22P133-P
Analysis of Core Plasma Fluctuation in Divertor Simulation Experiments onGAMMA10GAMMA10 におけるダイバーター模擬実験時のコアプラズマ揺動解析
Mizuguchi Masanori1, Sakamoto Mizuki1, Yoshikawa Masayuki1, Miyata Yoshiaki2,Aoyama Masato1, Furutachi Kenichi1, Akabane Yoshihiro1, Jitsukawa Katsuhiko1, Matsuyama
Shuhei1, Nakashima Yousuke1, Imai Tsuyoshi1
水口正紀、坂本瑞樹、吉川正志、宮田良明、青山真士、古舘謙一、赤羽泰央、実川克彦、松山周平、中嶋洋輔、今井剛
1. Plasma Research Center, University of Tsukuba,
1-1-1 Tennodai, Tsukuba, Ibaraki-ken 305-8571, Japan
2. Fusion Research and Development Directorate, Japan Atomic Energy Agency
801-1 Mukoyama, Naka, Ibaraki-ken 311-0193, Japan
1. 筑波大学プラズマ研究センター 〒305-8571 茨城県つくば市天王台 1-1-1
2. 日本原子力研究開発機構 核融合研究開発部門 〒311-0193 茨城県那珂市向山 801-1
Diverter simulation experiments have been performed in the GAMMA10 tandem mirror. The effect of theinsert of the divertor plate to the end region on plasma potential and its fluctuation at the core plasma isinvestigated by using a gold neutral beam probe. In the case of the plasma sustained by ICH and ECH,plasma potential increased when the diverter plate was inserted. The effect of the diverter plate on thepotential fluctuation is discussed.

1. Introduction
Recently, divertor simulation experiments havealso been performed by using a mirror end of thetandem mirror GAMMA10, where the plasma isinitiated by a plasma gun and sustained using ion
cyclotron heating (ICH) and electron cyclotron
heating (ECH) [1,2]. Plug-ECH and Barrier-ECH
produces positive and negative potentials at bothend mirrors for the axial confinement, respectively.
In this study, we investigate influence of thedivertor plate, which is inserted at the exit of theend mirror, on the core plasma. Potential and its
fluctuations of the core plasma at the central cellwere measured and analyzed by means of a gold
neutral beam probe (GNBP) [3,4].
2. Experimental device
GNBP is installed at the central cell ofGAMMA10. The gold neutral beam is injected tothe plasma and it is ionized in the plasma. The
ionized process is mainly electron impact ionization.
Therefore, the ionized beam current corresponds tothe electron density at the ionization point. Inaddition, the difference between the neutral andionized beam energy corresponds to the plasma
potential at the ionization point. The measurement
point was changed from R = 0 cm to R = 14 cm
shot by shot. The time and spatial resolutions are
estimated to be about 3 µs and 10 mm (i.e. a beam
diameter), respectively.

3. Experimental result
The divertor plate was inserted to the west mirror
end of GAMMA10. Initial plasma generated by aplasma gun was heated and sustained by ICH. Then,Barrier-ECH and Plug-ECH were applied to plasma
in the period of 160 ms to 190 ms and of 161 ms to
181 ms, respectively. Here, period in which theFig. 1. Line density and diamagnetic flux of the plasma

plasma is sustained by ICH only and by ICH andECH is called as “ICH period” and “ECH period”
respectively. It is noted that the initial plasma wasgenerated only by the east plasma gun in thisexperiment, since the divertor plate was inserted at
the west mirror end. Usually, both east and west
plasma guns were used. Time evolutions of line
density and diamagnetism are shown in Fig. 1(a)and (b), respectively. Red and Blue lines indicate
those without and with insertion of the divertor
plate, respectively. The line density increased due toapplying the Plug-ECH until it was switched off at t= 181 ms. On the other hand, the diamagnetism also
increased due to the Plug-ECH but it started todecrease during the Plug-ECH (around t = 170ms).
The behaviors of line density and diamagnetism
during the Plug-ECH seem to differ with each other.
Radial profiles of plasma potential at the central
cell are shown in Fig. 2. The profiles in Fig. 2
correspond to the time indicated by the arrows of A
and B in Fig. 1. The circle and the triangle in thefigure indicate the potential in the ICH period andthe ECH period, respectively. The yellow hatchingindicates the projected region of the divertor plate at
the central cell. When the divertor plate wasinserted to the west end, the potential increased in
the whole radial region of the plasma in the ECH
period. On the other hand, the potential did notchange in the ICH period even though the divertor
plate was inserted.

outer side, the fluctuation amplitude became higher
in the case of the insertion of the divertor plate.

Fig. 3. Radial profile of fluctuation amplitude

4. Summary
In the divertor simulation experiments ofGAMMA10, the plasma potential and its
fluctuations at the central cell are measured bymeans of GNBP. When the divertor plate is inserted
at the mirror end, plasma potential increased at thewhole radial region over the projected region of thedivertor plate in the period of the ECH period. The
characteristic fluctuation is not observed within thecentral area that is projected region of the divertorplate. In the outer side, characteristic fluctuation ofwhich frequency is 16-19 kHz can be observed.
References[1] Y. Nakashima, H. Takeda, R. Yonenaga, et al. Fus.
Sci. and Tec. 59, 1T (2011) 61-66[2] Y. Nakashima, M. Ichimura, I. Katanuma, et al. Fus.
Eng. and Des. 85, 6 (2010) 956-962[3] M. Yoshikawa, Y. Miyata, M. Mizuguchi, et al. Fus.
Sci. and Tec. 57, 4 (2010) 312-319[4] Y. Miyata, M. Yoshikawa, M. Mizuguchi, et al. Fus.
Sci. and Tec. 55, 2T (2009) 168-171Fig. 2. Radial profile of plasma potential. ICH and ECHtime in Figure indicated by the arrows of A andBin Fig. 1, respectively.

Figure 3 shows radial profile of low frequency
fluctuation amplitude in the latter half of the PlugECH period (i.e. t=170-180 ms). The characteristicfluctuation was 8 to 14 kHz for the case without thedivertor plate and 16 to 19 kHz for the case with thedivertor plate. In the case of the insertion of thedivertor plate, the signals were at the noise level,
and the characteristic fluctuation was not observed
around the central region. On the other hand, at the