Lower hybrid current drive efficiency in the JT-60 tokamak

Lower hybrid current drive (LHCD) experiments on JT-60 have been carried out in parameter ; e = (0.6−1.6) × 10 19 m −3 , I p = 0.5−1.5 MA, B T = 2.7−4.5 T, P LH < 2.5 MW, f = 1.75 and 2.0 GHz, with and without NB heating (P NB < 6 MW), limiter and lower side single null divertor configurations, and narrow and wide spectra. The current drive efficiency increases with the volume averaged electron temperature ⟨T e ⟩ and with decreasing Z eff and a high efficiency of η CD ≡ e R P I RF /P LH ≤ 2.65 × 10 19 m −2 ·A·W −1 was achieved by LHCD alone. The experimental data set has shown that the current drive efficiency is consistent with the scaling of η CD ∼ 12 ⟨T e ⟩/(5+Z eff ) × l0 19 m −2 ·A·W −1 . Low N 1 waves with a narrow spectrum have a higher current drive efficiency than higher N 1 waves with a wide spectrum insofar as launched waves satisfy the accessibility