23P092-P
Heating experiment with phase-controlled antennas on GAMMA10GAMMA10における位相制御アンテナによる加熱実験
Yumeto Ugajin, Makoto Ichimura, Yokoyama Takuro and Tsuyoshi Imai et al
宇賀神ゆめと, 市村 真，平田 真史, 池添 竜也, 横山 拓郎, 岩井 透,佐藤 達典, 飯村 拓真, 齋藤 裕希, 福山 淳1, 吉川 正志, 南 龍太郎 今井 剛，Plasmas Research Center, University of Tsukuba
1-1-1, Tennodai, Tsukuba-shi, Ibaraki 305-8577, Japan
Department of Nuclear Engineering, Gratuate school ofEngneering, Kyoto University
Yoshidahonmachi, Sakyo-ku, Kyoto-shi 606-8501, Japan1
筑波大学プラズマ研究センター 〒305-8577 茨城県つくば市天王台1-1-1
京都大学工学研究科原子力工学専攻 〒606-8501 京都市左京区吉田本町1
Production of high β plasmas in anchor-cell is necessary for MHD stabilization in the tandem mirror
GAMMA10. Plasma heating in anchor-cell has been carried out by ICRF system(RF1) with both east andwest type-Ⅲ antennas installed in the central-cell. By using an additional ICRF system (RF3) with abar-type antenna installed in the east anchor-cell, more effective anchor heating have been confirmed. Easttype-Ⅲ and the bar-type antennas are driven with the same frequency and phase difference between twoantennas can be controlled in the experiment. Plasma parameters depend on the phase difference between
both antennas. Increase of the line density and the soft X-ray signal are observed in the opposite phase.
Stable plasma production with only east RF1 and east RF3 is also confirmed.

1. Introduction
By producing high β plasmas in the anchor-cell
we can control MHD stability on the tandem mirror
GAMMA10. It is planned to modify the west
anchor-cell to the axisymmetric mirror field with adiverter configuration in near future [1]. Higher βplasma production in the east anchor-cell is needed
to keep MHD stabilization of whole plasmas inGAMMA10. By using phase-controlled antennas,
we have tried effective plasma heating in theanchor-cell.
2. Experimental Set-up
Figure 1 shows the schematic drawing of theGAMMA10 tandem mirror. Central-cell is a main
plasma confinement region. Anchor-cell has aminimum-B field and keeps MHD stabilization.
Plasma production and heating are mainly carriedout by ICRF waves on GAMMA10. There are 3 RFsystems; RF1, RF2 and RF3. Locations of ICRF
antennas are indicated in Fig. 1. RF1 with type-Ⅲ
antennas installed in the central-cell produces
plasmas and heats ions in the anchor-cell. RF2
system with double half turn antennas installed in
the central-cell heats ions in the central-cell. In the
typical discharge, anchor heating is carried out by
only RF1, of which frequencies are 9.9MHz (East)and 10.3MHz (West), respectively. In this study,
RF3 is used for the anchor heating with the same
frequency as East RF1 of 9.9MHz by using thesame signal-generator (SG). By using phase-shifter(PS), phase differences between two antennas arecontrolled.
Waves exited with same frequency interferewith each other. Then wave propagations areaffected from the phase difference. Anchor
resonance layer exists in the east side of RF3antenna. Powers propagating to the east side of bothantennas, PE, and to the west side, PW, are expressed
as follows:

Here, P0 is the power when only one antenna isexited. kz is parallel wave number determined witha dispersion relation. d is the axial distance between
two antennas. is the phase difference between twoFig.1. schematic drawing of the GAMMA10

antennas. Standing wave is formed between twoantennas. Wave propagations can be estimated byusing antenna loading resistances. Main diagnostic
systems used in this study are diamagnetic loops formeasuringplasmapressure,
microwave
interferometers for measuring electron line density
and soft X-ray detector for the information of theelectron temperature.
3. Experimental Result
Firstly, RF3 is superposed to typical discharges
and dependence of the phase difference on plasma
parameters is measured. Secondly, the plasma
sustainment with only east RF1 and RF3 is tried.
3.1 Phase control experiment
Figure 2 shows temporal evolution of electronline density. RF3 is superposed on typicaldischarges from 120msec to 240msec and the phasedifferences between both east RF1 and RF3 arechanged. When phase difference is 0.23radian,electron line density rise from 4×1013cm-2 to
6×1013cm -2 during RF3 pulse. The electron
density in the core region increases and the radial
profile is almost same as the case without RF3. On
the other hand, when phase difference is-2.76radian, electron line integral density seems nochange from typical plasmas. Figure 3 shows
temporal evolution of soft X-ray signal. Whenphase difference is 0.23radian, soft X-ray signal
decrease during RF3 pulse. On the other hand, soft
X-ray signal increases nearly 3times that before

RF3 pulse, when phase difference is -2.76radian.
According to measurement of Thomson scatteringsystem, electron temperature increases from 34eV
to 70eV on this phase difference. These indicatethat plasma parameters vary depending on phasedifference. According to measurement of theantenna loading resistances, wave propagation isestimated as follows. When phase difference is0.23radian, wave propagates toward east-side of
RF3 antenna and west-side of east RF1 antenna. On
the other hand, standing wave is formed between
two antennas, when phase difference is -2.76radian.
3.2 Experiment with only east RF1 and east RF3
As a simulation of the operation without west
anchor cell experiments with only east RF1 andRF3 are carried out. By controlling the phasedifference between both antennas, we haveachieved the production of the stable plasmas asshown in Fig. 4. Electron line density reaches to
4×1013cm-2 and diamagnetism reaches to 6×10-5Wb.
They are almost same as plasma parameters oftypical discharges on GAMMA10.

Fig.4. W/O west RF1 experiment4.

Fig.2. Time development of line density

Summary
By using RF3 with the same frequency as theeast RF1, we found following results. On the
typical plasmas when wave propagates toward
east-side of RF3 antennas and west-side of RF1
antennas, electron density rise and when standing
wave is formed between two antennas, electron
temperature rises. Even if only east RF1 and RF3
was used we can produce same plasmas as typicalone by optimizing phase difference.
Acknowledgments
This work is partly supported by the bidirectional
collaborative research program of National Institutefor Fusion Science, Japan (NIFS11KUGM055).
References[1] Y. Nakashima, et al: Fusion Sci. Technol. 59 (2011)61-66.

Fig.3. Time development of SX signal