The folded waveguide: a high frequency rf launcher☆

Abstract The folded waveguide, an alternative to loop antennas for launching power in the ion cyclotron range of frequencies (ICRF) into plasma devices, operates as a cavity with apertures for coupling RF power to the plasma. The RF field pattern is similar to that of a loop antenna, but with a lower ratio of electric to magnetic field. Power enters from a coaxial line via a sliding contact, whose position matches impedances between the coaxial line and the folded waveguide. The folded waveguide has operated at 1 MW and promises high power density. Calculations indicate a factor of 4 increase in power handling capability over a comparable loop antenna. The possible use of the folded waveguide on several tokamaks is discussed.