Electron-scale turbulence, whose wavelength is the electron Larmor radius, is thought to have the potential to cause stiffness in an 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 , were investigated. The electron temperature gradient was successfully varied in the range of by controlling the injection power of on/off-axis electron cyclotron heating. The results show a significant increase in the electron-scale turbulence with increasing , especially in conditions where Electron Temperature Gradient (ETG) instability is linearly unstable, suggesting the presence of ETG turbulence at high . The electron heat flux also increases steeply with increasing . In addition, the electron-scale turbulence is observed even at , which is stable in linear GKV calculations. Finding the cause of this phenomenon is an interesting task for the future.
This paper investigates the relationship between electron-scale turbulence and the electron temperature gradient in the Large Helical Device (LHD). The results show that as the electron temperature gradient increases, the electron-scale turbulence and heat flux also increase, especially when the Electron Temperature Gradient (ETG) instability is linearly unstable. This suggests the presence of ETG turbulence at high electron temperature gradients, which can degrade the confinement of future fusion reactors.