PROPERTIES OF BORON COATINGS USED AS PLASMA-FACING MATERIAL OF FUSION DEVICE

For the boron films made by a d.c. glow discharge for a gas mixture of diborane and helium, numerous surface properties were intestigated and the characteristics of the boron film as a plasma facing material in fusion devices were evaluated. The ability of the boron film to getter the oxygen was estimated as about 10(21) O atoms m(-2). The gettered oxygen in the boron film was observed in the surface to a depth of less than about 30 nm. The hydrogen concentration of the baron film made at room temperature was approximately 30%. The hydrogen in the film desorbed at about 573 K. This desorption temperature was considerably lower than that of graphite. These results directly indicate that the boron film coated on the graphite wall can largely reduce the particle recycling, in addition to the reduction in the oxygen impurity level in the plasma. After the oxygen gettering, the oxygen existed in the form of B-O bonds. It is also noted that the boron film absorbed both the oxygen and the carbon after exposure to the atmosphere.