Heating and confinement characteristics of second hearmonic heating in the ion cyclotron range of frequencies on the JT-60 tokamak

Results are presented of the second harmonic heating experiments in the ion cyclotron range of frequencies (ICRF) on JT-60. Heating and confinement characteristics are investigated by using the hydrogen second harmonic (H-majority 2ω cH scheme and the hydrogen minority second harmonic (H-minority 2ω cH scheme (n H /n He ≈0.1) in two toroidal phasing modes of antenna currents, in phase ((0,0)) and out of phase ((π, 0)), at P IC ≤ 3 MW, n e =(1.3−6.6) × 10 19 m −3 and I p = 1–2.4 MA. Efficient plasma heating has been demonstrated in both heating schemes. Intense non-Maxwellian ion tails are observed at low density. Sawtooth oscillations with an enhanced period in the electron temperature are found over a wide range of electron densities. The incremental energy confinement time, τ E inc , for (π, 0) phasing is larger than for (0,0) phasing, irrespective of the heating scheme. In particular, H-minority 2ω cH heating with (π, 0) phasing shows excellent plasma heating with τ E inc ≈ 100–120 ms, which is larger than that of neutral beam injection (NBI) heating by a factor of about two. Different dependences of τ E inc on I p are obtained in the two heating schemes. The (0,0) phasing data of τ E inc in H-majority 2ω cH heating increase with I p up to 1.9 MA, while the (π, 0) phasing data in H-minority 2ω cH heating are almost constant with I p up to 2.4 MA. The global energy confinement shows an L-mode behaviour. The energy confinement time for H-minority 2ω cH heating at high density agrees well with the Shimomura-Odajima scaling.