22P144-P
Long Pulse Test of 28 GHz - 1 MW Gyrotron for GAMMA 10 ECRHGAMMA 10 ECRH 用 28 GHz – 1 MW ジャイロトロンの長パルス試験
Hidetaka Nakabayashi 1, Tsuyoshi Kariya1, Tsuyoshi Imai1, Taku Eguchi1,
Ryutaro Minami1, Tomoharu Numakura1, Yoichi Endo1, Hitomi Aoki 1, Hideaki Iizumi1,
Ryo Kawarasaki1, Kazuhiro Nakazawa1, Keishi Sakamoto2
中林 英隆 1, 假家 強 1, 今井 剛 1, 江口 濯 1, 南 龍太郎 1, 沼倉 友晴 1,
遠藤 洋一 1, 青木 瞳 1, 飯泉 英昭 1, 河原崎 遼 1, 中澤 和寛 1, 坂本 慶司 212

Plasma Research Center, University of Tsukuba, 1-1-1, Tennodai, Tsukuba, 305-8577, Japan
Japan Atomic Energy Agency, Naka Fusion Institute, 801-1 Mukouyama, Naka, Ibaraki, 311-0193, Japan
1 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
2 日本原子力研究開発機構 那珂核融合研究所 〒305-0193 那珂市向山 801-1

Gyrotrons which oscillate high power microwave are important tools for Electron Cyclotron Resonance Heating(ECRH). In the GAMMA10 tandem mirror, gyrotron has been used to achieve high plasma performance. A 1 MW
gyrotron has been developed. The output power was achieved 1 MW in short pulse test, and 0.45 MW / 2 s in longpulse test. Moreover, the temperature rise of sapphire single disk window installed in 28 GHz 1 MW gyrotron wasmeasured. The temperature rise was 9℃ at 0.45 MW / 2 s. This result shows that 1 MW 1 s operation is possible.

2. Long Pulse Test of 28 GHz 1 MW Gyrotron
28 GHz 1 MW gyrotron has been designed andmanufactured in 2009.
Short pulse test was carried out prior to longpulse test. The SCM (Superconducting Magnet)
required for the gyrotron operation was borrowed
from National Institute for Fusion Science (NIFS).
We used, respectively, SCM#3 in 2009, SCM#1 in
2010, and SCM having the same magnetic field
distribution of SCM#3 in 2011. The magnetic fieldof SCM#1 is slightly different from SCM#3 at gun
region. Figure.1 shows the beam current
dependence of the output power in short pulse test.

Table.1 A set of design parameters of Presentand New 28GHz gyrotron
gyrotronFrequency
Output power
Pulse length
Beam current
Output mode
MIG
Output window

Output power [kW]1. Introduction
In the GAMMA 10 tandem mirror, ECRH
generates the axial ion confining potential and heats
electrons. Becouse the plasma performance
improves with increasing ECRH power, thedevelopement of 1 MW gyrotron which has higher
output power than the gyrotrons installed in
GAMMA has started in 2009. Table 1 shows a setof design parameters of present and new gyrotron.
New gyrotron is designed high power (1 MW) andlong pulse length (1 s), and installs the sapphire
window to ensure thermal stress of the output
window. In 2009, initial demonstration of 1 MW /short pulse (~ 1 ms) was achieved [1].
The results of detailed performance test of thehigh power and the long pulse operation arepresented.

PresentNew28GHz
0.5MW
1MW
0.1s
1s
20A40A
Gaussian likeDiodeTriodeAlumina
Sapphire

Short Pulse Test

1200

1000
800
600
28SCM(2011)
SCM #1(2010)
SCM #3(2009)

400
200001020304050

Beam current Ic [A]Fig.1 Beam current dependence of output powerof 28 GHz 1 MW gyrotron

As shown in Fig.1, the initial demonstration of 1
MW was achieved in 2009. However, the output
power in 2010 experiment was smaller than that in2009 with Ic > 20A. The maximum output power
was 0.69 MW. In 2011, the short pulse test wasLong Pulse Test

output power[kW]6004002002010
2011

00500

1000

1500

2000

pulse duration[ms]Fig.2 Pulse duration dependence of the output power

3. Temperature rise of the sapphire window
A little part of the output power is absorbed by
the output window due to the dielectric loss. One of
the factors of window break is the thermal stress bydielectric heating. The sapphire single disk window
is installed in 28 GHz 1 MW gyrotron. Thetemperature rise of the sapphire window wasmeasured to estimate maximum output power.
As shown in Fig.3, temperature rise of sapphire
window were measured by infrared camera througha BaF2 viewing port installed on the Matching
Optics Unit (MOU). As shown in Fig.4, the center
temperature increased proportionally with the pulse
duration, and the maximum temperature rise was
9.0 ℃ at 2.0 s with the output power of 0.45 MW.
As a result, the sapphire window temperature rise iscalculated about 10 ℃ at 1 MW 1 s output. We
found that temperature rise of the sapphire windowwill be no problem with the operation of 1 MW
several seconds.

Fig.3 Temperature rise of sapphire window
Temperature mesurementof sapphire window
temperature rising[℃]carried out with the SCM having the same magnetic
field of SCM#3. It is shown that the reduction of
the output power by using SCM#1 was improved.
Using the experimental operation parameters, thepitch factor
and thespread were calculated bygyrotron’s MIG simulation code. As a result, wefound that the reason of the output power reduction
was the deterioration of laminar flow of the electron
beam and the increase of
spread caused by thedifference of the magnetic field distributions at
MIG region of SCM#1 and SCM#3.
Next, the long pulse test was carried out. Figure.2
shows the pulse duration dependence of output
power. The output power and the pulse duration
were achieved 0.4 MW 1 s in 2010 and 0.45 MW 2
s in 2011. The thermal damage and the deteriorationof the withstand voltage weren’t observed in thisoperating region.
The output power was restricted by the voltage
and current capacity of the power supply in the longpulse test. And the pulse length was restricted by
the heat capacity of dummy load.

10864200123pulse duration[s]Fig.4 Pulse duration dependence of temperature risingof the gyrotron window

4. Summary
28 GHz 1 MW gyrotron was developed toachieve high plasma performance. The output
power was achieved 1 MW in the short pulse test.
The pulse duration was extended to 2.0 s with 0.45
MW in long pulse test. The maximum temperaturerise of the sapphire window was 9.0 ℃ with 0.45
MW / 2 s. From this experimental result, we canestimate that sapphire window temperature increaseis about 10 ℃ with 1 MW 1 s oscillation.
In future, after the improvement the power supply,
the long pulse test will be performed to aim at 1
MW / 1 s operation. In consideration of the result ofperformance test, design improvement of 28 GHz
gyrotron having higher power and longer pulse
length is being performed [2].
Acknowledgments
The author thanks the members of the NIFS ECHgroup and GAMMA10 group for their collaborationand valuable discussion during this study. This
work is partially supported by NIFS Collaborativeprogram (NIFS11KUGM050, NIFS11KUGM053).
References[1] M.Ota, et al.: Fusion Sci. Tech. 591T (2011) 238[2]T.Kariya, et al.: Plasma Conference 2011 (2011)22P143-P