Properties of thick coatings of carbon and carbon-boron prepared by vacuum ARC deposition

Abstract

Carbon coatings on the first wall and the shielding of the first wall by graphite tiles effectively improve plasma parameters by reducing radiation losses in the plasma. In this experiment, a fast in-situ coating method of low atomic number materials by a compact vacuum-arc deposition gun was developed. This method is useful for in-situ carbon coating on the first wall as well as for in-situ regeneration of coatings on graphite tiles damaged through plasma wall interactions or by high heat loads from the plasma. Thick carbon and carbon-carbon coatings of up to the thickness of 310 μ im were made on molybdenum or tungsten by this deposition gun. The deposition rate of carbon coatings depended on the ambient gas. In an argon environment, the deposition rate ws 3 μ g/min and in a hydrogen environment, it was 1 μ g/min; the distance between the evaporator and the substrate was 40 mm. X-ray diffraction analysis indicates that the degree of disorder jn the crystal structure of the coating films deposited in argon is larger than that deposited in hydrogen. Many diffraction peaks associated with Mo 2 C, WC and W 2 C were observed in the X-ray diffraction. These peaks show that the interdiffusion between the deposited film and the substrate increased the adhesive strength of the deposited film to the substrate.