Electron ITB formation in EAST high poloidal beta plasmas under dominant electron heating

Abstract Plasma confinement and transport in tokamaks play a crucial role in the development of high poloidal beta steady-state operation scenario. So, it is very important to study the relevant mechanism of internal transport barriers (ITBs), which can help plasmas to obtain better confinement in order to get higher fusion gain. This paper mainly introduces the analysis of the characteristics of electron heat transport of discharges with ITB in high βp operation regime on EAST. Based on the statistical analysis of stable discharges with βp > 1.5, it is found that there is an obvious bifurcation of the normalized electron temperature gradient (R/LTe) in the range of βp = 2~2.2. Then, the discharges of lower βp(βp < 2, the value of βp is below the bifurcation threshold) and of higher βp (βp> 2.2,the value of βp is above the threshold) were selected for analysis. The diagnostic data provided by Thomson Scattering, X-ray Crystal Spectrometer and Charge eXchange Recombination Spectroscopy are used to provide reliable parameter profiles , and then combined with the data of external magnetic probe measurements and the POlarization INTerferometer diagnosis system to fully reconstruct the balance. Relevant plasma current calculation model is used to calculate and analyse the current density profiles and power deposition, and then the transport analysis is carried out. Interestingly, in the higher βp discharges, it is found that the turbulence intensity provided by CO2 laser collective scattering system gradually decreases and the normalized electron temperature gradient R/LTe gradually increases. It is also found that the electron heat transport coefficient is decreased in the discharge with higher βp and the growth rate of the electron-scale turbulence calculated by TGLF is significantly reduced. Meanwhile, similar conclusions are also obtained in the discharges with the βp further increased.