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Title: | Hyperdiffusion of dust particles in a turbulent tokamak plasma |
Contributors: | Nespoli, Federico Kaganovich, Igor Autricque, Adrien Marandet, Yannick Tamain, Patrick |
Keywords: | plasma turbulence dust simulations transport |
Issue Date: | Jul-2021 |
Publisher: | Physics of Plasma |
Abstract: | 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. |
URI: | http://arks.princeton.edu/ark:/88435/dsp01db78tg111 |
Appears in Collections: | Other Projects |
Files in This Item:
File | Description | Size | Format | |
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data_for_fig_PoP2021.zip | data archive | 1.86 GB | Unknown | View/Download |
README.txt | readme file | 1.92 kB | Text | View/Download |
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