@article{879a6f3bcf8548839b72fe0939834af8,
title = "A phase-shift-periodic parallel boundary condition for low-magnetic-shear scenarios",
abstract = "We formulate a generalized periodic boundary condition as a limit of the standard twist-and-shift parallel boundary condition that is suitable for simulations of plasmas with low magnetic shear. This is done by applying a phase shift in the binormal direction when crossing the parallel boundary. While this phase shift can be set to zero without loss of generality in the local flux-tube limit when employing the twist-and-shift boundary condition, we show that this is not the most general case when employing periodic parallel boundaries, and may not even be the most desirable. A non-zero phase shift can be used to avoid the convective cells that plague simulations of the three-dimensional Hasegawa-Wakatani system, and is shown to have measurable effects in periodic low-magnetic-shear gyrokinetic simulations. We propose a numerical program where a sampling of periodic simulations at random pseudo-irrational flux surfaces are used to determine physical observables in a statistical sense. This approach can serve as an alternative to applying the twist-and-shift boundary condition to low-magnetic-shear scenarios, which, while more straightforward, can be computationally demanding.",
keywords = "gyrokinetics, magnetic shear, numerical methods",
author = "St-Onge, {D. A.} and M. Barnes and Parra, {F. I.}",
note = "Funding Information: The authors would like to thank Plamen G Ivanov for many fruitful discussions. This work has been carried out within the framework of the EUROfusion Consortium, funded by the European Union via the Euratom Research and Training Programme (Grant Agreement No. 101052200 - EUROfusion). Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Commission. Neither the European Union nor the European Commission can be held responsible for them. This work was supported in part by the Engineering and Physical Sciences Research Council (EPSRC) (Grant No. EP/R034737/1). The authors acknowledge EUROfusion, the EUROfusion High Performance Computer (Marconi-Fusion) under the project MULTEI and OXGK, and the use of ARCHER through the Plasma HEC Consortium (EPSRC Grant No. EP/R029148/1) under the Project e607. This work was also supported by the U.S. Department of Energy under Contract No. DE-AC02-09CH11466. The United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. Publisher Copyright: {\textcopyright} 2022 The Author(s). Published by IOP Publishing Ltd.",
year = "2023",
month = jan,
day = "1",
doi = "10.1088/1361-6587/aca4f8",
language = "English (US)",
volume = "65",
journal = "Plasma Physics and Controlled Fusion",
issn = "0741-3335",
publisher = "IOP Publishing Ltd.",
number = "1",
}