03aE55P
閉じ込め時間スケールのfull-fジャイロ運動論シミュレーション	 Full-f gyrokinetic simulation over a confinement time
井戸村	  泰宏
Yasuhiro IDOMURA
原子力機構
JAEA
In recent years, new generation of gyrokinetic
simulations based on the so-called full-f approaches
are emerging. In full-f gyrokinetic simulations, both
turbulent transport and profile formations arecomputed under fixed power, momentum, andparticle inputs as in the experiment. This approach,in principle, has the capability of dictating plasma
profiles, provided that the simulation is performed
over a confinement time. In fact, recent Peta-scale
supercomputers made such long time scale
simulations feasible. However, before proceeding tosuch a huge computation, one needs to examine theaccuracy of physical and numerical models. In
particular, recent work [Parra, POP2011] pointed
out a serious concern about the accuracy ofmomentum transport calculations using standard 1storder gyrokinetics.
In order to resolve this critical issue, we have
implemented 3rd order gyrokinetics [Mishchenko,POP2011] to the Gyrokinetic Toroidal 5D Euleriancode GT5D [Idomura, CPC2008, NF2009], and thequantitative convergence of turbulent momentum
transport is examined in the ion temperature
gradient driven (ITG) turbulence [Idomura,CSD2012]. The result shows that both heat andmomentum fluxes are well converged even with 1storder gyrokinetics. It is found that in the ITG
turbulence with k⊥ρi<1, higher order corrections to
the ion polarization density are negligibly small,and that non-diffusive momentum transport due toresidual stress and related intrinsic rotation are anorder of magnitude larger than those assumed in the10

9730.1

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0.08

871

U||/vti5
t=0s
t=0.002-0.005s
t=0.005-0.008s
t=0.008-0.011s
t=0.011-0.014s
t=0.014-0.017s

32

6900.0050.01
time (s)

0.015

1

t=0s
t=0.002-0.005s
t=0.005-0.008s
t=0.008-0.011s
t=0.011-0.014s
t=0.014-0.017s

0.04

6470

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0.06

772
R/Lti

ion stored energy (kJ)74

so-called low flow ordering. These corrections tothe conventional ordering arguments lead to theconvergence of momentum transport.
After verifying the accuracy issue, long time ITGturbulence simulations are performed for a normal
shear tokamak with ρ*-1~100, Pin=4MW, and no
momentum input. In the simulation, the quantitative
convergence of steady temperature and (intrinsic)
rotation profiles is confirmed after an energy
confinement time, while profiles after a collisiontime are rather close to them. It is shown that theprofile relaxation can be significantly accelerated
when the simulation is initialized with linearly
unstable temperature profiles. In the steady state,
the temperature profile and the ion heat diffusivity
are self-consistently determined by the power
balance condition, while without momentum input,
the intrinsic rotation profile is sustained bycomplicated momentum transport processes. Thesteadyturbulent
momentumtransport
ischaracterized by bursty non-diffusive fluxes, andthe resulting turbulent residual stress is consistent
with the profile shear stress theory [Camenen,NF2011], in which the residual stress depends not
only on the profile shear and the radial electric field
shear but also on the radial electric field itself.
Based on the toroidal angular momentum
conservation, it is found that in the steady null
momentum transport state, the turbulent residual
stress is cancelled by the neoclassical counterpart,which is greatly enhanced in the presence ofturbulent fluctuations.

0.2

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r/a0.60.8

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0-0.02
-0.04
-0.06
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r/a

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Fig.1: Long time ITG turbulence simulation. Time evolutions of (a) plasma stored energy, (b) temperature gradientprofiles, and (c) parallel flow profiles. Profiles after a collision time (∼3ms) are qualitatively similar to converged ones.