23P091-P
ECH Power Modulation Experiments in GAMMA 10 Tandem Mirror
GAMMA 10におけるECHパワー変調によるプラズマ制御実験
Ryutaro Minami, Tsuyoshi Kariya, Tsuyoshi Imai, Tomoharu Numakura, Yoichi Endo,Hitomi Aoki, Hideaki Iizumi, Hidetaka Nakabayashi, Taku Eguchi, Ryo Kawarasaki,
Kazuhiro Nakazawa, Mizuki Sakamoto, Masayuki Yoshikawa, Junko Kohagura,
Yousuke Nakashima, Makoto Ichimura, Mafumi Hirata, Ryuya Ikezoe and GAMMA 10 Group
南 龍太郎，假家 強，今井 剛，沼倉友晴，遠藤洋一，青木 瞳，飯泉英昭，中林英隆，
江口 濯，河原崎遼，中澤和寛，坂本瑞樹，吉川正志，小波蔵純子，中嶋洋輔，市村 真，平田真史，池添竜也，GAMMA 10グループ
Plasma Research Center, University of Tsukuba
1-1-1 Tennohdai, Tsukuba 305-8577, Japan筑波大学プラズマ研究センター 〒305-8577 つくば市天王台1-1-1
Electron cyclotron heating (ECH) power modulation experiments in GAMMA 10 have been started inorder to generate and control the high heat flux and to make the ELM (edge localized mode) likeintermittent heat load pattern for divertor simulation studies. ECH for potential formation at plug region(P-ECH) produces electron flow with high energy along the magnetic filed line. Heat flux during ECH
injection corresponds to the steady-state heat load of the divertor plate of ITER. In this paper, thepreliminary experimental results in P-ECH power modulation are reported.

1. Introduction
Electron cyclotron heating (ECH) is apromising way to heat magnetically confinedplasmas. Besides the plasma heating, ECH has
been recognized as a useful tool for plasma
production, current drive, plasma profile
modification, magnetohydrodynamics control,
and transport study. Particularly, in the GAMMA
10 tandem mirror, ECH is recognized as a
primary scheme to produce plasma-confining
potentials.
In the GAMMA 10, fundamental ECH at theplug region (P-ECH) generates the axial ion
confining potential φc. Experimental observationshows that φc increases with the P-ECH power,
and no saturation has thus far been observed aslong as the electron density is kept at a certain
level. The P-ECH drives a portion of the heatedelectrons into the loss cone and induces anintense axial flow of warm electrons. A portion ofthe axially flowing electrons is observed as endloss electrons.
The new program to simulate the divertor
plasma which utilizes the mirror advantages havebeen started, in addition to the core confinement
studies as the mainframe 6 year work plan[1].
The peak heat-flux of 9 MW/m 2 was obtained
during the ECH injection. It continues to increase
with ECH power and is expected to be achieved
more than 10 MW/m 2 within the available powerof ECH (≤450 kW). This value almost

corresponds to the steady-state heat load of thedivertor plate of ITER. The ECH power
modulation is expected to enhance and control thehigh heat flux and to simulate the ELM likeintermittent heat load patterns, though we need
substantial upgrade of the heating power toapproach the ITER level ELM energy density.
In this paper, the first experimental results in
P-ECH power modulation are reported.
2. Experimental apparatus
The GAMMA 10 is the world largest tandem
mirror device (full length of 27 m), featuring theMW level high power heating systems. The plasma
confinement is achieved by a magnetic mirror
configuration as well as positive and negative
potentials at the plug/barrier region formed by ECH.
The main plasma confined in the central cell of
GAMMA 10 is produced by ion cyclotron range of
frequency (ICRF) wave. Figure 1 shows the axial
magnetic field intensity and locations of the heatingsystems used in the preliminary P-ECH modulation
experiment.

Fig.1. Axial magnetic field intensity and locations ofheating systems for P-ECH modulation
experiment.

3. Experimental results
Experiment for ECH power modulation in theeast plug region is carried out by the use of aplasma discharge after the time of t=150 ms (Fig.
2).

Fig.2. Temporal evolution of end loss electron
current at the (a) east end, (b) west end, andend loss ion current at the (c) east end, (d)west end. The P-ECH power of about 200 kW
is applied from t =150 ms to 180 ms with
100%, 100 Hz square wave power modulation.

During ECH from t =150 ms to 180 ms, the pulseof ECH power of about 200 kW is applied threetimes by 100%, 100 Hz square wave power
modulation [between dot-lines in Fig. 2]. The end
loss electron current at the west end is increased
during ECH injection [Fig. 2(b)], while the end loss
electron current at east end is not so increased
during ECH injection [Fig. 2(a)]. The end loss
current is measured with a multi-gridded
electrostatic energy spectrometer. The pulse train of

the electron current is due to sweep of the repeller
voltage for energy analysis. Its envelope represents
the electron current.
In Fig. 2, the end loss ion current at the west end
is a little increased during ECH injection [Fig. 2(d)],while the end loss ion current at east end isdecreased during ECH injection [Fig. 2(c)]. Also its
envelope represents the ion current.
The P-ECH has two functions on electrons bydriving two types of velocity space diffusion. The
first type of diffusion enhances mirror reflection
beyond the plug position, which results in the plugpotential. When ECH is applied only to the east
plug region, the end loss ion current at the east end
decreases owing to the potential reflection of low
energy ions [Fig. 2(c)], while the end loss ion
current at the west end increases owing to the ionsreflected by the east plug potential [Fig. 2(d)]. The
second type of diffusion creates the electron flow
[Fig. 2(b)]. These data indicate that the P-ECH isable to control the end loss ion and electron fluxes
by the use of power modulation, which can also
produce the arbitrary heat load pattern like thevarious type of the ELM. The absolute value of theone pulse energy density at present is still far lower
than ITER level, but it is expected to approach tothe ITER level by the upgrade and combination of
the all heating systems (ECH, NBI and ICRF).
4. Summary
ECH power modulation experiments in GAMMA
10 have been started in order to generate andcontrol the high heat flux for divertor simulation
studies. P-ECH is able to create the plug potentials
and the electron flow. From power scaling ofconfining potential and electron flux in GAMMA
10, the higher ECH power generates the higher
confinement potential and higher electron flux.
According to the increasing and modulating ECH
power, it is expected that the heat flux is enhanced
and controlled, which enables the ELM resemblingheat load pattern.
Acknowledgments
This work is partially supported by the grant-in-aid for Scientific Research from Ministry ofEducation, Science, Sports and Culture of Japan(23560997) and National Institute for Fusion
Science(NIFS)
Collaborativeprogram(NIFSKUGM050, NIFSKUGM053).
References[1] T. Imai et al: Fusion Science and Technology 59, 1T(2011) 1-8.