RF Systems Development on DIII-D

The DIII-D RF Systems include an Electron Cyclotron Heating and Current Drive system (ECH/ECCD) System, a Helicon System, and a high field side Lower Hybrid Current Drive (LHCD) system. The ECH system is expected to add three more 110 GHz gyrotrons in 2022, and a 3rd top launcher is funded. The ECH waveguide upgrade to larger size for enhanced transmission in the ECH lines is studied.

The 1 MW 476 MHz Helicon system at DIII-D aims to demonstrate off-axis current drive of up to 60 kA in plasmas. The initial tests demonstrated up to 300 kW coupled power with core electron heating observed, and the aim to double the coupled power this year.

The LHCD System will include in the first step up to 1 MW of generated power from 4 klystrons injected on the high field side of the DIII-D vessel. The coupler for the LHCD System at 4.6 GHz was designed to maximize coupled power, and additive manufactured (AM) of GRCop-84 enabled integrated matching into each of the aperture joints. Upgraded AM approaches are investigated for larger components to reduce the post AM processes. We seek to assess the viability of traveling wave couplers for increased efficiency as an upgrade for the present finite directivity couplers. The LHCD installed power will be increased from 1 to 2 MW.