DIII-D Electron Cyclotron Heating and Current Drive System Status and Plans

The DIII-D 110-GHz electron cyclotron heating and current drive (ECH/ECCD) system supports a wide range of experiments at the DIII-D National Fusion Facility and is pioneering innovative new techniques for future fusion reactors. The system currently includes eight sockets with four installed gyrotrons, 31.75-mm circular corrugated transmission lines, and four dual real-time steerable launchers plus two top launchers (TLs). After the successful testing of the first TL, this injects the EC waves downward nearly parallel to the resonance layer with double current drive efficiency and a long absorption path, and a second new TL was designed and installed with an upgraded design. Some of the operational limitations encountered for the 110-GHz X-mode second harmonic resonance scenario launched in overdense plasmas were overcome with the alternative use of O-mode second harmonic launch. Two new gyrotrons in a new series manufactured by Communications and Power Industries (CPI) were installed and tested, bringing up the total installed power to 3 MW. The installation of repaired and new gyrotrons will increase the number of installed gyrotrons to 7 in 2023. An addition to the DIII-D building will be completed in early 2022 to provide the space to expand the ECH/ECCD system to ten gyrotron systems plus an extra gyrotron test socket.