24pE25P
仮想ダイバータモデルを用いた径方向プラズマ拡散の効果に関する非接触ダイバータプラズマのシミュレーション研究
Simulation Study of Detached Divertor Plasmas by Using a Virtual Divertor
Model Concerning the Effect of Radial Plasma Diffusion
東郷訓1, 滝塚知典2, 中村誠3, 星野一生3, 伊庭野健造2, ランティーロン1, 小川雄一1
TOGO Satoshi1, TAKIZUKA Tomonori2, NAKAMURA Makoto3, HOSHINO Kazuo3,
IBANO Kenzo2, LANG Tee Long1, OGAWA Yuichi1
東大新領域, 2阪大工, 3原子力機構
1
GSFS Univ. Tokyo, 2GSE Osaka Univ., 3JAEA
1Development of the control method of the detacheddivertor plasmas is crucial and the physicalmechanism of them is studied worldwide. In thesimulation studies, they often try to reproduce thebehavior of the ion saturation current measured inexperiments as a function of the midplane plasma
density. Simulation results, however, do notsatisfactorily agree with the experimental ones
especially for roll-over which means the reductionof the ion saturation current and is the sign of theonset of the detached divertor plasma [1].
As the candidates to reduce the ion saturation
currents, radial plasma diffusion is considered to beimportant in addition to the volume recombination.
Simulation studies of Particle-in-Cell (PIC) codewith binary collision model showed that supersonicflows can be driven by the strong gradient ofplasma density at the private region and indicatedthat smoother roll-over can be accomplished [2].
The effect of radial plasma diffusion on theroll-over was studied by using a code package [3].
In such code packages, however, flow velocities
cannot be self-consistently determined only by the
upstream conditions but the Mach number at thesheath entrance in front of the divertor plates isrequired to be given as a boundary condition.
In our simulation code, by introducing theanisotropic ion temperatures directly into theplasma fluid model, the parallel momentum
transport is described by the first-order differential
equation so that the flow velocities are determined
only by the upstream conditions [4]. In order tomodel the effects of divertor plate and sheath, weuse a virtual divertor model which sets an artificial
region beyond the sheath entrance with artificial
sinks of particle, momentum and energy [4].
We conducted simulations by setting parametersof medium-size tokamaks. We successfully
obtained supersonic flows in no-neutral conditions
which agree well with the results of PIC code [2]and the theoretical curves (Fig. 1). With neutrals,
we compared the behavior of the particle flux to thedivertor plates with radial plasma diffusion to thatwithout it in Fig. 2. By radial plasma diffusion, thehigh recycling regime appears which is observed inexperiments but supersonic flow does not appear. In
the presentation, we will discuss these results indetail including the effect of radial heat diffusion.

Fig.1

Mach numbers at the sheath entrance Mt (circles)
and X-point MX (squares). The dashed lines aretheoretical curves. The notation R is amplification
factor for the particle () and momentum (p)fluxes. The sum of parallel ion temperature andelectron temperature is denoted by T.

Fig.2

Particle flux amplification factor R as a functionof the particle flux from the core plasma sep
without (circles) and with (squares) the radialplasma diffusion.

[1] M. Wischmeier et al., J. Nucl. Mater. 390-391 (2009) 250.
[2] T. Takizuka et al., J. Nucl. Mater. 290-293 (2001) 753.
[3] K. Hoshino et al., J. Nucl. Mater. 463 (2015) 573.
[4] S. Togo et al., J. Nucl. Mater. 463 (2015) 502.