U.S. Department of EnergyOffice of Scientific and Technical Information
Hyperdiffusion of dust particles in a turbulent tokamak 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.
- Authors:
-
- Princeton University (PPPL)
- Publication Date:
- DOE Contract Number:
- AC02-09CH11466
- Research Org.:
- Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States)
- Sponsoring Org.:
- USDOE Office of Science (SC)
- Subject:
- dust; plasma turbulence; simulations; transport
- OSTI Identifier:
- 1814957
- DOI:
- https://doi.org/10.11578/1814957
Citation Formats
Nespoli, Federico, Kaganovich, Igor, Autricque, Adrien, Marandet, Yannick, and Tamain, Patrick. Hyperdiffusion of dust particles in a turbulent tokamak plasma. United States: N. p., 2021.
Web. doi:10.11578/1814957.
Nespoli, Federico, Kaganovich, Igor, Autricque, Adrien, Marandet, Yannick, & Tamain, Patrick. Hyperdiffusion of dust particles in a turbulent tokamak plasma. United States. doi:https://doi.org/10.11578/1814957
Nespoli, Federico, Kaganovich, Igor, Autricque, Adrien, Marandet, Yannick, and Tamain, Patrick. 2021.
"Hyperdiffusion of dust particles in a turbulent tokamak plasma". United States. doi:https://doi.org/10.11578/1814957. https://www.osti.gov/servlets/purl/1814957. Pub date:Thu Jul 08 00:00:00 EDT 2021
@article{osti_1814957,
title = {Hyperdiffusion of dust particles in a turbulent tokamak plasma},
author = {Nespoli, Federico and Kaganovich, Igor and Autricque, Adrien and Marandet, Yannick and Tamain, Patrick},
abstractNote = {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.},
doi = {10.11578/1814957},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Thu Jul 08 00:00:00 EDT 2021},
month = {Thu Jul 08 00:00:00 EDT 2021}
}