Transport characteristics of trapped-electron-mode turbulence nonlinearly interacting with tearing modes in tokamak plasmas

Turbulent transport in tokamak plasmas is strongly affected by changes in magnetic topology associated with magnetic islands (MIs). To examine how dynamic MIs generated by intrinsic instabilities, such as the resistive tearing mode (RTM), influence transport, we perform simulations of the nonlinear interaction between trapped-electron-mode (TEM) turbulence and RTM fluctuations using a compact gyro-Landau fluid model. Our simulations reveal novel oscillatory transport dynamics in multi-mode, multi-scale turbulence. Under moderate TEM and RTM instability, turbulent particle and heat fluxes display oscillatory behavior. In particular, periodic bursts of electron heat flux are linked to the repeated formation and evolution of m/n = 2/1 MIs (where m and n denote the poloidal and toroidal mode numbers, respectively). At the same time, the ion heat flux alternates between inward (thermal pinch) and outward (thermal diffusion) transport. When the RTM becomes more unstable, the ion heat flux can shift to predominantly inward transport with periodic oscillations. The oscillation timescale is comparable to trapped-electron precession drift frequency, while its amplitude depends on the relative strength of TEM and RTM instabilities, which are governed by plasma parameters such as β, resistivity, and viscosity. Analysis of the transport response to dynamic MIs shows that the 2/1 mode is periodically excited through alternating phases of magnetic reconnection and island shrinkage, leading to cyclic transitions of the n = 1 RTM eigenmodes. Meanwhile, the 3/1 mode, associated with nearly stationary islands of finite width, modulates these cycles through toroidal coupling with the neighboring 2/1 mode. These results offer new insight into the intermittent or oscillatory transport observed in tokamak plasmas with dynamic MIs and provide connections to experimental observations.