Effect of multi-scale interactions among the edge turbulence, geodesic acoustic mode and <i>m</i> / <i>n</i> = 3/1 tearing mode on plasma confinement and transport in J-TEXT tokamak

Abstract The effects of multi-scale interactions among the edge turbulence, geodesic acoustic mode (GAM) and tearing mode (TM) on the plasma confinement and transport under the positive bias (+300 V) are investigated in the edge plasma of J-TEXT tokamak. The experimental results show that with the positive bias, the central line-averaged density increases and H α emission decreases, which indicates the improvement of global particle confinement. Simultaneously, in the edge plasma, the low-frequency turbulence, TM and turbulent particle transport flux are found to be suppressed by a strong mean flow shear induced by the bias. Besides, the high-frequency turbulence (50–400 kHz) is modulated by both the TM and GAM. The wavelet-bispectrum analysis demonstrates the existence of nonlinear three-wave interactions among the turbulence, GAM and TM. In addition, the transfer entropy analysis shows that although the potential turbulence can directly influence the GAM by driving the Reynolds stress, it primarily regulates the magnetic fluctuation thereby affecting the GAM. It is also found that both the TM and GAM can affect the density turbulence and particle transport. And th effect of TM on the particle transport is stronger than that of GAM. As expected, a strong direct influence of the density turbulence on the particle transport is verified, which indicates that the regulation of transport by the TM and GAM is primarily mediated by the density turbulence.These results contribute to a deeper understanding of the impact of electromagnetic multi-scale interactions on the plasma confinement and transport in fusion plasmas.