05aC03
JT-60SA電子サイクロトロン波加熱電流駆動装置の2周波数化開発の進展
Progress in dual frequency system developments for electron cyclotron heating
and current drive in JT-60SA
小林貴之, 澤畠正之, 寺門正之, 平内慎一, 和田健次, 佐藤福克, 日向淳, 横倉賢治,星野克道, 高橋幸司, 梶原健, 小田靖久, 池田亮介, 森山伸一, 坂本慶司
KOBAYASHI Takayuki, SAWAHATA Masayuki, TERAKADO Masayuki,
HIRANAI Shinichi, et al.
原子力機構
JAEA
An electron cyclotron (EC) heating (H) andcurrent drive (CD) system is an important tool in
JT-60SA (Super Advanced) for highly localized
H&CD, and for start-up assist [1]. The millimeterwave frequency of 110 GHz, which was used in theprevious JT-60U experiments, is used in JT-60SA
in order to reuse the existing high-power millimeterwave components. In 2010, developments forrealizing a dual frequency ECH/CD system werestarted. The second frequency was chosen to be
138 GHz considering both ECCD efficiency intypical experimental scenarios planned inJT-60SA [2] and gyrotron design parameters [3]. In
2012, short pulse (< 0.1 s) operation of the first dual
frequency gyrotron for JT-60SA was carried out.
The output power higher than 1 MW and 0.5 MW
were obtained at 110 GHz and 138 GHz,
respectively, with the oscillation efficiency (notincluding efficiency enhancement effect bycollector potential depression) of higher than 30%,
which is sufficiently high for long pulse operation
at > 1 MW [3].
In 2013, the first long pulse operation of thedual frequency gyrotron was carried out. So far, weachieved oscillations of 1 MW for 10 s at both
frequencies. Moreover, high efficiency of > 30%
was obtained by optimizing an electron pitch factor
for each frequency by changing anode voltage ofthe triode type magnetron injection gun before
oscillation that is not possible by a diode typemagnetron injection gun. The measured diffraction
loss in the gyrotron is comparable level with theprevious 110 GHz long-pulse gyrotron, which
achieved oscillations of 1 MW for 70 s and 1.4 MW
for 9 s, so far, as shown in Table. 1. Thus we expectthat the dual frequency gyrotron has a long pulse
capability of at least 1 MW for 70 s. The pulse
length was limited by an increase in the pressure in
the dummy load, so far, while it was saturated andthe peak pressure during an oscillation wasdecreased shot by shot. Thus further pulse length

expansion is possible.
Table. 1 Comparison of the diffraction losses (Dloss) in
the gyrotron and the MOU of the previous 110 GHz
long-pulse gyrotron (1-freq.), and the dual frequency
gyrotron (2-freq.). Tentative power and pulse lengthachieved so far are also shown.
Gyrotron
1-freq.
2-freq.
Frequency [GHz]
110
110
138
Dloss in gyrotron [%]
3.0
3.8
3.2
Dloss in MOU [%]
7.1
3.7
3.5
Power and pulse 1MW, 70s
1MW,1MW,length
1.4MW, 9s
10s
10s

In the above long pulse operation, thediffraction loss in the matching optics unit (MOU)
for 138 GHz was comparable level with 110 GHz
and much lower than the single frequency gyrotron
even though phase correcting mirrors optimized for
only 110 GHz was used. Thus, it may be possible touse the same mirrors for both frequencies. However,detail evaluation of mode purities is required
because the mode purity is an important parameterfor both transmission loss and the beam quality
launched into the tokamak. We will evaluate themode purity in a long transmission line (~ 60 m) for
both frequencies with high-power in near future.
Optical design of the launcher, which injects
millimeter waves into the tokamak, has been carriedout. In calculation, it was confirmed that the beamwidth in poloidal direction for 138 GHz was almost
the same as that of the 110 GHz while the beamwidth in toroidal direction for 138 GHz was
narrower than that of the 110 GHz.
Developments of transmission line and control
system will be presented.
[1] Y. Kamada et al., Nucl. Fusion 53 (2013) 104010.
[2] A. Isayama et al., Plasma Fusion Res. 7 (2012)
2405029.
[3] T. Kobayashi et al., Trans. Fusion. Technol. 63, 1T(2013) 160.