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Report No.

Turbulence analyses of improved electron energy confinement in H-mode plasmas with gyrokinetic calculations

Narita, Emi; Honda, Mitsuru; Hayashi, Nobuhiko; Takizuka, Tomonori*; Ide, Shunsuke; Itami, Kiyoshi; Isayama, Akihiko; Fukuda, Takeshi*

In burning plasmas, the electron temperature $$T_mathrm{e}$$ is expected to exceed the ion temperature $$T_mathrm{i}$$ because of the alpha heating. The transport simulations showed that an increase in $$T_mathrm{e}/T_mathrm{i}$$ degrades the confinement. However in the International Global H-mode Confinement Database, there are data that have the $$H_mathrm{H}$$ factor exceeding unity in the $$T_mathrm{e}>T_mathrm{i}$$ region. This high $$H_mathrm{H}$$ can be attributed mainly to the improved electron confinement. The conditions required for the improvement have been investigated with the local flux-tube gyrokinetic code GS2. When the ion temperature gradient length is shorter than the electron one, ion temperature gradient (ITG) mode is dominant, whereas trapped electron mode (TEM) is stabilized. Under this situation, the electron heat diffusivity is suppressed. In addition, an increase in the magnetic shear also decreases the electron heat transport in the positive shear range.



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