The Cascading Pebble Divertor for the Spherical Tokamak Power Plant

The Cascading Pebble Divertor for the Spherical Tokamak Power Plant

The Cascading Pebble Divertor for the Spherical Tokamak Power Plant 150 150 Mathew

The Cascading Pebble Divertor for the Spherical Tokamak Power Plant

The design of a power plant based on the spherical tokamak (ST) is being developed in order to explore its potential advantages. The plasma is operated in a double null configuration, forming both an upper and lower divertor. In order to accommodate the high erosion rates and heat fluxes developed in the divertors, a system based on a cascading flow of silicon carbide pebbles is being developed. The pebbles flow into the upper divertor where they fall as a toroidal curtain, which intercepts the divertor particle flux. The pebbles then flow under gravity through ducts to the lower divertor where they form a similar curtain. The bulk temperature of the pebbles rises to about 1200°C although the outer surface is transiently heated to about 1800°C. The pebbles pass out of the vacuum chamber into holding tanks and then into a fluidised bed heat exchanger. Here the pebbles are cooled down to about 300°C and dust and damaged pebbles are removed. The pebbles are transferred to an upper tank by a pneumatic conveyor where the remaining gas is removed and the pebbles flow into the upper divertor again.

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01/01/2005