Current drive and confinement studies during LHRF experiments on JT-60

TLDR

The divertor effectively removes impurities from fast electrons, enabling reactor‑grade RF current generation in low‑density plasma. First LHCD experiments in JT‑60 produced 2 MA RF‑driven current, achieving efficiencies ηCD = 0.8–1.7 (10^19 m^−3 A W^−1); NBI heating boosts efficiency by 1.5× and LHCD improves confinement, with active current‑profile control identified as key to confinement improvement.

Abstract

Results are presented of the first Lower Hybrid Current Drive (LHCD) experiments in JT-60. 2 MA of RF driven current is successfully produced for the first time in a reactor grade tokamak. The magnetic divertor works quite well in eliminating the impurities released by the current carrying fast electrons which have allowed the generation of the reactor relevant RF current in a very low density plasma. The efficiency which is defined as ηCD = eRIRF/PLH(1019 m−3 A·W−1), reaches values of 0.8 to 1.7. NBI heating enhances the current drive efficiency by a factor of 1.5, and LHCD improves the confinement time of high power NBI heated plasma. The key to confinement improvement is found to be the active control of the current profile by LHCD.