Status of DTT ECH Transmission Lines and Antennae

The divertor tokamak test (DTT) facility is designed to study the power exhaust methods in scenarios similar to those expected in future fusion plants like DEMO. The project foresees 45 MW of external additional heating power to the plasma, provided by electron cyclotron heating (ECH), ion cyclotron heating, and neutral beam injector. This article focuses on the present status of the design of the transmission lines (TLs) and antennas for the ECH system. In the first operational phase, the system shall include 16 gyrotrons (1 MW/170 GHz/100 s), grouped into two clusters of eight sources each. In a later stage, the total installed power shall be doubled for a total of four clusters. Quasi-optical TLs connect the EC sources, located in a dedicated building, to the tokamak, via mirrors transmitting the microwave beams inside vacuum pipes to reduce losses and risks of arcing in air. Each TL consists of three main sections: two single-beam (SB) sections with small mirrors dedicated to a single beam at the beginning and the end of the line and a midsection of multibeam (MB) mirrors for the transmission of all the eight beams of the cluster. The beams at the output of the TL match the antennas installed in the equatorial and upper ports of the same vacuum vessel sector, through corrugated circular waveguides (WGs). The WGs are needed to reduce the vacuum conductance between the DTT vessel and TLs environments, being the connection with the vacuum vessel managed by all-metal gate valves without diamond windows. The two antennas consist of independent launching modules for each beam composed by two mirrors, one fixed and one steerable. All the components of the system are actively water-cooled to limit deformations of the mirrors surface to ensure the required quality of the beams and to reduce the transmission losses.