Fusion power: breeder blankets and diverter technologies put to the test

Currently, the engineering research towards DEMO is mainly directed towards two particular subsystems of importance to the electricity-generating fusion reactor: the diverter, where the fusion plasma comes into contact with the vessel, and the blanket, which generates tritium for the fusion fuel and houses the cooling circuits.

Three diverter technologies are currently under consideration. These are known as snowflake, liquid-metal and SUPER-X exhaust.

Both snowflake and SUPER-X exhaust spread the impact of the plasma over a wider area than that of the diverters used in tokamaks like JET and WEST, which formed the basis of the design that is being manufactured for ITER. Magnets called correction coils, around the base of the reactor vessel, shape the plasma so that it contacts both edges of a trench-shaped component. The energy load is huge: more than 10 MW per square metre, higher than a spacecraft re-entering Earth’s atmosphere.

In the snowflake diverter, a different arrangement of correction coils shape the plasma into a snowflake-like shape, which contacts a wider diverter at several points, each of which will therefore experience less thermal load than the trench-shape diverter. This, explained Eurofusion’s Tony Donné, will reduce wear on the diverter sections, and increase their lifetime, while also reducing the risk of particles scraped off the diverter contaminating the plasma. As each diverter segment is made out of large, solid forgings of tungsten, this will reduce the running costs of the reactor and also make maintenance more simple.