Turbulence Analyses of Improved Electron Energy Confinement in H-Mode Plasmas with Gyrokinetic Calculations

Abstract

In the International Global H-mode Confinement Database, there are data that have the H_H98(y,2) factor exceeding unity in the region where the electron temperature is higher than the ion one. This high value of H_H98(y,2) can be attributed mainly to the improved electron confinement. The conditions required for this improvement are 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 effect of the magnetic shear s is also studied in the positive shear range, 0.6 ≤ s ≤ 1.4, and the reduction in the electron and ion heat transport with increasing s is found.