Overview of the Divertor Tokamak Test Facility project

One of the main challenges, within the European Fusion Roadmap, in view of the construction of a demonstration plant (DEMO, the first nuclear fusion power plant able to provide power to the electricity grid around 2050), is the thermal power on the divertor. ITER plans to test the actual possibilities of a "standard" divertor operating in a plasma fully detached condition, i.e. no contact between plasma and first wall of the vessel. This solution could be unsuitable to be extrapolated to the operating conditions of DEMO and future reactors; then the problem of thermal loads on the divertor may remain particularly critical in the road to the realization of the reactor. For this reason, a specific project has been launched, aimed to define and design a Tokamak named "DTT (Divertor Tokamak Test)". This Tokamak has to carry out a number of scaled experiments, to be integrated with the specific physical condition expected and technological solutions included in DEMO. DTT should retain the possibility of testing different divertor magnetic configurations, including liquid metal divertor targets, and other possible solutions promising to face with the power exhaust problem. The construction has recently been approved by the Italian government. DTT will be a high field superconducting toroidal device (6 T) carrying plasma current up to 5.5 MA in pulses with length up to about 100 s and with 45 MW of additional heating power. The nominal cross section is elongated with a major radius R=2.11 m and a minor radius a=0.64m. The DTT parameters are selected so as to reproduce edge conditions as close as possible to those expected in DEMO (in terms of a set of dimensionless parameters characterizing the physics of Scrape Off Layer, SOL, and of the divertor region), while fully fitting (again, in terms of the dimensionless parameters) with DEMO bulk plasma performance. Maximum flexibility is guaranteed, within the limits of a given budget and a tight time schedule consistent with the needs of the European Road Map. This paper describes the status of the design activities of DTT. Emphasis is given on an integrated design approach, illustrate the rationale for the design choices, focusing on the main components, namely magnet system, plasma scenarios, vacuum vessel, in-vessel components, thermal shield, neutron shield, and additional heating system.