Design of DIII-D Advanced Divertor

The Advanced Divertor is a modification being designed for the plasma chamber of the DIII-D tokamak in order to optimize the divertor configuration and allow a broader range of experiments to be carried out. The design of the Advanced Divertor is described. It will enable two classes of physics experiments to be run in the DIII-D: divertor biasing and divertor baffling. The Advanced Divertor's two principal components are a toroidally symmetric baffle and a continuous ring electrode. The tokamak can be run in baffle, bias, or standard DIII-D divertor modes by accurately positioning the outer divertor strike point with the DIII-D plasma control system. The baffle will provide approximately 50000 L/s pumping for particle removal in the outer bottom corner of the vacuum vessel. The strike point will be positioned at the entrance aperture for the baffle mode. The aperture geometry is designed to facilitate a large particle influx plus a high probability that backstreaming particles will be reionized and redirected to the aperture. Where the baffling plates meet, gas sealing is required to prevent recycling of neutrals back into the plasma. The supports for the ring are radially flexible to handle the differential thermal growth between the ring and the vessel wall, but are stiff in the vertical direction to restrain the ring against large disruption forces. Tests of insulators, performed in the DIII-D during plasma operations prior to deciding on the final design, and other testing and analyses performed to evaluate insulating materials and concepts are described. >