Eliminating turbulent self-interaction through the parallel boundary condition in local gyrokinetic simulations

Abstract

In this work, we highlight an issue that may reduce the accuracy of many local nonlinear gyrokinetic simulations - turbulent self-interaction through the parallel boundary condition. Given a sufficiently long parallel correlation length, individual turbulent eddies can span the full domain and "bite their own tails," thereby altering their statistical properties. Such self-interaction is only modeled accurately when the simulation domain corresponds to a full flux surface, otherwise it is artificially strong. For Cyclone Base Case parameters and typical domain sizes, we find that this mechanism modifies the heat flux by roughly 40% and it can be even more important. The effect is largest when using kinetic electrons, low magnetic shear, and strong turbulence drive (i.e. steep background gradients). It is found that parallel self-interaction can be eliminated by increasing the parallel length and/or the binormal width of the simulation domain until convergence is achieved.

arXiv comment19 pages, 9 figures

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Cited by in corpus (9)

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• Local gyrokinetic simulations of tokamaks with non-uniform magnetic shear
• A non-twisting flux tube for local gyrokinetic simulations
• Ultra Long Turbulent Eddies, Magnetic Topology, and the Triggering of Internal Transport Barriers in Tokamaks
• A novel approach to radially global gyrokinetic simulation using the flux-tube code $\text{stella}$
• Microtearing turbulence saturation via electron temperature flattening at low-order rational surfaces
• Effect of collisions on non-adiabatic electron dynamics in ITG-driven microturbulence
• A phase-shift-periodic parallel boundary condition for low-magnetic-shear scenarios