Synergistic cross-scale coupling of turbulence in a tokamak plasma
Author(s)Howard, Nathaniel Thomas; Holland, C.; Candy, J.; Greenwald, Martin J.; White, Anne E.
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For the first time, nonlinear gyrokinetic simulations spanning both the ion and electron spatio-temporal scales have been performed with realistic electron mass ratio ((m[subscript D] [over m [subscript e])[superscript 1 over 2] = 60.0), realistic geometry, and all experimental inputs, demonstrating the coexistence and synergy of ion (k[subscript θρs] ~O(1.0)) and electron-scale (k[subscript θρe] ~O(1.0)) turbulence in the core of a tokamak plasma. All multi-scale simulations utilized the GYRO code [J. Candy and R. E. Waltz, J. Comput. Phys. 186, 545 (2003)] to study the coupling of ion and electron-scale turbulence in the core (r/a = 0.6) of an Alcator C-Mod L-mode discharge shown previously to exhibit an under-prediction of the electron heat flux when using simulations only including ion-scale turbulence. Electron-scale turbulence is found to play a dominant role in setting the electron heat flux level and radially elongated (k[subscript r] ≪ k[subscript θ]) “streamers” are found to coexist with ion-scale eddies in experimental plasma conditions. Inclusion of electron-scale turbulence in these simulations is found to increase both ion and electron heat flux levels by enhancing the transport at the ion-scale while also driving electron heat flux at sub-ρ[subscript i] scales. The combined increases in the low and high-k driven electron heat flux may explain previously observed discrepancies between simulated and experimental electron heat fluxes and indicates a complex interaction of short and long wavelength turbulence.
DepartmentMassachusetts Institute of Technology. Department of Nuclear Science and Engineering; Massachusetts Institute of Technology. Plasma Science and Fusion Center
Physics of Plasmas
American Institute of Physics (AIP)
Howard, N. T., C. Holland, A. E. White, M. Greenwald, and J. Candy. “Synergistic Cross-Scale Coupling of Turbulence in a Tokamak Plasma.” Phys. Plasmas 21, no. 11 (November 2014): 112510.