High coupling performance of JT-60U ICRF antennas

Sufficient coupling of an ICRF antenna for high power experiments was obtained even for a wide gap between the separatrix and the antenna in JT-60U. The loading resistances for an out-of-phase mode are over 4 Omega for a gap of 13 cm between the separatrix and the Faraday shield over the wide range of electron density from 1 × 10 19 to 5.5 × 10 19 m -3 . In particular, the loading resistances for an in-phase mode are about 5 Ω for a gap of 33 cm between the separatrix and the Faraday shield for the same plasma parameters. However, the heating response for the out-of-phase mode is much stronger than that for the in-phase mode