Nondiffusive transport of inertial heavy impurities in drift-wave turbulence

Abstract

We investigate the transport behavior of tungsten impurities with finite inertia in drift-wave turbulence using the Hasegawa-Wakatani model. Unlike previous tracer-based models, our simulations reveal a transition to non-diffusive dynamics for a range of charge states. This novel mechanism offers a turbulence-driven route to core impurity accumulation. This finding underscores the nontrivial role of particle inertia in impurity dynamics and has strong implications for impurity control in future fusion devices.

Figures (4)

• Figure 1: Trajectories for fluid tracers ($St = 0$) and impurity particles with different Stokes numbers are shown. The periodic domain $[0, 64] \times [0, 64]$ has been extended to display continuous trajectories. The common initial position is marked with a green cross.
• Figure 2: Mean square displacement versus time for particles with different Stokes numbers. The inset highlights the long-time regime. Fluid tracers ($St=0$) show ballistic behavior at short times followed by normal diffusion, while particles with higher Stokes numbers exhibit hyperballistic motion at short times and superdiffusive behavior at long times.
• Figure 3: PDFs of trapping times in strongly elliptic regions (vortices) for particles with different Stokes numbers. Fluid tracers ($St=0$) show longer trapping times compared to particles with non-zero Stokes numbers, indicating that inertial effects enable particles to escape vortical trapping more easily.
• Figure 4: Log-log plot of the Rescaled Range (R/S) versus time lag ($\tau$) for different Stokes numbers.