Development of RF based capacitively coupled plasma system for tungsten nano layer deposition on graphite

Based on the advancement in current thermonuclear fusion research, it is quite likely that future generation fusion machines, DEMO and beyond, will be operating with tungsten and alloys based on tungsten as the plasma facing material on their walls and targets to dissipate the thermal as well as particle loads under extreme operational conditions. Tungsten is being preferred because of its superior thermo-mechanical properties, chemical resistance as well as for its low tritium retention capabilities. However, use of pure tungsten as a structural material itself will substantially increase the manufacturing cost and overall system mass and also it is difficult to machine tungsten in to desired shapes. Hence, tungsten coatings on lighter substrates such as graphite are preferred which essentially reduce the cost and structural weight of the target materials considerably. In this article, we report the development of a RF based capacitively coupled plasma reactor for tungsten coating on graphite tiles using plasma assisted chemical vapour deposition at SVITS, India. Tungsten nano layers have been successfully deposited on graphite test pieces by plasma assisted reduction of the heavy tungsten hexafluoride gas in hydrogen. Characterization and post analysis of the tungsten coated tiles has been carried out to study the presence of tungsten, thickness of the coating, thermal fatigue etc.