24P029-P
Improvement of edge-plasma modeling and its impact on
the SONIC simulation for JT-60SA divertor
周辺プラズマモデリングの改良と JT-60SA ダイバータの SONIC	 
シミュレーションにおけるその効果	 
Hisato Kawashima, Katsuhiro Shimizu, Kazuo Hoshino, Tomonori Takizuka and Shinji Sakurai
川島寿人, 清水勝宏，星野一生，滝塚知典、櫻井真治
Japan Atomic Energy Agency
801-1, Mukouyama, Naka 311-0193, Japan
日本原子力研究開発機構 〒311-0193	  那珂市向山 801-1
For SONIC simulation on JT-60SA divertor, the heat flux limiter is introduced in the ion parallel heattransport besides electron one. Changing the limit factor from αi = 0.5 to 10, density decrement andtemperature increment in the edge-plasma are remarkable at αi = 0.5 in comparison with a case without
limiter. Sensitivity on the radial particle or thermal diffusivity is surveyed with range of D = 0.1~1 m2/s
and χ = 0.1~2 m2/s. Divertor heat flux increases from 7.5 to 10.5 MW/m2 with decrease of D. Thissensitivity is stronger than that for χ.

1. Introduction
We have studied the JT-60SA [1] divertor
design with an integrated divertor simulation
code SONIC [2,3]. To identify compatibility thelow heat load (≤15 MW/m 2) with a maximum
input power Pin = 41 MW controlling the particle
flux, the vertical divertor targets with V-shaped
corner was adopted [4], and the gas-puff anddivertor pump were optimized [5]. Parametricsurvey of such as divertor geometry, gas-puff flux,
and pumping speed was carried out for theoptimization using the SONIC code. While, theflux limit with regard to parallel heat transport
was not included in the code. For particle andthermal diffusivity to the radial direction, fixedvalues were used. And the non-coronal model [6]was used restrictively for the impurity treatment.

In order to improve the modeling, the heat flux
limiter is introduced in the code and its effect isevaluated varying the factor of heat flux limiter.
Parametric studies varying the radial diffusivity arecarried out to clarify the effect to the edge plasma.
2. Parallel heat flux limit
The use of parallel heat flux limiter affects themodeling [7,8]. This is used in the codes totransition smoothly from collisional regime to a
kinetically limited term as the collisionality drops.
Simulations are carried out a condition for theJT-60SA operation scenario of full non-inductive
current drive (Rp=2.9 m, ap = 1.1 m, Ip = 2.3 MA, Bt= 1.8 T) with Pin = 41 MW. Figure 1 shows theeffects of changing the factor of ion heat flux limit
from αi = 0.5 to 10.0 (including a case without flux

Fig.1. Dependence on the ion flux limit factor αi of profiles of (a) electron density and (b) ion temperature profileon the outer midplane (ne-mid, Ti-mid), and (c) heat flux profile on the outer divertor target qtarget. Following
parameters on SONIC simulations are fixed. Total exhaust power and ion flux across r/a=0.95; Qtotal = 37 MW andΓion = 2.8×1021 s-1. Gas-puff flux; Γpuff = 6×1021 s-1. Pumping speed; Spump = 50 m3/s. Carbon and argon fraction;
nc/ni = 2% and nAr/ni = 1%. Particle and thermal diffusivity to the radial direction; D = 0.3 m2/s and χ = 1.0 m2/s.

limit) on profiles of electron density and ion
temperature in the outer midplane, and heat flux
profile on the outer divertor target. We are focusing
to the ion heat flux limit in this time. As shown inFigs. 1(a) and (b), lower density (separatrix density
ne-midsep = 0.8×1019 m-3) and higher temperature(separatrix temperature Ti-midsep = 1.4 keV) incomparison with a case without limiter (ne-midsep =1.8×1019 m-3, Ti-midsep = 0.4 keV) are exhibited at αi= 0.5 in the core edge regions. Its effect becomes
small rapidly with increase of αi. Then αi = 10.0
case is almost same as a case without flux limit. Onthe other hand, the target heat flux, which peakvalue is changed in range of qtargetpeak = 9~10.5
MW/m2 with change of αi, is not so affected by theflux limiter (Fig. 3(c)). It cannot make clear only bysimulation which factor is suitable, but it shows thatthe parallel heat transport can be changed withthose effects.
3. Sensitivity of particle or thermal diffusivity
The sensitivity of particle or thermal diffusivity
to the radial direction in the edge-plasma isevaluated with the range of D = 0.1~1.0 m2/s and χ= 0.1~2.0 m2/s based on the empirical values forvarious tokamaks [9]. Figure 2 shows thedependence on D of the midplane density profileand the target heat flux profile. The density profile
can be steepened with increment of separatrix
density from ne-midsep =1.4 to 1.8×1019 m-3 withdecrease of D. Heat flux profile on the target tends
to peak and peaked value becomes from 7.5 to 10.5
MW/m2 with decrease of D.
Dependence on χ of the electron temperature
profile on outer midplane Te-mid and the target heat
flux profile are shown in Fig. 3. Decreasing χ, theelectron temperature profile can also be steepened
and separatrix temperature is increased fromTe-midsep = 200 to 450 eV. Besides, ne-midsep also
increased from 1.4 to 1.8 ×1019 m-3 with decrease ofFig.2. Dependence on the particle diffusivity D of (a) ne-midand (b) qtarget.

Fig.3. Dependence on the thermal diffusivity χ of (a)electron temperature profile on the outer midplane Te-midand (b) qtarget.

χ. The target heat flux profile shifts outward withdecrease of χ (Fig.3 (b)), keeping qtargetpeak in rangesof 8.5~9.6 MW/m2. Resulting for the heat flux,
sensitivity of D is stronger than that of χ, and therange of D =0.1~1.0 m2/s gives a difference to theheat flux of Δq = 3 MW/m2
Those results indicate that a new modeling or
sensitivity of fixed parameters gives effects asmentioned above to the previous simulations andhas a possibility to improve the physics
understanding of the edge-plasma at the operation.
A similar thing is suggested for comparison ofdifferent model such as impurity treatment. Studyof impurity treatment using the Monte Carlo model
IMPMC [10] is in progress for comparison withthat on the conventional non-coronal model.
Acknowledgement
This work is partly supported by a Grant-in-Aidfor Scientific Research of Japan Society for thePromotion of Science.
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