Electron-scale turbulence characteristics with varying electron temperature gradient in LHD

Abstract

The electron-scale turbulence, whose wavelength is about the electron Larmor radius, is thought to have the potential to cause the stiffness of the electron temperature gradient and degrade the confinement of future burning plasma in which the electron heating by alpha particles is dominant. The dependence of electron-scale turbulence and electron heat flux on the electron temperature inverse gradient length Rax/LTe were investigated. The electron temperature gradient is successfully varied in the range of −3 < Rax/LTe < 12 by controlling the injection power of the on/off-axis electron cyclotron heating. The results show a significant increase in electron-scale turbulence with increasing Rax/LTe, especially in conditions where the Electron Temperature Gradient (ETG) instability is linearly unstable, suggesting the presence of ETG turbulence at high Rax/LTe. The electron heat flux also increases steeply with increasing Rax/LTe. In addition, electron-scale turbulence is observed even at Rax/LTe ∼ 0, which is stable in linear GKV calculations. Finding the cause of this phenomenon is an interesting task for the future.