23P144-B
Eﬀect of V-shaped target plate on the neutral particle behavior
中性粒子挙動に及ぼす V 字ターゲット形状の効果
Hiroto Matsuura,Hiroyasu Komukai,Akira Tonegawa,Suguru Masuzaki
松浦 寛人, 小向広泰, 利根川昭, 増崎貴Res. Org. for Univ.-Comm. Collabo., Osaka Pref. U.,
Gakuen-cho 1-2, Naka-ku, Sakai, Osaka 599-8570, Japan
大阪府立大学地域連携研究機構、〒 599-8570 大阪府堺市中区学園町 1-2
Experiment on eﬀect of V-shaped target plate on the plasma detachment is done with divertor
simulator TPD–SheetIV. The neutral behavior under this experiments is studied with DEGAS2 simulation code. In this work, new mesh models constructed to simulate more realistic
experimental situation and comparison of various simulation results makes the basic behaviorof neutrals more clear.

1. Introduction
In fusion reactors such as the International
Tokamak Experimental Reactor (ITER), tremendous heat ﬂux (> 10 [MW/m2 ]) is expected toﬂow onto divertor target plates. The development of for reducing the heat ﬂux on the divertor plate is an important challenge for thefuture fusion reactor design. One of the mostpromising methods is to establish a so-called
detached plasma, whose electron temperature
is kept below 1 [eV] by powerful cooling due
Fig.1: Schematic drawing of V-shaped target
to gas puﬃng. The most recent proposal is toplate of TPDSheet–IV.
use a so-called V–shaped target plate, which is
expected to increase the local neutral densityand enhance the volume recombination process.
Experimental study of a V–shaped target
in the linear divertor plasma simulator, Test
Plasma produced by Directed current device
for sheet plasma (TPD–SheetIV), has been
conducted[1].The V–shaped target enhances
recycling, and plasma detachment is eﬀectively
achieved in that device. Under such conditions, neutral particles are expected to experience not only transport but also atomic/ molecular processes such as dissociation and ionization. Their behavior has been experimentallystudied mainly with H-alpha monitors. However, because of a limited number of ports andchannels in the experimental devices, an iterative simulation to determine such parameters is indispensable. Although ﬁrst simulaFig.2: Simulation mesh model for V-shapedtion results for TPD–SheetIV with DEGAS 2target, which was improved from those used
code [2] are reported in [3], the mesh model isfor Fig.3 in [3].
improved and the eﬀect of target geometry is
studied farther in this work.

2. DEGAS 2 simulation modelH2_pressure_in_DEGAS2
Figure 1 shows the sheet plasma and tar(MAX=0.5E+0[mTorr])get plate of the TPD–SheetIV experiment. A
steady state plasma is produced by a TPD–
18[cm]
type dc discharge, and forms a sheet shapewith the thickness of only 3 ∼ 10 [mm]. Gas
feeder provides additional neutral gas and plasma
detachment is induced with it.
Simulation model used in [3] had some difference with the real TPD–SheetIV. That is1) the direction of inclined plate, 2) relative
position of gas feeder, 3) artiﬁcial minor modiﬁcation of recycling source. The third diﬀerence was due to minor bug of the code, and is
ﬁxed in the latest version source [4]. Figure 20015[cm]shows the improved version of V-shaped target model used in [3]. The plasma parameters
Fig.3: Hydrogen molecular pressure result
used in this work are those for the attachedwith the old inclined target mesh model.
condition, since the eﬀect of the target shapeon heat load is found to be maximum for small
additional gas feed.
0.00 E 0

H2_pressure_in_DEGAS2(MAX=0.5E+2[mTorr])

3. Simulation result

0.00 E 0

Firstly the eﬀect of direction of inclined
plate is studied. The neutral gas pressure
simulated with old mesh model used in [3] isshown in Fig. 3. In this model, target platefaces directly the gas feeder. Hence gas pressure near the plate is relatively high. On thecontrary, for new mesh model (Fig. 4), neutral
particles from gas feeder is blocked to reachthe plate surface by the support structure.
The particle number feeded through the gas
feeder in these simulation is set to be equalth those plasma ion recycling. So recycling
neutral eﬀect seems also to be clear. But weassumed that these neutral is reﬂected only
as high energy Hydrogen atoms and lost fromthe recycling area soon.
Other eﬀect of target geometry will be presented at the conference site.
Acknowledgements
One of the authors (H.M.) acknowledges Dr.
D. Stotler (PPPL), H. Takenaga (JAEA) and
B.J. Xiao (ASIPP) for the their advice on DEGAS 2 simulation. This work is performed inpart under the auspices of the NIFS Collaborative Research Program (NIFS08KOAP021/NIFS10KNXN191).

0.50 E 0

5.00 E 1

18[cm]

0015[cm]Fig.4: Hydrogen molecular pressure resultwith the old inclined target mesh model.

References[1]

A.Tonegawa et al., 19th TOKI conference ( Toki,2009) 2P-56.

[2]

D.P.Stotler et al., Contrib. Plasma Phys. 34, 392(1994).

[3]

H. Matsuura, et al., Plasma Fusion Res. 6,
2401104(2011).

[4]

D.P.Stotler, private communication.