Formation of high electron temperature plasmas in ECH experiments on JT-60U tokamak

摘要

Formations of high electron temperature plasmas with ECH/ECCD were studied on the weak and/or reversed shear (R/S) plasmas. EC wave was injected with an oblique toroidal angle for Co-ECCD. A strongly peaked electron temperature profile with T_(e0) more than ～15 keV was observed on the ECE polycrometer in the case of on-axis EC injection just after the plasma current ramp-up. The MSE measurements showed that a strong R/S configuration was produced in the central region during ECH/ECCD. The foot in the steep Te profile corresponded to the q_(min). The maximum electron temperature was limited by a thermal collapse at the central hot region within r/a～0.15. In a preliminary study, the central hot region was slightly expanded by broadening the EC deposition. Meanwhile effective heating was observed on the strong R/S plasmas with the internal transport barrier (ITB), which were already produced by LHCD and/or NB injection during Ip ramp-up. The whole electron temperature inside the ITB increases during ECH/ECCD. An enhancement of the R/S configuration was observed during on-axis ECH/ECCD even though a large central EC driven current was expected by the Fokker Planck prediction. In the LHCD R/S plasma at low density (n_e ～ 0.4x10~(19) m~(-3)), the central electron temperature increased up to Teo ～ 26 keV with keeping the ITB at r/a～0.4. Repeated collapses, which weakened the R/S configuration, were observed during high T_e plasma formation. These ECH/ECCD results indicate the strong correlation of current profile with the formation of high T_e plasma.