Hyperdiffusion of dust particles in a turbulent tokamak plasma

Nespoli, Federico; Kaganovich, Igor; Autricque, Adrien; Marandet, Yannick; Tamain, Patrick
Issue date: July 2021
Cite as:
Nespoli, Federico, Kaganovich, Igor, Autricque, Adrien, Marandet, Yannick, & Tamain, Patrick. (2021). Hyperdiffusion of dust particles in a turbulent tokamak plasma [Data set]. Physics of Plasma.
  author      = {Nespoli, Federico and
                Kaganovich, Igor and
                Autricque, Adrien and
                Marandet, Yannick and
                Tamain, Patrick},
  title       = {{Hyperdiffusion of dust particles in a tu
                rbulent tokamak plasma}},
  publisher   = {{Physics of Plasma}},
  year        = 2021

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.

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# Filename Description Filesize
1 data_for_fig_PoP2021.zip data archive 1.77 GB
2 README.txt readme file 1.92 KB