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

Comparison of Collisional and Turbulent Energy Exchanges
between Ions and Electrons in Tokamak Plasmas
T. Kato1, H. Sugama1, 2, T.-H. Watanabe3 and M. Nunami2, 3
1Graduate School of Frontier Science, The University of Tokyo, 2 National Institute for Fusion
Science, 3 Graduate School of Science, Nagoya University
e-mail (speaker): kato.tetsuji21@ae.k.u-tokyo.ac.jp
In magnetically confined plasmas, turbulence induces
particle and heat fluxes, and also causes energy exchange
between electrons and ions [1, 2]. In a previous study [3],the effect of turbulent energy exchange on prediction ofplasma density and temperature profiles was investigatedunder specific conditions and it was found to be negligible.
However, the paper [3] did not make a detailed
comparison between the turbulent and collisional energy
exchanges in the case of very high-temperature plasmas
such as those in ITER, where the collision frequency isvery low.
In this work, effects of ion temperature gradient (ITG)
turbulence on the energy exchange between electrons andions in tokamak plasmas are quantitatively investigated bygyrokinetic simulations and their dependence on plasma
conditions such as collision frequency and the electron-toion temperature ratio is clarified. In addition, the ratio of
turbulent and collisional energy exchanges is evaluated,
and a wavenumber space spectral analysis is performed toelucidate the mechanism of the turbulent energy exchange.
We use the gyrokinetic simulation code GKV[4] andfocus on the ITG turbulence under the Cyclone DIII-D
Base Case plasma conditions [5]. Here, kinetic electrons
are considered, and the electron temperature gradient isassumed to be zero. The ion beta 𝛽! = 1 × 10"# is used
and the ratio of the electron and ion temperature is varied
from 𝑇$ /𝑇! = 0.8 to 1.5.
There are different properties between collisional andturbulent energy exchanges. As the plasma temperature isincreased, the collisional energy exchange decreases andthe turbulent energy exchange increases. Therefore,

turbulent effects dominate the energy exchange at hightemperature (low collision frequencies). Also, thedirection of energy exchange is clearly different when
𝑇$ / 𝑇! > 1. Figure 1 shows the turbulent and collisionalenergy exchange as functions of the temperature ratio
𝑇$ / 𝑇! . Here, 𝑄!%&'' and 𝑄!()*+ are defined as thecollisional and turbulent energy transfers from electrons
to ions, respectively. Coulomb collisions make energy
transfer from hotter to colder species. However, in the ITG
turbulence, energy can flow from colder ions to hotter
electrons. Figure 1 shows that, even for 𝑇$ > 𝑇! , the net
energy can flow from low temperature ions to hightemperature electrons. Furthermore, in isothermal plasma
conditions, the collisional energy exchange vanishes
while the turbulent one doesn't.
In addition, we investigate the physical mechanism ofturbulent energy exchange in ITG turbulence and thecorrelation between the results of linear and nonlinear
calculations.
References[1] H. Sugama, M. Okamoto, W. Horton and M.
Wakatani, Phys. Plasmas 3, 6, 1996.
[2] H. Sugama, T.-H. Watanabe, and M. Nunami, Phys.
Plasma 16, 112503, 2009.
[3] J. Candy, Phys. Plasmas, 20, 082503, 2013.
[4] T.-H. Watanabe and H. Sugama, Nucl. Fusion 46, 24,2006.
[5] A. M. Dimits et al., Phys. Plasma 7, 969, 2000.

Figure 1. The collisional and turbulent energy transfers, 𝑄!%&'' and 𝑄!()*+ , from electrons to ions are plotted asfunctions of the electron-to-ion temperature ratio 𝑇$ / 𝑇! (𝑇! = 3.0 keV, 𝑛$ = 𝑛! = 1 × 10,- m". , 𝐵 = 2.2 T ).
When 𝑇$ / 𝑇! > 1, turbulent energy exchange exhibits a larger magnitude and an opposite direction compared tocollisional energy exchange.