydrogen concentration in plasmas after the boronization was reduced to 1/10 in comparison to the conventional process. Furthermore, GDC became stable, with only helium dilution gas, and it was possible to save 30 hours in maximum of the time necessary for boronization. It was found that the boronization using B₁₀D₁₄ is very efficient and effective method for the first wall conditioning.