Design of DIII-D armor tiles

An upgrade of the vessel protection system for DIII-D is in progress. The ceiling, floor, and inner wall are being armored to enable operation of double null diverted plasmas and to enable the use of the inner wall as a limiting surface. The present armor configuration is partial coverage of the vessel wall with a combination of Inconel X-750 tiles and Inconel tiles with 1 cm graphite caps brazed to the plasma facing surface. The graphite is located only in the areas of neutral beam shinethrough and divertor targets on the floor. The existing brazed design has had limited success at the present operational energy levels which are below the capability of the machine. The new armor tile design utilizes the existing mounting studs and stud pattern in the vessel and is compatible with existing and planned diagnostics. The 10 minute duration between pulses requires the tiles to be conductively cooled by the vessel wall. Using two and three-dimensional analyses, the file design is optimized for thermal loading. Minimizing the stresses around the hold-down and eliminating stress concentrators is also emphasized in the design. The tiles are made from graphite, and a process to select a particular grade of graphite was developed. Thermal shock parameters have been compared, and testing of the graphites for thermal shock in an ion beam test facility has been carried out. The design of the tile fastener system incorporates the hold-down forces required for thermal conductance to the vessel and for holding the tile against eddy current forces. Special graphite materials are being used for tiles which have instrumentation mounted in them. A carbon-carbon composite with random fiber reinforcement was chosen for special tiles. 4 refs., 4 figs