Designs and technologies for plasma-facing wall protection in EU DEMO

The EU DEMO plasma is almost completely enveloped by large breeding blanket segments for tritium breeding and power extraction. Shaping of the blanket plasma-facing wall in 3D may prove to be essential, but this strategy alone is not sufficient to protect against anticipated transient plasma events. The high heat flux wall-limiter approach used in ITER is not thought to be viable in a tritium self-sufficient power reactor, and so in EU DEMO wall protection using discrete limiters is pursued. Two types of discrete limiter are described in this paper. One is an equatorial port limiter designed to handle the power during the plasma start-up phase, making use of water-cooled tungsten/CuCrZr monoblock technology. The second is the upper limiter, featuring a plasma-facing component designed specifically for extreme transient loading due to a vertical displacement event. The heat flux channelling and thermal barrier features of this design are shown to considerably reduce CuCrZr pipe temperature, and so reduce the likelihood of catastrophic failure. A preliminary neutronic calculation has shown that the impact of these discrete limiters on overall tritium breeding ratio is relatively low.