Hyperdiffusion of dust particles in a turbulent tokamak plasma

Dataset · Thu Jul 08 04:00:00 EDT 2021

DOI:https://doi.org/10.11578/1814957· OSTI ID:1814957

Nespoli, Federico ^[1]; Kaganovich, Igor; Autricque, Adrien; Marandet, Yannick; Tamain, Patrick

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1. Princeton University (PPPL)

The effect of plasma turbulence on the trajectories of dust particles is investigated for the first time. The dynamics of dust particles is computed using the ad-hoc developed Dust Injection Simulator code, using a 3D turbulent plasma background computed with the TOKAM3X code. As a result, the evolution of the particle trajectories is governed by the ion drag force, and the shape of the trajectory is set by the Stokes number $$St\propto a_d/n_0$$, with $$a_d$$ the dust radius and $$n_0$$ the density at the separatrix. The plasma turbulence is observed to scatter the dust particles, exhibiting a hyperdiffusive regime in all cases. The amplitude of the turbulent spread of the trajectories $$\Delta r^2$$ is shown to depend on the ratio $Ku/St$, with $$Ku\propto u_{rms}$$ the Kubo number and $$u_{rms}$$ the fluctuation level of the plasma flow. These results are compared with a simple analytical model, predicting $$\Delta r^2\propto (Ku/St)^2t^3$$, or $$\Delta r^2\propto (u_{rms}n_0/a_d)^2t^3$$. As the dust is heated by the plasma fluxes, thermionic emission sets the dust charge, originally negative, to slightly positive values. This results in a substantial reduction of the ion drag force through the suppression of its Coulomb scattering component. The dust grain inertia is then no longer negligible, and drives the transition from a hyperdiffusive regime towards a ballistic one.

• Research Organization: Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States)
• Sponsoring Organization: USDOE Office of Science (SC)
• DOE Contract Number: AC02-09CH11466
• OSTI ID: 1814957
• Country of Publication: United States
• Language: English

Related Subjects

dust
plasma turbulence
simulations
transport