Design and engineering of the Alcator C-Mod lower hybrid current drive system

The PSFC group of MIT and PPPL are jointly developing a Lower Hybrid Current Drive (LHCD) system for installation on the Alcator C-Mod tokamak, with the primary goal of driving plasma current. Twelve Klystrons will feed a coupler with an input power of 3 MW at 4.6 GHz and a pulse length of 5 seconds. The coupler is composed of 4 arrays, each with 24 wave-guides (96 total) which are stacked poloidally and are symmetric about both the vertical and horizontal planes. The four-stacked arrays are installed through a single equatorial port and can be axially adjusted to provide optimum plasma coupling. Material selections and spatial limitations required innovative design solutions that will be described.