The DTT proposal. A tokamak facility to address exhaust challenges for DEMO: Introduction and executive summary

As indicated in the European Fusion Roadmap, the main objective of the Divertor Tokamak Test facility (DTT) is to explore alternative power exhaust solutions for DEMO so as to mitigate the risk that the conventional divertor based on detached conditions to be tested on the ITER device cannot be extrapolated to a fusion reactor. The issues to be investigated by DTT include: demonstrate a heat exhaust system capable of withstanding the large load of DEMO in case of inadequate radiated power fraction; close the gaps in the exhaust area that cannot be addressed by present devices; demonstrate that the possible (alternative or complementary) solutions (e.g., advanced divertor configurations or liquid metals) can be integrated in a DEMO device. In this paper, we describe a proposal for such a DTT, presented by ENEA in collaboration with a European team of scientists. The selection of the DTT parameters (a major radius of 2.15 m, an aspect ratio of about 3, an elongation of 1.6-1.8, a toroidal field of 6T, and a flat top of about 100s) has been made according to the following specifications: edge conditions as close as possible to DEMO in terms of dimensionless parameters; flexibility to test a wide set of divertor concepts and techniques; compatibility with bulk plasma performance. an upper bound of 500 M for the investment costs. This paper illustrates this DTT proposal showing how the basic machine parameters and concept have been selected so as to make a significant step toward the accomplishment of the power exhaust mission.