Lower hybrid current drive and higher harmonic ICRF heating experiments on JT-60

The paper describes the latest results and analysis of LHCD and ICRF heating experiments and beam induced instabilities on JT-60. A new multijunction LHCD launcher recorded current drive efficiency η_CD (≡n̄_eR_pI_RF/P_LH) of 3.4 × 10¹⁹ m^-2·A·W^-1 and extended current drive products (≡n̄_eR_pI_RF) up to 12.5 × 10¹⁹ m^-2·MA with approximately 4.5 MW LHCD power. Combination with neutral beams showed that the interaction between ions or electrons and lower hybrid waves is well explained by simple lower hybrid dispersion and showed evidence of N_∥ upshift. A simplified N_∥ upshift model explains experimental η_CD very well and predicts the achievement of the value necessary for ITER. Experimental results on third harmonic ICRF heating in combination with NBI heating and second harmonic minority heating are presented. In both cases, strong central heating by tail ion acceleration with higher harmonic ICRF waves occurs and giant sawteeth appear. In the former case, the sawtooth period reaches six times the energy confinement time and the energy confinement time is enhanced by 20% owing to fast ions. In the latter case, giant sawteeth appear even in the high density and low q regime (n̄_e ≤ 6.5 × 10¹⁹ m^-3 and q_eff ≥ 2.6) with relatively small threshold ICRF power (approximately 2 MW).