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

Turbulent transport behavior is often influenced by changes in magnetic topology caused by the formation of magnetic islands (MIs) in tokamak plasmas. To investigate the impact of dynamic MIs arising from intrinsic instabilities, such as the resistive tearing mode (RTM), on transport properties, we carry out self-consistent simulations of the nonlinear coupling between trapped electron mode (TEM) turbulence and RTM fluctuations using a compact Landau fluid model. Results reveal novel transport dynamics emerging in multi-mode, multi-scale turbulence. In particular, the turbulent particle and heat fluxes exhibit oscillatory transport behavior under moderate TEM and RTM instabilities. Notably, periodic bursts of turbulent electron heat flux are identified, corresponding to the recurring formation and evolution of m/n=2/1 MIs (where m and n denote the poloidal and toroidal mode numbers, respectively). Simultaneously, turbulent ion heat transport alternates between inward heat flux (thermal pinch) and outward heat flux (thermal diffusion). Under more unstable RTM conditions, the ion heat flux may transition to a predominantly inward direction, with periodic oscillation. The timescale of this oscillatory transport is estimated to correspond to the precession drift frequency of trapped electrons, and the amplitude is found to depend on the relative strength of the TEM and RTM instabilities, which are closely connected to plasma profiles and parameters such as plasma β, resistivity, and viscosity. The underlying physical mechanisms governing these phenomena are explored by examining the turbulent transport response to dynamic MIs. It is shown that the 2/1 mode is periodically excited, accompanied by alternating phases of magnetic reconnection and island shrinkage, resulting in cyclic state transitions of the n=1 RTM eigenmodes. Concurrently, the 3/1 mode, characterized by nearly stationary MIs of a specific width, plays a crucial role in modulating these cycles through toroidal mode coupling with the adjacent 2/1 mode. These findings provide new insights into understanding the transport intermittency or oscillatory transport phenomena observed in tokamak plasmas with dynamic MIs, offering connections to experimental observations