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

Cross-scale interactions between trapped electron mode andelectron-temperature-gradient-driven turbulence

Shinya Maeyama1, Tomo-Hiko Watanabe1, Shaokang Xu2, Motoki Nakata3
1
Department of Physics, Nagoya University, 2 Southwestern Institute of Physics, 3 National
Institute for Fusion Sciencee-mail (speaker): smaeyama@p.phys.nagoya-u.ac.jp
Plasma turbulence and micro-instabilities arecharacterized by small spatial scales, on the order of theelectron or ion gyro-radii. Recent studies of cross-scaleinteractions between electron and ion-scale turbulence
make significant progress. The importance of cross-scaleinteractions or electron-scale effects was reported fromexperiments in Alcator C-Mod [1], DIII-D[2], JET,ASDEX-Upgrade, and TCV [3].
In this study, we report on the results of numericalsimulations by using the gyrokinetic Vlasov simulation
code GKV [4] on the supercomputer Fugaku. This isprogress from our latest publication [5], which carriedout multi-scale turbulence simulations of high electron
temperature plasma including trapped electron modes(TEM) and electron-temperature-gradient (ETG) modes.
First, the impact of cross-scale interactions on particle
transport has been investigated. Fig. 1a plots thecomparison of deuterium particle fluxes in multi-scale,ion-scale, and electron-scale simulations. Multi-scale andelectron-scale simulations agree well at Te/Ti < 2 where
the dominant instability is ETG modes. On the otherhand, Multi-scale and ion-scale simulations agree well atTe/Ti=4 where TEMs dominate. Significant cross-scaleinteractions were observed at Te/Ti=3, where TEM
turbulence is suppressed in the presence of ETG
turbulence. At the same time, the perturbed gyrokinetic
simulation rigorously satisfies the ambipolar diffusion
condition, 1 = ∑𝑠𝑠 𝑍𝑍𝑠𝑠 Γ𝑠𝑠 /Γ𝑒𝑒 , where Zs is the charge
number and Γs is the particle flux of the species s. Since
the present simulation contains electrons, fuel deuterium
and tritium ions, and helium ash, we have examined thedetailed breakdown of the ambipolar diffusion conditionin Fig 2b. By comparing the breakdowns with those ofelectron-scale or ion-scale simulations, we found that themain impact of cross-scale interaction was themodification of turbulent amplitude, but not the changeof the breakdown of each species.
Second, we have also carried out multi-scale
TEM/ETG simulations with employing JT-60U
experimental equilibrium profile. We observed thesuppression of TEM turbulence by ETG turbulence, as
well as our previous works in analytic magnetic
geometry [5,6]. This suggests that the stabilization ofTEM by ETG can play a role in the evaluation ofexperimental transport levels.
References[1] HOWARD, N.T., HOLLAND, C., WHITE, A.E., etal., Nucl. Fusion 56 (2016) 014004.
[2] HOWARD, N.T., HOLLAND, C., RHODES, T.L.,
et al., Nucl. Fusion 61 (2021) 106002.
[3] MARIANI, A., BONANOMI, N., MANTICA, P., etal., Nucl. Fusion 61 (2021) 116071.
[4] WATANABE, T.-H., SUGAMA, H, Nucl. Fusion
46 (2006) 24-32.
[5] MAEYAMA, S., WATANABE, T.-H., NAKATA,M., et al., Nat. Commun. 13 (2022) 3166.
[6] WATANABE, T.-H., MAEYAMA, S., NAKATA,M., Nucl. Fusion 63 (2023) 054001.
[7] NAKATA, M., HONDA, M., YOSHIDA, M., et al.,Nucl. Fusion 56 (2016) 086010.

Figure 1. (a) Comparison of deuterium particle fluxes in multi-scale, ion-scale, and electron-scale simulations asfunctions of electron-to-ion temperature ratio. (b) Breakdown of ambipolar diffusion condition 1 = ∑𝑠𝑠=𝐷𝐷,𝑇𝑇,𝐻𝐻𝐻𝐻 𝑍𝑍𝑠𝑠 Γ𝑠𝑠 /Γ𝑒𝑒 in multi-scale turbulence simulations.