Electron-scale micro-turbulence driven by the electron temperature gradient (ETG) instability has recently been shown to impact the electron heat transport in tokamaks. Given the relevance of these mechanisms for ITER scenarios, a new study has been carried out on the TCV tokamak at the Swiss Plasma Center, which is equipped with both electron cyclotron heating (ECH) and neutral beam injection (NBI) heating, allowing investigation of the relevance of ETG transport. Dedicated L-mode TCV discharges have been performed and the experimental measurements have been compared with gyrokinetic simulations. The results indicate that ETGs should contribute to electron heat transport from mid-radius to the edge when NBI and ECH are simultaneously applied, while the cases with pure ECH are dominated by ion-scale turbulence at mid-radius and show signs of possible ETG contribution only at outer radii.
Formation of electron internal transport barriers by highly localized electron cyclotron resonance heating in the large helical device