First demonstration of a traveling wave antenna in a tokamak and relevance to the JFT‐2M combline

First observations of a traveling wave antenna (TWA) in a tokamak are reported. For a fractional bandwidth (δω/ω) of about 20%, TWA experiments using a four‐element antenna in DIII–D showed less than 1% reflected power and excellent stability of the phase velocity of the launched wave—even during giant ELMs. The power radiated into the plasma varied from about 40% during ELM‐free H‐mode to almost 90% during L‐mode and ELMing H‐mode. Theoretical modeling validated by these low power observations is used to predict the plasma load resistance of a high power combline being built for JFT‐2M.