TY - JOUR
T1 - Continuous-in-time approach to flow shear in a linearly implicit local δf gyrokinetic code
AU - Christen, Nicolas
AU - Barnes, Michael
AU - Parra, Felix I.
N1 - Funding Information:
The authors would like to thank H. Weisen and P. Sirén for providing the data of the JET shot analysed in § 4.3. They would also like to thank M. R. Hardman, O. Beeke, J. Ball and P. J. Dellar for very useful discussions. The GS2 branch that includes the continuous-in-time algorithm in the presence of flow shear is available at https://bitbucket.org/gyrokinetics/gs2/branch/ndc_branch with the latest commit at the time of writing being 0abdcda. The corresponding ‘Makefiles’ branch can be found at https://bitbucket.org/gyrokinetics/makefiles/branch/ndc_branch with the commit ba24979, and the corresponding ‘utils’ branch is available at https://bitbucket.org/gyrokinetics/utils/branch/ndc_branch with the commit 8e41f9a. This work was supported by the Berrow Foundation (scholarship of N.C.); the Steppes Fund for Change (scholarship of N.C.); the Fondation Hélène et Victor Barbour (scholarship of N.C.); Lincoln College, Oxford; the Department of Physics of the University of Oxford; and EPSRC (grant EP/R034737/1). The authors also acknowledge the use of the ARCHER High Performance Computer through the Plasma HEC Consortium EPSRC (grant EP/L000237/1 under project e281-gs2); the EUROfusion High Performance Computer (Marconi-Fusion, projects FUA32_MULTEI, FUA33_MULTEI and FUA34_MULTEI); and the high performance computing cluster Hydra at the Theoretical Physics subdepartment of the University of Oxford.
Publisher Copyright:
© The Author(s), 2021.
PY - 2021/4
Y1 - 2021/4
N2 - A new algorithm for toroidal flow shear in a linearly implicit, local δf gyrokinetic code is described. Unlike the current approach followed by a number of codes, it treats flow shear continuously in time. In the linear gyrokinetic equation, time-dependences arising from the presence of flow shear are decomposed in such a way that they can be treated explicitly in time with no stringent constraint on the time step. Flow shear related time dependences in the nonlinear term are taken into account exactly, and time dependences in the quasineutrality equation are interpolated. Test cases validating the continuous-in-time implementation in the code GS2 are presented. Lastly, nonlinear gyrokinetic simulations of a JET discharge illustrate the differences observed in turbulent transport compared with the usual, discrete-in-time approach. The continuous-in-time approach is shown, in some cases, to produce fluxes that converge to a different value than with the discrete approach. The new approach can also lead to substantial computational savings by requiring radially narrower boxes. At fixed box size, the continuous implementation is only modestly slower than the previous, discrete approach.
AB - A new algorithm for toroidal flow shear in a linearly implicit, local δf gyrokinetic code is described. Unlike the current approach followed by a number of codes, it treats flow shear continuously in time. In the linear gyrokinetic equation, time-dependences arising from the presence of flow shear are decomposed in such a way that they can be treated explicitly in time with no stringent constraint on the time step. Flow shear related time dependences in the nonlinear term are taken into account exactly, and time dependences in the quasineutrality equation are interpolated. Test cases validating the continuous-in-time implementation in the code GS2 are presented. Lastly, nonlinear gyrokinetic simulations of a JET discharge illustrate the differences observed in turbulent transport compared with the usual, discrete-in-time approach. The continuous-in-time approach is shown, in some cases, to produce fluxes that converge to a different value than with the discrete approach. The new approach can also lead to substantial computational savings by requiring radially narrower boxes. At fixed box size, the continuous implementation is only modestly slower than the previous, discrete approach.
KW - fusion plasma
KW - plasma simulation
UR - http://www.scopus.com/inward/record.url?scp=85105602032&partnerID=8YFLogxK
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U2 - 10.1017/S0022377821000453
DO - 10.1017/S0022377821000453
M3 - Article
AN - SCOPUS:85105602032
SN - 0022-3778
VL - 87
JO - Journal of Plasma Physics
JF - Journal of Plasma Physics
IS - 2
M1 - 905870230
ER -