Fabrication of tungsten coated graphite tiles for Aditya Upgrade Tokamak

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. Usage of pure tungsten is not possible because it will substantially increase the manufacturing cost and overall system mass. It is also 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 paper, we report the production of tungsten coated graphite tiles for ADITYA-U tokamak and their characterization. Tungsten nano layers have been successfully deposited on limiter tiles of ADITYA-U made up of graphite by plasma assisted reduction of the heavy tungsten hexafluoride gas in hydrogen. Coating thickness of ~ 1 micron has been achieved. Although the uniformity of the coating still needs to be improved the bonding of tungsten on the surface of the graphite tiles seems to quite good. The tiles are made available for insertion into ADITYA-U machine and pre and post exposure analysis of the coated surface will be carried out soon. Details on optimization of plasma parameters for successful coating and characterization and post analysis of the tungsten coated tiles to study the presence of tungsten, thickness of the coating, thermal fatigue etc. will be presented in this paper. (author)