Heating and current drive by electron cyclotron waves in JT-60U

The results of studies on heating and current drive by the electron cyclotron (EC) waves in JT-60U are presented. An electron temperature of up to 26 keV, as measured by ECE diagnostics, was achieved by injecting EC waves into the centre of a reversed shear plasma produced by the lower hybrid (LH) waves. The electron temperature Te exceeds 24 keV in the region ρ < 0.3, where ρ is the normalized minor radius. The EC driven current profile was measured at high Te up to 21 keV without using LH waves, and was found to be spatially localized. The ECCD (current drive) efficiency ηCD increased with Te and reached 0.42 × 1019 A W−1 m−2 at Te = 21 keV. The dependence of normalized CD efficiency on deposition location was also studied to optimize the CD efficiency, since the trapped particle effect, which depends strongly on deposition location, is expected to reduce ζ. The effect was detected from a significant decrease in ζ in the lower magnetic field deposition, which is consistent with a linearized Fokker–Planck calculation. The measured CD efficiency ζ increased with electron density ne for the same Te, which showed a stronger dependence on ne compared with the linear calculation. Further off-axis ECCD profile at about half of the minor radius was measured, showing fairly good agreement with linear calculation.