Overview of electron cyclotron heating and electron cyclotron current drive launcher development in magnetic fusion devices

In any system designed for electron cyclotron (EC) heating (ECH) and EC current drive in fusion plasmas, the launcher is the matching element between the plasma and the transmission line. Only an appropriate launcher achieves efficient use of the gyrotron power for the many different high-power EC H&CD applications. The frontier is now set at approximate to 4 MW of launched power at 110 to 140 GHz for approximate to 10 s, to be further moved to approximate to 10 MW, 1000 s in the near future. ITER will push the limit to 20 MW, 170 GHz. The workhorse of the antenna system is the front steering setup consisting of a movable mirror, or a mirror array, in front of the hot plasma, which provides for full flexibility in the EC H&CD applications. However, because of the concern associated with cooled and movable parts in a hostile environment, air arrangement with movable mirrors positioned far from the vessel port, and connected to the plasma by imaging waveguides, is being developed as a remote steering backup solution. In a reactor, where flexibility is much less relevant than reliability, the situation could reverse. Techniques for a radial scan of the deposition layer different from front beam steering are discussed in this paper. The ideal goal would be a 100% coupling of the launched EC power, to occur within approximate to 2% of the plasma size and through pipes of size negligible with respect to the vessel, without negative impact on plasma periphery in spite of the high power densities transmitted through the edge.