27E11P
固定熱流および固定勾配駆動ITG乱流の大域的ジャイロ運動論シミュレーション	 

Fixed-flux and fixed-gradient global gyrokinetic simulations of ITG turbulence
仲田 資季, 井戸村 泰宏
Motoki NAKATA, Yasuhiro IDOMURA
日本原子力研究開発機構
Japan Atomic Energy Agency
In this study, systematic comparisons among
several gyrokinetic simulation models, i.e., a global
full-f fixed-flux(FF), a global delta-f fixedgradient(FG), and a local fluxtube(FT) models,
have been carried out by using a full-f Eulerian
gyrokinetic code GT5D[1, 2] and a local fluxtube
code GKV[3], and then, plasma-size(ρ*) andcollisionality(ν*) dependences of ion temperature
gradient(ITG) turbulent transport have been
investigated. In order to emulate a delta-f
simulation in GT5D, a FG source model are newly
implemented by extending an adaptive momentum
source model in Ref. [4]. It is emphasized that in
the FG model, artificial source and sink inside
the plasma compensate local temperature
variations, and they account for ~85% of thetotal power balance.
The ν*-dependence on turbulent transport at
far above marginal states are verified through theinter-model comparison. The weak ν*- dependenceof the heat diffusivity, which has also been
observed in L-mode discharges[5], has been
confirmed in the FF and FT models. In the FG
simulations, converged results are obtained for ν*≤ 0.0143 that is regarded as an asymptotic
collisionless limit[6], while the transportenhancement in proportion to ν* is observed above
this threshold. The detailed analysis has highlighted
a problematic behavior of the conventional FG
source model in the high ν*- regime, where theprofile relaxation towards the collisional
equilibrium may cause a spurious heating as ν*increases.
The ρ*-scan with the FF simulations isextended towards the local limit regime(ρ*-1>300),
where the heating power is simultaneously scaledwith the plasma size(cf. Ref. [4, 7]). The Bohm likeheat transport associated with the formation of stiff
temperature(Ti) gradient profiles bounded by near
critical value R0/LTi~6.5 has been found even in thelocal limit regime, where the profile shear effects
become significantly weak[see. Fig. 1]. Small-scaleavalanches bounded by the radial scale of zonal
flows and the large bursty behavior, which
propagates over significant radii across zonal flows,

are identified. It has been clarified that despite thestiff-Ti profiles with similar mean-R0/LTi (FT results
give only ~7% difference in the heat diffusivity),
local variations of power balance before bursts can
produce significantly different super-critical statesof R0/LTi leading to the Bohm like burst amplitudein the heat diffusivity.
Close comparisons of the statistical properties(PDF, frequency spectra) and zonal flows among
FF, FG, and FT models have shown many
similarities, but it is emphasized that thelocal power balance dynamics, which is important
for the Bohm like heat transport and the profile
stiffness, is essentially different among thesemodels.

Fig. 1 Bohm like ρ*-scaling of the heat diffusivity
in the FF simulation, where Pin denotes the heatingpower. The shaded region shows the transport levelobtained from FT simulations for stiff Ti-gradientparameters R0/LTi=6.20(ρ*-1=300), 6.55(ρ*-1=450).
References[1] Y. Idomura et al., Comput. Phys. Comm 179, 391(2008)[2] Y. Idomura et al., Nucl. Fusion 49, 065029 (2009)[3] T. -H. Watanabe et al., Nucl. Fusion 46, 24 (2006)[4] S. Jolliet et al., Nucl. Fusion 52, 023026 (2012)[5] C. C. Petty et al., Phys. Plasmas 6, 909 (1999)[6] T. -H. Watanabe et al., Phys. Plasmas 11, 1476(2004)[7] C. C. Petty et al., Phys. Plasmas 2, 2342 (1995)