7th Asia-Pacific Conference on Plasma Physics, 12-17 Nov, 2023 at Port Messe Nagoya

Cross-Verification Study of Gyrokinetic Codesfor the L-mode discharge in KSTAR
1

C. Sung , E. S. Yoon2, D. Kim1, T. Moon2, J. Kang3, M. W. Lee1, S. Yi3, J.-M. Kwon3
1
Department of Nuclear and Quantum Engineering, KAIST,
2
Department of Nuclear Engineering, UNIST, 3Korea Institute of Fusion Energy (KFE)e-mail (speaker): choongkisung@kaist.ac.kr
Gyrokinetic codes have been employed to investigate
the physical mechanisms underlying the turbulence
stabilization by fast ions in fusion plasmas [1]. However,despite decades of extensive verification studies for
gyrokinetic codes [2], the fast ion effects on turbulence
predicted by gyrokinetic codes have not been verified.
This motivated our cross-verification study, wherein wecompared linear and nonlinear simulation results fromtwo widely-used gyrokinetic codes in the fusion
community, GENE [3] and CGYRO [4]. The study wasconducted on a neutral beam injection (NBI)-heated
L-mode discharge in KSTAR, where fast ion effects canbe investigated. Additionally, we sought to verify
gyrokinetic predictions of the rotation effects on
turbulence, as previous research indicated discrepancies
among gyrokinetic codes in nonlinear simulation results[5].
For our verification study, we considered four cases
based on the inclusion of rotation and fast ion effects, as
shown in Table 1. At r/a=0.5 (where a is the minorradius), linear stability analysis was performed for cases
I-IV, as depicted in Fig. 1. In all cases, the most unstablemode exhibited a positive real frequency, which indicatesthe electric diamagnetic direction in this study, in both
GENE and CGYRO results. Good agreement between
CGYRO and GENE results was observed in case I. The
inclusion of rotation effects (case II) showed consistentresults, with both codes matching within ~0.02 [cs/a]
where cs is a sound speed of the main ion. 5%.
Furthermore, both codes predicted the reduction of linear
growth rate and the appearance of a long-wavelength ion
mode with the addition of fast ions (cases III and IV,
compared to cases I and II). However, a discrepancy inthe growth rate of the long-wavelength ion mode wasobserved when fast ions were included. Overall, weobserved a good agreement in the real frequency of themost unstable mode regardless of the inclusion ofrotation effects and fast ions while the inclusion of fastions can result in discrepancy in the linear growth rate of
the long-wavelength mode, which can be relevant to thefast ion mode.
Case I
Case II
Case III
Case IV

Rotation
XO
XO

Fast ionXXOOTable 1 Four cases used in the verification study

In this presentation, we will also compare nonlinear
simulation results between two codes, analyzing theirpredicted energy fluxes and turbulence structures.
Additionally, we will discuss the discrepancies observed
between the results of the two codes.

Figure 1 Real frequency (left) and linear growth rate (right)of the most unstable mode for case I to IV predicted by
GENE (red) and CGYRO (blue)

Computing resources were provided by the National
Supercomputing Center with supercomputing resources
including technical support (KSC-2022-CRE-0161, KSC-2022-CRE-0392, KSC-2023-CRE-0075) and on theKFE computer KAIROS, funded by the Ministry ofScience and ICT of the Republic of Korea (KFEEN2241)
References[1] J. Citrin and P. Mantica, Plasma Phys. Control.
Fusion 65 033001 (2023)[2] A. White, J. Plasma Phys., 85 925850102 (2019)[3] F. Jenko, et al., Phys. Plasmas 7 1904 (2000)[4] J. Candy, et al., J. Comput. Phys., 324, 73 (2016)[5] D. Mikkelsen, et al., Phys. Plasmas 25 042505 (2018)