22P145-P
Design and Development of Electron Cyclotron Heating and Current Drive
System for JT-60SA
JT-60SAに向けた電子サイクロトロン加熱・電流駆動装置の設計と開発
Takayuki Kobayashi, Akihiko Isayama, Katsumichi Hoshino, Kenji Yokokura, Mitsugu Shimono,
Masayuki Sawahata, Sadaaki Suzuki, Masayuki Terakado, Shinichi Hiranai, et al.
小林貴之，諫山明彦，星野克道，横倉賢治，下野貢，澤畠正之，鈴木貞明，寺門正之，
平内慎一，和田健次，佐藤福克，日向淳，森山伸一, 坂本慶司
Japan Atomic Energy Agency
801-1, Mukoyama, Naka, Ibaraki 311-0193, Japan
日本原子力研究開発機構 〒311-0193 茨城県那珂市向山801-1
Design and development of high-power long-pulse electron cyclotron heating and current drive system for
JT-60SA have been progressed. High power transmission test using newly developed components with awaveguide inner diameter of 60.3 mm was carried out. A conditioning operation was progressed to 5 s withan output power of 0.5 MW, so far, within a few weeks without significant trouble. The other progress wasmade to develop the dual frequency system with an additional frequency of 137.6 GHz in order to enhance
operation regime. Output power higher than 1 MW with oscillation efficiency much higher than 30% wasobtained for preliminary design of a dual frequency gyrotron for both 110 GHz and 137.6 GHz.

1. Introduction
Electron cyclotron Range of Frequency(ECRF) heating and current drive system plays
important roles for super-conducting tokamak,such as for localized electron heating and currentdrive, for stabilizing neoclassical tearing modes(NTMs), for assisting plasma start-up, and forwall cleaning. In JT-60 Super-Advanced(JT-60SA), an ECRF system is specified asinjection power of 7 MW, flat top pulse length of
100 s with a millimeter wave frequency of
110 GHz [1]. In order to satisfy the above
requirements, design and development of ECRF
system have been carried out by improving theprevious ECRF system in JT-60 [2, 3]. Recently,
an application of a dual frequency ECRF system
in JT-60SA was discussed [4, 5], and a design ofa dual frequency gyrotron has been started. In thispaper, present status of ECRF system design isdescribed in Sec. 2. Progresses in high-power
long-pulse millimeter wave generation andtransmission experiments are shown in Sec. 3 anddesign of a dual frequency gyrotron is describedin Sec. 4, and progresses on ECRF system designand developments toward JT-60SA aresummarized in Sec. 5.

especially near the JT-60SA tokamak, design oflayout of transmission line, launcher and stages is
one of the important issues. Since the conceptual
design of the ECRF launcher was finished, we havestarted to design the layout of stage of launcher andtransmission line by using CATIA. Figure 1 showsa present model of the ECRF system in the torus
hall. The structure of the stages and space formaintenance are under discussion.

2. Status of ECRF System Design
Conceptual design of ECRF system had been
carried out, and the design has been revised in order
to be consistent with the latest design of JT-60SA.
Since many systems are installed in the torus hall,

3. High-power Long-pulse Experiments
In 2010, we achieved an oscillation of 1 MW for
31 s by using an improved gyrotron, of which mode
converter was revised to reduce diffraction loss in
the gyrotron [6]. However, the transmission line
used to test the gyrotron limited the pulse length up

Fig.1. Present model of ECRF system in the JT-60SA
torus hall.

4. Dual Frequency Gyrotron Design
A dual frequency ECRF system has been
designed, in which the most challenging task is thedevelopment of a dual frequency gyrotron. From aview point of plasma experiments in various
experimental conditions, an additional frequency
between 130 GHz and 140 GHz in addition to
110 GHz is useful for extending operation regimeof the ECRF system in JT-60SA, and the frequencyof 137.6 GHz was selected from discrete
frequencies of gyrotron oscillation modes to satisfy
suitable experimental condition. At this frequency,
the thickness of CVD diamond windows(2.291 mm) used as an output window of a gyrotron
and a torus window is thicker by 4/3 than that of theprevious one (1.715 mm). The oscillation modes for
110 GHz and 137.6 GHz are TE22,8 and TE27,10,
respectively, with the cavity radius of 22.84 mm.
The radius is slightly larger than that of theprevious cavity (19.8 mm) operated at TE22,6, andthe cavity heat load was reduced from ~1.2 kW/cm2
to ~0.8 kW/cm2 for 110 GHz. Figure 2 shows a rf
output power and efficiency of the newly designed
gyrotron cavity for both 110 GHz and 137.6 GHz.
The output power and efficiency at the window will
be slightly lower than these values due todiffraction and Ohmic losses in the gyrotron. It wasclarified that an output power higher than 1 MW is
obtained with oscillation efficiency much higher
than 30% for both frequencies even with relatively
low electron pitch factor of 1.1. A quasi-opticalmode converter was designed using LOT/Surf3d
code [7]. The Gaussian like patterns were obtainedat the output window for both frequencies and thebeam center was placed at the center of the outputwindow. The design of other parts of the gyrotron isthe same as that of the improved 110 GHz gyrotron
for JT-60 and 170 GHz gyrotron for ITER [8]. The
design of the gyrotron was finished and fabrication
has been started in Toshiba Electron Tubes andDevices Co., Ltd. The new gyrotron will bedelivered by the end of March, 2012, andconditioning operation will be started from April,2012.
Vbeam = 85 kV

3100

P: RF power [MW]P(110)P(137)
80
Power260401Efficiency

η: Efficiency [%]to 31 s (~30 MJ). In order to achieve pulse length of100 s by reducing mode conversion loss at miter
bends, we revised the transmission line byincreasing inner diameter of waveguide from31.75 mm to 60.3 mm. Moreover, protection jackets
of bellows of inlet and outlet of matching optics
unit (MOU), which was significantly heated bydiffracted waves, was developed. After these
improvements, we restarted to operate the gyrotron,and pulse length reached to 5 s so far at output
power of ~0.5 MW without any significant troubles.

20
η(110)
η(137)
0102030405060070

Beam current [A]Fig.2. Simulation result of beam current dependenceof generated rf power and efficiency of the newly
designed gyrotron cavity. The cavity magnetic field
was optimized to obtain the highest efficiency withthe electron pitch factor and beam voltage of 1.1 and85 kV, respectively.

5. Summary
The design of ECRF system has been progressedin the system layout in torus hall.
Transmission line with 60.3 mm waveguidecomponents was installed for reducing mode
conversion loss at miter bends, and conditioning
operation was progressed to 5 s at the output powerof 0.5 MW without any significant troubles. An
oscillation of 1 MW for 100 s at 110 GHz, which isrequired in JT-60SA, is expected to bedemonstrated in the near future.
For extending operation regime of the ECRF
system in JT-60SA, a dual frequency gyrotron was
designed, and fabrication has been started. The new
gyrotron will be tested by improving transmission
line for broadband frequency.
AcknowledgmentsTheanthers
wouldliketothankMr. Y. Mitsunaka (Toshiba Electron Tubes andDevices Co., Ltd.) for useful discussion on the dual
frequency gyrotron development.
References[1] Y. Kamada et al., Nucl. Fusion. 51 (2011) 073011.
[2] Y. Ikeda et al., Fusion Sci. Technol. 42 (2002) 436.
[3] S. Moriyama et al., Nucl. Fusion 49 (2009) 085001.
[4] JT-60SA research plan Version 2.1, 2011, February,JT-60SA Physics Unit.
[5] A. Isayama et al., to be submitted in Plasma andFusion Research.
[6] T. Kobayashi et al., Nucl. Fusion 51 (2011) 103037.
[7] J. Neilson, IEEE Plasma Sci. 34 (2006) 635.
[8] K. Sakamoto et al., Nature Phys. 3 (2007) 411.