Long radial coherence of electron temperature fluctuations in non-local transport in HL-2A plasmas

Abstract

The dynamics of long-wavelength ($k_{\theta }<1.4\mathrm{c}{\mathrm{m}}^{-1}$), broadband (20-200 kHz) electron temperature fluctuations (${\tilde{T}}_e/T_e$) of plasmas in gas-puff experiments were observed for the first time in HL-2A tokamak. In a relative low density ($n_e(0)\simeq 0.91\sim 1.20\times 10^{19}/m^3$) scenario, after gas-puffing the core temperature increases and the edge temperature drops. On the contrary, temperature fluctuation drops at the core and increases at the edge. Analyses show the non-local emergence is accompanied with a long radial coherent length of turbulent fluctuations. While in a higher density ($n_e(0)\simeq 1.83\sim 2.02\times 10^{19}/m^3$) scenario, the phenomena were not observed. Furthermore, compelling evidence indicates that $\text{E}\times \text{B}$ shear serves as a substantial contributor to this extensive radial interaction. This finding offers a direct explanatory link to the intriguing core-heating phenomenon witnessed within the realm of non-local transport.