Third-harmonic electron cyclotron heating for tokamak high-beta profile control studies

Third‐harmonic extraordinary‐mode ECH could be employed for D III‐D high‐beta studies at reduced toroidal magnetic field. D III‐D neutral beam injection increases the electron temperature above 4 keV. At 4×1019 m−3 density, the third‐harmonic 120 GHz ECH power should be absorbed with greater than 80% efficiency. Absorption would increase at higher temperature unless the distribution function is too severely distorted by the high‐power ECH. A 6 MW‐120 GHz system could thereby allow well‐controlled beta and profile control studies using third‐harmonic ECH.