HEATING AND CONFINEMENT CHARACTERISTICS OF 2ND HARMONIC 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 2-omega-cH) scheme and the hydrogen minority second harmonic (H-minority 2-omega-cH) scheme (n(H)/n(He) almost-equal-to 0.1) in two toroidal phasing modes of antenna currents, in phase ((0, 0)) and out of phase ((pi, 0)), at P(IC) less-than-or-equal-to 3 MW, nBAR(e) = (1.3-6.6) x 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, tau-E(inc), for (pi, 0) phasing is larger than for (0, 0) phasing, irrespective of the heating scheme. In particular, H-minority 2-omega-cH heating with (pi, 0) phasing shows excellent plasma heating with tau-E(inc) almost-equal-to 100-120 ms, which is larger than that of neutral beam injection (NBI) heating by a factor of about two. Different dependences of tau-E(inc) on I(p) are obtained in the two heating schemes. The (0, 0) phasing data of tau-E(inc) in H-majority 2-omega-cH heating increase with I(p) up to 1.9 MA, while the (pi, 0) phasing data in H-minority 2-omega-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 2-omega-cH heating at high density agrees well with the Shimomura-Odajima scaling.