TY - JOUR

T1 - A hybrid gyrokinetic ion and isothermal electron fluid code for astrophysical plasma

AU - Kawazura, Y.

AU - Barnes, M.

N1 - Funding Information:
This work was supported by STFC grant ST/N000919/1 . We thank A. A. Schekochihin and D. Grošelj for useful discussions. The authors also acknowledge the use of ARCHER through the Plasma HEC Consortium EPSRC grant number EP/L000237/1 under the projects e281-gs2 and the use of the University of Oxford Advanced Research Computing (ARC) facility.
Publisher Copyright:
© 2018 Elsevier Inc.

PY - 2018/5/1

Y1 - 2018/5/1

N2 - This paper describes a new code for simulating astrophysical plasmas that solves a hybrid model composed of gyrokinetic ions (GKI) and an isothermal electron fluid (ITEF) Schekochihin et al. (2009) [9]. This model captures ion kinetic effects that are important near the ion gyro-radius scale while electron kinetic effects are ordered out by an electron–ion mass ratio expansion. The code is developed by incorporating the ITEF approximation into AstroGK, an Eulerian δf gyrokinetics code specialized to a slab geometry Numata et al. (2010) [41]. The new code treats the linear terms in the ITEF equations implicitly while the nonlinear terms are treated explicitly. We show linear and nonlinear benchmark tests to prove the validity and applicability of the simulation code. Since the fast electron timescale is eliminated by the mass ratio expansion, the Courant–Friedrichs–Lewy condition is much less restrictive than in full gyrokinetic codes; the present hybrid code runs ∼2mi/me∼100 times faster than AstroGK with a single ion species and kinetic electrons where mi/me is the ion–electron mass ratio. The improvement of the computational time makes it feasible to execute ion scale gyrokinetic simulations with a high velocity space resolution and to run multiple simulations to determine the dependence of turbulent dynamics on parameters such as electron–ion temperature ratio and plasma beta.

AB - This paper describes a new code for simulating astrophysical plasmas that solves a hybrid model composed of gyrokinetic ions (GKI) and an isothermal electron fluid (ITEF) Schekochihin et al. (2009) [9]. This model captures ion kinetic effects that are important near the ion gyro-radius scale while electron kinetic effects are ordered out by an electron–ion mass ratio expansion. The code is developed by incorporating the ITEF approximation into AstroGK, an Eulerian δf gyrokinetics code specialized to a slab geometry Numata et al. (2010) [41]. The new code treats the linear terms in the ITEF equations implicitly while the nonlinear terms are treated explicitly. We show linear and nonlinear benchmark tests to prove the validity and applicability of the simulation code. Since the fast electron timescale is eliminated by the mass ratio expansion, the Courant–Friedrichs–Lewy condition is much less restrictive than in full gyrokinetic codes; the present hybrid code runs ∼2mi/me∼100 times faster than AstroGK with a single ion species and kinetic electrons where mi/me is the ion–electron mass ratio. The improvement of the computational time makes it feasible to execute ion scale gyrokinetic simulations with a high velocity space resolution and to run multiple simulations to determine the dependence of turbulent dynamics on parameters such as electron–ion temperature ratio and plasma beta.

KW - Gyrokinetics

KW - Isothermal electron fluid

KW - Kinetic–fluid hybrid

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U2 - 10.1016/j.jcp.2018.01.026

DO - 10.1016/j.jcp.2018.01.026

M3 - Article

AN - SCOPUS:85041632968

SN - 0021-9991

VL - 360

SP - 57

EP - 73

JO - Journal of Computational Physics

JF - Journal of Computational Physics

ER -