Conceptual design of CFETR electron cyclotron wave system

•The conceptual design of 170 GHz/20 MW electron cyclotron wave system was introduced.•The layout of RF sources was given.•The design and layout of transmission lines were shown and series of microwave components were introduced.•The structure of launcher was described in detail.•By the optic calculation and optimization of RF propagation inside the launcher, the quasi-optical parameters for launcher design were given. And then temperature distribution and thermal-stress of the injection mirror were analyzed.

China Fusion Engineering Test Reactor (CFETR) is a test tokamak which is built for magnetically confined fusion plasma experiments. The electron cyclotron (EC) wave system of CFETR is designed to inject 20 MW RF power into the plasma for heating and current drive (H&CD) applications. The EC wave system consists of RF sources, twenty transmission lines (TLs) and one equatorial launcher. RF sources contain twenty gyrotrons with the output power 1 MW. There are series of microwave components distributed along the TL and the percentage of power losses of each TL is about 8.7%. In the equatorial launcher, five RF beams are injected into one focusing mirror and then reflected to the plasma via one injection mirror. The focusing mirror is spherical to focus Gaussian beam and the injection mirror which is flat can steer in the toroidal direction. After optic calculation and optimization, all the quasi-optical parameters for launcher design are given. Combining with the thermal stress analysis, the chosen inner diameter of water channel of injection mirror is 12 mm and the suggested water velocity is 3 m/s.