24P025-P
Edge impurity transport study in the stochastic layer of LHD
LHDの周辺ストキャスティック層における不純物輸送の流体モデリングと実験観測の比較
Masahiro Kobayashi, Shigeru Morita, Chunfeng Dong, Suguru Masuzaki, Motoshi Goto, Yuehe
Feng* and the LHD experimental group
小林政弘, 森田繁，董春鳳, 増崎貴，後藤基志, Feng Yuehe*, LHD実験グループ
National Institute for Fusion Science, Toki 509-5292, Japan*Max-Planck-Institute fuer Plasmaphysik, D-17491 Greifswald, Germany
核融合科学研究所 〒509-5292 岐阜県土岐市下石町322-6*マックスプランク研究所 〒D-17491 ドイツ グライフスバルト
Edge impurity transport has been investigated in the stochastic layer of LHD based on thethree-dimensional (3D) edge transport code EMC3-EIRENE and on carbon emission profile measurement.
The carbon emission profile of CIV in the VUV range shows clear signature of C3+ movement towards
downstream at high density range. The transport simulation shows the strongest contribution of divertor
carbon source to the CIV profiles and shows reasonable agreement with the experiments, implying
screening effect. The newly installed visible spectrometer viewing divertor region shows clear difference inthe spectrum depending on the location from the divertor legs, stochastic region and the last closed flux
surface. The behavior is discussed in terms of the edge impurity transport.

1. Introduction
Understanding of edge impurity transport isone of the most critical issues in magneticallyconfined fusion devices. While the tokamak
X-point poloidal divertor is being optimized invarious aspects in the 2D (two-dimensional)
axi-symmetric geometry [1], the non-axisymmetrictokamaks [2] or helical devices [3,4] are exploring apossibility of the 3D (three-dimensional) magnetic
field geometry with toroidal symmetry breaking.
The 3D configuration usually introduces thestochasticity of magnetic field in the edge region,
where one expects substantial difference in thetransport properties compared to those in theaxi-symmetric tokamak scrape-off layer (SOL).
The previous works on the impurity transport
in the stochastic layer in various devices show thetendency of impurity screening [5]. But themechanism of the screening effect is not yet fully
understood. In this paper, we investigate theimpurity transport in the stochastic layer of LHD
edge region using the 3D edge fluid transport code,EMC3-EIRENE [6,7], and the VUV, EUV, visible
spectrometers.
2. 3D modelling results and spectrometermeasurements of carbon
EMC3-EIRENE solves the set of fluid equationsof particle, parallel momentum and energy, andprovides 3D distribution of plasma parameters andimpurity. The spectrometer viewing the LHD

plasma from the outboard side measures the line
integrated vertical profiles of emission fromplasmas. Figure 1 shows the measured profiles ofCIV for low (nLCFS=1.1x1019 m-3) and high(4.5x1019 m-3) density discharges. Z=0 mcorresponds to midplane and the figure shows theupper half profiles. It is seen that the profile
becomes peaked at the edge (Z~0.48 m) and aroundthe midplane with increasing density. Figure 2shows the vertical profiles obtained with themodelling using the same viewing chord as themeasurements. Since the detailed carbon source
distribution is not known, several cases are tested,
and the most probable profile is estimated withcertain proportion of the various sources, as shownin Fig.2 (e). The modelling shows that in the almost
all cases the profiles become peaked at themidplane and the edge. The results indicate theresultant impurity distribution is not very sensitive
to the source location. The change of the profiles isdue to the movement of C3+ carbon to thedownstream region at the high density, and they
populate around the X-point of the divertor legs andthe periphery of the stochastic layer. The emission
from the X-point is reflected as the increase of theCIV intensity around midplane, and the population
at the periphery leads to the peaks at the edge
(Z~0.48 m) due to the line integration effect. The
obtained profile, Fig.2 (e), reasonably agrees withthe experiments, suggesting impurity screening at
the high density discharges. The modelling showsstochastic region, up to LCFS, with increasing
channel numbers. The obtained spectrum from 220
to 525 nm are shown in Fig.4 before and after Ne
puff, for different channels. There appear clear
differences of the spectrum response depending on
the channels. The detailed analysis in terms of theimpurity transport is presented at the conference.

Experiments

1.5nLCFS=4.5x1019 m-3

1

1.1x1019 m-3

0.5
000.10.2 0.3Z (m)0.40.5Fig.1 Line integrated vertical profiles of CIV intensity
obtained with the VUV spectrometer.
3D modelling

5Chem. sput., 0.05eV divertor source

4ch1(a)ch5nLCFS=
5.0x1019 m-3

32

1.5x1019 m-3

1LCFS

05Chem. sput., 0.05eV wall source
4ch15(b)32ch201054
3
2105Phys. sput., 2eV divertor source

Fig.3 Viewing area of newly installed divertor
spectrometer.

(c)
105

Ch2 : divertor legs

Ch16 : LCFS

Before Ne puff
After Ne puff(d)4 Phys. sput., 2eV wall source

104321010 All sources

(e)

103
250 300 350 400 450 500
Wavelength (nm)50ch1000.1

0.2 0.3Z (m)0.40.5Fig.2 Line integrated vertical profiles of CIV intensity
obtained with the 3D modellings for different source
distribution.

that this screening is caused by the enhanced
friction force at high density, which pushes
impurity towards divertor region.
3. Experiments of Ne puff
In order to study the effect of impurity species on
the transport, Ne puff experiments are ongoing.
Figure 3 shows the viewing area of the newly
installed visible spectrometer looking at the divertor
region. The viewing chords are situated as it covers
the divertor legs near divertor plates through250 300 350 400 450 500
Wavelength (nm)Fig.4 Spectrum for Ne puff experiments at the different
channels. Black solid lines: before Ne puff, red brokenlines: after Ne puff.
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S203.
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[4] Grigull P. et al., Plasma Phys. Control. Fusion 43(2001) A175.
[5] Kobayashi M. et al., Fusion Sci. Technol. 58 (2010)
220.
[6] Feng Y. et al., Contrib. Plasma Phys. 44 (2004) 57.
[7] Reiter D. et al., Fusion Sci. Technol. 47 (2005) 172.