Transmission Line Technology for Electron Cyclotron Heating

We briefly review the history of transmission line technology for electron cyclotron heating (ECH) applications and then survey the major developments over the past few years. These developments are grouped by function. Papers in this special issue are highlighted. We concentrate on the transmission from a matching optics unit near a gyrotron microwave source to the location of a vacuum window near the plasma, without review of window and launcher technology. Prospects for components handling more than 1-MW continuous wave are reviewed. While both waveguide and free-space propagation are considered, a greater emphasis is placed on corrugated waveguide components in preparation for the ITER ECH system.