Critical design issues in DEMO and solution strategies

The EU fusion roadmap defines as a goal the development of a DEMO, which achieves a long plasma operation time and demonstrates tritium self-sufficiency and net electricity output. Eight design issues have been identified as critical: (i) feasibility of wall protection limiters during plasma transients, (ii) integrated design of breeding blanket and ancillary systems, (iii) power exhaust taking advantage of advanced divertor configurations, (iv) tokamak architecture based on vertical blanket segments, (v) direct or indirect power conversion concept, (vi) configuration of plant systems in the tokamak building, (vii) feasibility of hydrogen separation in the torus vacuum pump and direct recirculation, and (viii) plasma scenario. For each of these issues potential solutions have been identified and activity plans have been defined for the associated developments and assessments. Two of these affect in particular the integrated design of the DEMO machine, namely (i) and (iv). These are introduced and discussed in this article providing a summary of identified risks, requirements, and solution concepts. For the remaining six design issues references are provided only due to space limitations in this article.