Gyrokinetic simulations of momentum flux parasitic to free-energy transfer

Stoltzfus-Dueck, T. ; Hornsby, W. A.; Grosshauser, S. R.
Issue date: 2022
Rights:
Creative Commons Attribution 4.0 International (CC BY)
Cite as:
Stoltzfus-Dueck, T., Hornsby, W. A., & Grosshauser, S. R. Gyrokinetic simulations of momentum flux parasitic to free-energy transfer [Data set]. Princeton Plasma Physics Laboratory, Princeton University. https://doi.org/10.11578/1888279
@electronic{stoltzfusdueck_t_unknown,
  author      = {Stoltzfus-Dueck, T. and
                Hornsby, W. A. and
                Grosshauser, S. R.},
  title       = {{Gyrokinetic simulations of momentum flux
                 parasitic to free-energy transfer}},
  publisher   = {{Princeton Plasma Physics Laboratory, Pri
                nceton University}},
  url         = {https://doi.org/10.11578/1888279}
}
Description:

Ion Landau damping interacts with a portion of the E×B drift to cause a non-diffusive outward flux of co-current toroidal angular momentum. Quantitative evaluation of this momentum flux requires nonlinear simulations to determine fL, the fraction of fluctuation free energy that passes through ion Landau damping, in fully developed turbulence. Nonlinear gyrokinetic simulations with the GKW code confirm the presence of the systematic symmetry-breaking momentum flux. For simulations with adiabatic electrons, fL scales inversely with the ion temperature gradient, because only the ion curvature drift can transfer free energy to the electrostatic potential. Although kinetic electrons should in principle relax this restriction, the ion Landau damping measured in collisionless kinetic-electron simulations remained at low levels comparable with ion-curvature-drift transfer, except when magnetic shear was strong. A set of simulations scanning the electron pitch-angle scattering rate showed only a weak variation of fL with the electron collisionality. However, collisional-electron simulations with electron temperature greater than ion temperature unambiguously showed electron-curvature-drift transfer supporting ion Landau damping, leading to a corresponding enhancement of the symmetry-breaking momentum flux.

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