Effects of Nonlinear Wave Absorption on the Radiation Loss Fraction during Second Harmonic Minority Ion Cyclotron Resonance Heating Experiments in JT-60U

The ratio of an increment in radiation power to ion cyclotron resonance heating (ICRH) power (ΔP rad main/P IC) decreased from about 40% to below 10% with increasing ICRH power in JT-60U. The most plausible mechanism for the anomalous behavior of ΔP rad main/P IC is inferred to be nonlinear wave absorption, which was experimentally estimated from the time derivative of the diamagnetic stored energy at the turn-off timing of the ICRH pulse. Nonlinear wave absorption observed during the experiments supported the theoretical estimation using a full wave code incorporating the 1-D Fokker-Planck code.