Reduction of carbon influx by minimizing tile heating in DIII-D

As predicted by theoretical models, under certain plasma configurations the edges of the graphite tiles lining the walls of the DIII-D vacuum vessel can exceed 2000°C. This is the temperature at which ablation occurs for the ATJ graphite material for localized heating (1500°C for the face of the tile) and thus represents an operational limit for the tokamak. This theoretical prediction is confirmed by observed increased carbon contamination in the plasma and wearing of the tile edges. Several approaches were investigated to minimize tile edge heating by reducing the amount of heat flux on the tiles toroidal and poloidal surfaces. This was accomplished by modifying the geometry of the top two rows of the DIII-D centerpost tiles