Description
Understanding transport phenomena in plasma systems is critical for optimizing fueling and exhaust processes in fusion devices and explaining angular momentum transport in astrophysical accretion disks. The transport phenomena are traditionally categorized into two distinct paradigms: deterministic convection in laminar flows and stochastic diffusion in turbulent flows. The latter, typically described by Fick’s laws, relies on the assumption of a significant scale separation between microscopic fluctuations and macroscopic profiles. However, in numerous natural and laboratory plasma systems—ranging from magnetic islands in magnetically confined plasmas to drift wave turbulence—this scale separation often breaks down, and the flow field is dominated by large-scale, long-lived coherent structures, leading to distinct transport phenomena.
Inspired by observations of intermittent, bursty, and highly directional transport in magnetized plasma experiments, we propose a deterministic transport mechanism mediated by the topological evolution of the flow field. This study utilizes high-spatiotemporal-resolution diagnostic data from a linear plasma device and employs SVD to extract rotating coherent structures. Our findings reveal that real coherent structures are not ideal rigid bodies; rather, they undergo slow amplitude modulation and multi-mode coupling.Such non-rigid deformation induces a continuous evolution of the instantaneous flow topology, thereby breaking the adiabatic invariants (stream functions) of the ideal Hamiltonian-like system. Specific topological mutations force particles to cross the previously closed separatrix, resulting in deterministic, step-like displacements.