24P031-P
Effect of V-shaped target on recombining plasma
V 字ターゲットが再結合プラズマへ与える影響
Hiroyasu Komukai，Takaaki Iijima，Akira Tonegawa, Kazutaka Kawamura, Kounosuke Sato
小向広泰 飯島貴朗、利根川昭、河村和孝、佐藤浩之助

Department of Physics, School of Science, Tokai University,
1117 Kitakaname, Hiratsuka, Kanagawa, 259-1292, Japan
東海大学 理学部 物理学科 〒259-1292 神奈川県平塚市北金目 411

Eexperimental simulation of the divertor target configuration via detached plasma
formation of hydrogen sheet plasma have presented in a linear divertor plasma simulator
TPD-SheetIV. Two types of target geometry (V-shaped and oblique targets) have beeninvestigated. At the V-shaped target, detached condition with high radiation loss is
produced easily. The V-shaped target enhances the recycling and detachment plasma isattained there effectively. It can also be demonstrated preliminary by reducing heat flux
at small amount of gas puff flux and argon fraction.
.

1. Introduction

The divertor design for stable detachedplasma formation should be optimized to handle
such high heat and particle fluxes In the highperformance plasma for high power and longpulse operation. In JT-60SA or ITER, thebottom part of the divertor chamber forms a
distinct corner (V-shaped) with the target wasproposed for high gas conductance between thedivertor legs[1,2]. Recently, the closed Helical
Divertor (HD) in LHD is planned to accomplish
an active neutral particles control to improve
plasma confinement and to sustain highperformance
long
pulse
discharges[3].
Therefore, the divertor target geometry to becompatible with the high performance plasma is
one of key significant issues on detachedplasma.
Although there are a number of papers on thenumerical simulation of the target configuration,very little is known about the experimental
simulation of the V-shaped target on detachedplasma formation. The experimental simulationof both effects of the V-shaped target geometry
and impurity transport seeding with a noble gas
Ar on detached plasma formation of hydrogensheet plasma in a linear divertor plasma

simulator, TPD-SheetIV will be presented inthis report. In order to investigate the effect of
the target geometry, there are two possible
candidates for the target configuration. The
first one is a conventional oblique target due toreduction of the peak power load on the target.
The second one is V-shaped target with opposite
Discharge Region

Anode

Experimental Region
ProbeSheet Plasma

VUV spectroscopy

V-shaped target

Floating
Electrodes
Gas
Inlet

CathodeMagnetic
Coil

500 l/s
Pump

(a)

Gas
500 l/s Feeder
Pump

(b)

1500 l/s
Pump(c)

Schematic configuration of the linear
plasma simulator TPD-SheetIV and target
geometry (a)oblique, (b,c) V-shaped target.

Fig.1

A linerdivertor
simulator facility:
TPD-SheetIV has been built in the previouswork[4].
Figure 1 shows a schematicconfiguration of TPD-SheetIV and the target
configuration: (a) oblique target without theopposite plate= 30 degree), (b)V-shaped
target with the opposite plate (L = 45 mm,), and(c) V-shaped target with the opposite plate (L =90 mm) for accumulation of neutrals particles
near the target plate. Ten rectangular magnetic
coils formed a uniform magnetic field of 0.1 Tin the experimental region. The hydrogenplasma was generated at a hydrogen/deuteriumgas flow of 70 sccm with a discharge current of
30-100 A. The electron temperature andelectron density are measured with the plane
Langmuir probe located 3 cm in front of thetarget.

3. Experimental Results

Figure 2 shows the dependence of hydrogengas pressure P on the electron density ne and theelectron temperature Te at discharge current of
50 A in TPD-SheetIV. The geometry of thetarget plates are oblique target ( ■) andV-shaped target (▲:45mm), and V-shapedtarget(○:90mm). With increasing in P, thevalue of Te decreases gradually from 6 to 0.5 eV.
On the other hand, ne has the maximum value
and the maximum gas flow decreases withincreasing P. At V-shaped target, both ne andTe decrease at the lower pressure comparing
with oblique target. The Lyman Rydberg serieslines of neutral hydrogen were measured at anaxial distance, 3 cm in front of the target plate.
The brightness of the high-n Lyman series lines,
such as L and L, are directly related to therecombination rate of EIR. These high-nLyman series lines intensities can be used as anindicator of EIR.
4. Conclusions
We present the experimental simulation of thedivertor target configuration via detachedplasma formation of hydrogen sheet plasma in a6.0

obliqueV-shaped(45mm)
V-shaped(90mm)

4.0
2.00.0ne [1018 m-3]

2. Experimental apparatus

Te [eV]

plate for accumulation of neutrals particles near
the target plate.

2.5
2.0
1.5
1.0
0.5
0.0

0.0

0.1

0.2

0.3

0.4

contact gas flow (Pa m /s)
3

Fig. 1 Dependence of hydrogen contact gas
pressure P on the electron density ne at adischarge current of 50A. The geometry of
the target plates are oblique target (■),
V-shaped target( ▲ :45mm),and
V-shapedtarget(○:90mm).
linear divertor plasma simulator TPD-SheetIV.
Two types of target geometry (V-shaped andoblique targets) have been investigated. The
V-shaped target enhances the recycling anddetachment plasma is attained there effectively.
It can also be demonstrated preliminary byreducing Q at small amount of gas puff flux andargon fraction.
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Phys. Control. Fusion, 44 (2002)931.
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R.Schneider, V.Zhogolev, Nucl. Fusion, 42(2002)187.
[3]M.Shoji,M.Kobayashi,S.Masuzaki, .Watanabe,A.Iwamae,H.Yamada, A.Komori, andLHD Experimental Groups, Contrib. Plasma
Phys., 48 (2008) 185.
[4] A.Tonegawa,M.Ono,Y.Morihira, H.Ogawa,T.Shibuya,K.Kawamura,K.Takayama,
J.Nucl. Mater.,313-316 (2003) 1046.