The new divertor tokamak test facility

Appropriate disposal of the non-neutronic energy and particle exhaust in a reactor is universally recognized as one of the high priority challenges for the exploitation of fusion as an energy source. The new Divertor Tokamak Test (DTT) facility, which will be built in Italy, is a tool to address that challenge in high-field, high performance tokamak with complete integration between core and edge plasma scenarios. Background. The controlled exhaust of energy and particle from a fusion reactor is a difficult issue that has to be solved before starting the design of DEMO. According to experimental and theoretical work (see for example [1]) one of the major risks comes from the size of the scrape off layer (SOL) power flow decay length lq, which - from data taken in existing experiments - scales as [2]: ?" (mm) = 1,35 P-./01.13 R1.15B701.85e1.53 (1) where PSOL is the power in the scrape-off-layer, R the major radius of the machine, Bp the poloidal magnetic field and e the inverse aspect ratio. Activity is ongoing to fully assess both theoretically and experimentally the behaviour of lq, taking into account the role of turbulence and of the main plasma parameters (see for example [3]) If this scaling holds true for ITER, it means that in that device lq is expected to be of the order of 1 mm. Considering the Q=10 scenario, with 500 MW of net fusion power (400 MW brought by neutrons and 100 MW heating the plasma and lost through radiation and thermal/particles losses) the expected power exhausted on the divertor in a low radiation case is about 90 MW. This means a heat flux on the divertor of the order of 50 MWm-2, a value far above the limit of present target materials. To cope with these challenges and following the recommendations of the EUROfusion roadmap [4], the Italian fusion community proposed in 2015 the DTT experiment.