27D31P
ELMペーシングのためのペレット入射によるELMエネルギー損失の低減	 
Reduction of ELM Energy Loss by Pellet Injection for ELM Pacing
林	  伸彦1、相羽信行1、滝塚知典2、大山直幸1
N. Hayashi 1, N. Aiba 1, T. Takizuka 2, N. Oyama 1
1

原子力機構、2 阪大工
JAEA, 2 Osaka Univ.

1-WELM/Wped Wped

timing in the natural ELM cycle is found to besuitable for ELM pacing. With these suitableconditions, the ELM pacing with the reduced
energy loss is successfully demonstrated insimulations, in which the core density increase dueto additional particle fueling by the pacing pellet
can be compensated by reducing the gas puff andenhancing the divertor pumping.
1.20(a)

[MJ]

00.08

rp=0.6mm,
LFS
HFS pellet vp=120m/s
natural ELM

rp or vp variationtiming
A0CB(b)1-t/.cyc

FIG.1. (a) Wped without pellet and (b) ΔWELM
normalized by Wped as functions of Δt/τcyc. In (b),circles denote values of ELM triggered by a pellet
injected at each timing, shaded lines ranges forvarious pellet radius rp (≤0.7mm) and speed vp(5m/s≤vp≤120m/s), and triangles values of natural
ELMs.

0.08

"WELM/Wped

The energy loss caused by the edge localized
mode (ELM) needs to be reduced for ITER
operations with ELMy H-mode plasmas. The pellet
injection is considered as one possible method toreduce the ELM energy loss by increasing the ELM
frequency (so called ELM pacing). The ELM
pacing requires the significant reduction of ELM
energy loss, small impact on the plasma
performance, and less particle fueling. The
reduction of ELM energy loss by the pellet
injection for ELM pacing has been studied by an
integrated core / scrape-off-layer (SOL) / divertor
transport code TOPICS-IB with an MHD stability
code and a pellet model taking account of the ExB
drift of pellet plasma cloud [1].
The dependence of energy loss on the pellet
injection timing in one cycle of natural ELM withthe time period of τcyc is studied. Figure 1 shows (a)the time evolution of pedestal stored energy Wped
without the pellet and (b) the dependence ofnormalized ELM energy loss ΔWELM/Wped inducedby the pellet on the injection timing Δt/τcyc of both
high-magnetic-field-side (HFS) and low-field-side(LFS) pellet, where Δt is elapsed time fromprevious natural ELM. Early injection (A inFig.1(b)) reduces the energy loss because the highmagnetic shear prevents the onset of lower-n modes,
where n is the toroidal mode number, but leads to
the reduction of target pedestal pressure and theenlargement of pellet size to trigger the ELM. On
the other hand, the late injection (C) induces a large
energy loss comparable to the natural ELM.
Figure 2 shows the dependence of energy loss onthe pellet radius rp at the middle injection timing B.
The energy loss can be reduced by a small pellet
injected from LFS, which penetrates deeply into thepedestal and triggers high-n ballooning modes withlocalized eigenfunctions near the pedestal top. On
the other hand, a small pellet injected from HFS
triggers lower-n modes with wide eigenfunctions
before the pellet penetrates deeply into the pedestal,resulting in a large energy loss.
Therefore, the small pellet injected from LFS to
the pedestal plasma equivalent to that at the middle0

vp=120m/s

LFSHFS

natural ELMno trigger0rp [mm]0.8FIG.2. Dependence of ΔWELM on rp, where open
symbols denote pellets not to trigger ELM andhorizontal dotted line does ΔWELM of naturalELM.
[1] N. Hayashi et al, Nucl. Fusion 51 (2011) 103030.