05pC03
300GHz 帯の高出力パルスジャイロトロンの開発
Development of a High-Power 300 GHz Pulsed Gyrotron
池内真司，山口裕資，笠純，小寺政輝，斉藤輝雄，立松芳典，小川勇，出原敏孝
S. Ikeuchi, Y. Yamaguchi, J. Kasa, M. Kotera, T. Saito, Y. Tatematsu, I. Ogawa and T. Idehara
福井大学 遠赤外領域開発研究センター
Research Center for Development of Far-Infrared Region, University of Fukui

250

30 % [4, 5].
Precise frequency measurement was done with aheterodyne receiver system. The measured
frequency of the TE14,2 was 293.98 GHz. The 3 dB
frequency width was about 3 MHz. The measured
frequency was lower than the resonance frequencyof the TE14,2 mode 294.95 GHz by 1.0 GHz. Thisdifference corresponds to a fabrication error in thecavity radius of about 11 μm. The TE14,2 mode isconverted to a Gaussian beam by an internal
mode convertor. The radiation pattern wasmeasured with an infrared camera. The measured
pattern was almost Gaussian and well reproduced
the calculated radiation pattern.
In addition, we tried to expand the pulse duration.
In the last annual meeting, we reported a longest
pulse duration T of 20 µs for a power level of 110
kW. Now, we have succeeded in longer pulse
oscillation up to 30 µs for 130 kW (Fig. 2). The
red line in Fig. 2 is pyro electric detector
signal. The pulse duration is mainly restricted byhighvoltage
breakdownaroundtheMagnetron-Injection Gun (MIG). It is planned toemploy oil-insulation in the MIG region.
[1] T. Notake et al., Phys. Rev. Lett. 103, 225002 (2009).
[2] T. Saito et al., Phys. Plasmas 19, 063106 (2012).
[3] Y. Yamaguchi et al., Phys. Plasmas 19, 113113 (2012).
[4] T. Saito et al., IRMMW-THz 2013, Mo5-3.
[5] Y. Yamaguchi et al., to be published in Plasmas Fusion Res.

801008015060

100405020cf = 1.32002468Ib (A)010 12Fig1. Beam current dependence of output powerand efficiency.

60
Vk (kV)

200 V = 24 kV
a-k

Efficiency (%)

Power (kW)Vk = 65 kV

20B = 11.17 T
Rb = 2.51 mm
Va-k = 22 kV

40Vk15Ic

1020

5Pyro.

00102030
Time (μ s)

Ib (A), Pyro. (a.u.)

We are developing a high power gyrotron in thesub THz band for use in the measurement ofcollective Thomson scattering in Large HelicalDevice. Following realization of new power records
at second harmonic oscillation [1, 2], a 300 GHz
band gyrotron with the fundamental harmonic
oscillation is under development aiming at morethan 200 kW and a pulse-duration of ~ 1 msec. The
oscillation mode was carefully chosen. A newelectron gun was also designed to produce a highquality laminar electron beam in a very highmagnetic field [3].
A cryogen-free 12 T superconducting (SC)magnet was introduced, and a cavity mode of TE14,2
was selected for a fundamental harmonic frequencyof 295 GHz. Over 200 kW oscillation is expected
for the beam voltage Vk of 65 kV and the beam
current Ib of 10 A. In the last annual meeting, wereported 175 kW as the maximum power at Vk = 60
kV and Ib = 14 A. This efficiency was 21 %. Over200 kW oscillation was not obtained because of low
oscillation efficiency.
Efforts for efficiency improvement have since
been made and stable oscillation [4, 5] and precisealignment between the gyrotron and the SC magnet.
Then, higher power was realized. Figure 1 plots theoutput power and efficiency as functions of Ib. The
maximum power has attained at 234 kW at Vk = 65
kV and Ib = 11 A. The efficiency is higher than040Fig. 2. Waveforms for the long pulse oscillation.