23P086-P
ICRF Heating Experiments in the Minimum-B Anchor Configuration on GAMMA10GAMMA10 極小磁場アンカー部における ICRF 加熱実験
Takuro Yokoyama, Makoto Ichimura, Ryuya Ikezoe, Yumeto Ugajin, Toru Iwai, Tatsunori Sato
Takuma Iimura, Yu-ki Saito, Mafumi Hirata, Yuusuke Yamaguchi1, Atsushi Fukuyama2 and Tsuyoshi Imai
横山拓郎, 市村 真, 池添竜也, 宇賀神ゆめと, 岩井 透, 佐藤達典
飯村拓真, 齋藤裕希, 平田真史, 山口裕資 1, 福山 淳 2, 今井 剛
Plasma Research Center, University of Tsukuba, Tsukuba, Ibaraki, 305-8577, JAPANResearch Center for Development of Far-Infrared Region, University of Fukui, Fukui, Fukui, 910-8507, JAPAN 1
Department of Nuclear Engineering, Graduate School of Engineering, Kyoto University, Kyoto, 606-8501, JAPAN 2
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
福井大学 遠赤外領域研究開発センター 〒910-8507 福井市文京 3-9-1 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 2

On GAMMA10, ICRF waves produce and heat initial plasmas and keep MHD stability. MHD stability issupplied by the high-β plasma in the minimum-B configuration at the anchor cell. This plasma isformed by ICRF waves propagated from the central cell. Because these waves are also used for theproduction of initial plasma, it is difficult to change only the effect of the anchor heating. Then, anindependent system from the plasma production is needed for the anchor heating. In this study, we report
direct anchor heating experiments with antennas installed in the anchor cell.

1. Introduction
GAMMA10 is the largest tandem mirror device
in the world and consists of five magnetic mirror
configurations, which are a central cell, two anchor
cells connected to both sides of the central cell andtwo plug/burrier cells at both ends. The mainplasma is produced in the central cell withmagneto-hydrodynamic (MHD) stability attainedby the high-β plasma in the anchor cells withminimum-B configuration. The anchor plasma isheated by Ion-Cyclotron Range of Frequency(ICRF) waves (around 10MHz). In the standard
discharge, ICRF waves which have resonancelayers near the anchor midplane are excited in thecentral cell and propagate to the anchor cell. Since
these waves are also used for the plasma productionin the central cell, it is difficult to control only theheating effects in the anchor cell. In order toenhance anchor heating, an antenna is installed inthe anchor cell. In this study, we replaced theanchor antenna so as to improve its coupling withthe facing plasma and confirmed its validity by theexperiment and the computer simulation.
2. Experimental setup
Figure 1 shows the schematic drawing ofmagnetic field configuration and ICRF systems on

GAMMA10. There are three ICRF systems, which
are RF1 with the Type-Ⅲ antennas for producing
initial plasma and heating anchor plasma, RF2 with
Double Half Turn (DHT) antennas for heating mainplasma in the central cell and RF3 with the anchor
antenna for heating anchor plasma.

Fig.1. GAMMA10 tamdem mirror device

The anchor heating experiments have beenproceeded by using two types of antenna. Figure 2
shows (a) a bar-type antenna, which has been usedpreviously, and (b) a new type antenna, which has
double elliptic arcs so as to surround the facing
plasma. The experiment with the bar-type antenna

has been performed and the stabilization of thewhole plasma has been confirmed[1]. The loading
resistance of the bar-type antenna and the newantenna are calculated by a three-dimensional fullwave numerical code, which is developed by one of
the authors (A. Fukuyama).

(a)Bar-type antenna

modification of the antenna shape from simple
bar-type to the double elliptic arcs type.

(b)New antenna

Fig. 2. Schematic drawing of two type antennas

This code solves the Maxwell's equation for thewave electric-field as a boundary-value problem
using the finite element method. The model
assumes that cold and inhomogeneous plasma issurrounded by a conducting wall. The power
absorption with the collisional damping is describedby introducing effective collisions in the dielectric
tensor. According to the result of this calculation,
the loading of the bar-type antenna has been foundto be very small and that of the new antenna is threetimes larger than that of the bar-type antenna.
3. Experimental results
We have performed anchor heating experiments
using two types of anchor antenna. The results areshown in Fig. 3. In these experiments, ICRF wavesof 9.7MHz are used. The diamagnetism and theline-integrated density in the central cell are shownon top graphs of Figs.3 (a) and (b). The input andnet powers of RF3 with the anchor antenna areshown on bottom graphs of them. These effects on
the diamagnetism and the line-integrated density inthe central cell are larger in case of using the newantenna than the bar-type antenna. This is partly
due to the difference of the radiated power to theplasma. In the case of the bar-type antenna,
although the input power is about 130kW, only
one-sixth of power is radiated to the plasma. In
other words, less than five-sixth of the power isused on the circuit including the antenna, whichindicate weak coupling to the plasma. On thecontrary, in the case of the new antenna, more
power is radiated from the antenna although theinput power is much less than that in the case of thebar-type antenna. From this result, we confirmedthat antenna loading is clearly improved with theFig. 3. Temporal evolution of plasma parameters byapplying RF3 with (a) the bar-type
and (b) the new antenna

4. Summary
In order to heat plasma effectively in the anchorcell, the bar-type antenna was replaced to the new
designed antenna. In the experiment, we haveconfirmed that the plasma in the central cell isaffected more effectively by ICRF waves from thenew antenna than the bar-type antenna, whichreflects the improvement of antenna loading.
Acknowledgments
This work is partly supported by thebidirectional collaborative research program ofNational Institute for Fusion Science, Japan(NIFS11KUGM055).
Reference[1]Y.Yamaguchi et al., Fusion Science andTechnology, 59, No.1T(2011)250-252.