Strong electron temperature stiffness induced by broad-band turbulence in high poloidal beta plasmas on EAST

We report observations of strong electron temperature profile stiffness in high poloidal beta ( β p ∼ 2 ) plasmas on EAST for the first time. Key features of this regime include: (1) Negligible contributions to stored energy and electron temperature from additional auxilliary heating power; and (2) a rapid increase of core broad-band turbulence ( k θ ρ s ∼ 1 − 5 , f ∼ 0 − 2000 kHz ) monitored by collective Thomson scattering (CTS) diagnostic system. Notably, no significant increase in impurities or MHD activities are observed during this process. This strong stiffness can be interpreted as a nonlinear increase in turbulent thermal flux when temperature gradients exceed a critical threshold. Gyro-kinetic simulations show that trapped electron mode is responsible for the enhanced broad-band turbulence observed in the core. The experimental electron heat fluxes are well matched by the nonlinear electromagnetic simulations for the high heating power case, whereas larger discrepancies between the simulations and experiments are observed for the low heating power case. This finding highlights the advantages of using CTS to detect microturbulence in the core of high-density plasmas, allowing for immediate identification of profile stiffness induced by turbulence.