Enhanced current drive efficiency in a long discharge on TRIAM-1M

The enhanced current drive (ECD) efficiency mode, which is characterized by a spontaneous increase of current drive efficiency ηCD from (0.3-0.4) × 1019A/W m-2 to (0.6-1.0) × 1019 A/W m-2, is observed in long pure LHCD plasmas on TRIAM-1M. The energy confinement time is also improved due to the increase of line averaged electron density, and of the ion and electron temperatures. The current drive efficiency is proportional to the electron density. The transition to ECD mode occurs at a critical density, which depends slightly on the refractive index in the toroidal direction N|| of the injected wave.