Progress of DTT ECH System Design

The Divertor Tokamak Test (DTT) facility [1], whose construction is starting, will study a suitable solution for the power exhaust in conditions relevant for DEMO. The tokamak will reach the needed condition of 15 MW/m power flow outwards through the separatrix by coupling up to 45 MW of auxiliary heating power to the plasma. To achieve this goal, the selected heating systems are Electron Cyclotron Heating (ECH), Ion Cyclotron Heating (ICH) and Negative Neutral Beam Injector (NNBI). The EC system relies on up to 36 gyrotrons: 170 GHz, 1-1.2 MW and 100 s of pulse length. For the power transmission, a Quasi Optical (QO) approach has been chosen, consisting of multi-beam mirrors installed under vacuum to reduce the overall transmission losses below the target of 10%. The power will be injected into the tokamak using independent (single-beam) front-steering mirrors capable to steer all the beams in real-time for assisted plasma breakdown, NTM and ST control, ECCD and main electron heating. Although the ECH system design presented here will be based mainly on existing and assessed technologies, like the 170 GHz gyrotron type developed for ITER and the QO line installed at W7- X, challenging adaptations to the DTT case are designed. In particular, the design of a QO multibeam line under vacuum is novel and needs detailed analysis of the stray radiation along the line in order to set the requirements for the mirror dimensions and/or the cooling of the vacuum chamber that encloses the mirrors. A further relevant question is the reliability of the EC system; the development of automatic algorithms to control such a large number of gyrotrons is foreseen to provide the required amount and distribution of power into the plasma.