Boronization using deuterated-decaborane in JT-60U

Abstract

In JT-60U, boronization using hydride-decaborane (B/sub 10/H/sub 14/) 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 (B/sub 10/D/sub 14/) was adopted instead of the conventional B/sub 10/H/sub 14/. 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 B/sub 10/D/sub 14/ is very efficient and effective method for the first wall conditioning.