29pB03
300 GHz, 100 kW 級パルスジャイロトロンの開発
Development of a 300 GHz, 100kW Pulsed Gyrotron
山口裕資，池内真司，斉藤輝雄，立松芳典，池田亮介，小川勇，出原敏孝
Y. Yamaguchi, S. Ikeuchi, T. Saito, Y. Tatematsu, R. Ikeda, 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
30X [mm]20100-10-20−30−30 −20 -10 010Y [mm]020300.2 0.4 0.6 0.8 1.0Signal Intensity [Arb. Unit]

Fig. 1 Radiation pattern at 280 mm from the outputwindow.

to the output window (Fig. 1). The signal intensity
is measured at intervals of 5 mm in both verticaland horizontal directions. A circular shaped, wellfocused beam is radiated. The output power wasmeasured with a water load. Figure 2 shows thedependence of the output power and the efficiency
on IB. The desired value of 100 kW was
successfully obtained at IB = 5.5 A with a relatively
high efficiency more than 30 %. The maximum
power reached at 191 kW under the present
operation conditions. The pulse duration of 110 kW
output was extended up to 20 μs, which wasrestricted by the power supply.
250Calc.

V = 60 kV

1K

200 IGUN = 50 A
αCavity150

0.8Exp.

~ 1.20.6Calc.

100
5000.4

Efficiency

Power [kW]In the field of nuclear fusion research, gyrotrons
play important roles in production, control, anddiagnostic of burning plasmas. We have aimed at
the development of a high power wave source foruse in the measurement of collective Thomson
scattering in Large Helical Device [1]. The
performance requirements are an oscillation
frequency around 300 ~ 400 GHz, an output powerof more than 100 kW, and a pulse-duration of ~ 1
msec. The main components including a cavity, aninternal mode-converter, and a magnetron-injection
gun are precisely designed.
A cryogen-free 12 T superconducting magnet
was introduced, and a cavity mode of TE14,2 wasselected at a fundamental harmonic frequency of295 GHz. A simulation result predicts that a powerof over 200 kW can be realized with anelectron-beam voltage VK of 65 kV, a current IB of
more than 10 A, and an electron velocity pitch
factor α (the ratio of perpendicular to parallel
velocities to the magnetic field line) of 1.2. A
complicated field distribution transmitted from thecavity is converted to a Gaussian like beam by theinternal mode converter. The configuration of a
Vlasov-type launcher and additional mirrors was
optimized under the restrictions for the available
room associated with the small magnet bore
diameter and the tube assembly processes.
The performance of the gyrotron is quitesensitive to the quality of the electron beam. As
follows from the result of previous study [2],special attention was paid to produce a laminarelectron flow with small velocity spread. An
optimum structure of the electrodes wasinvestigated with the EGUN code, and a quite small
velocity spread (less than 5 %) was obtained in thecavity for α = 1.2 [3].
The operation test was preliminary carried out
at a short pulse width (~ 5 μs) to find the optimum
operation parameters [4]. The oscillation of theTE14,2 mode was confirmed by the frequency
measurements with a Fabry-Perot interferometer.
The radiated wave distribution was evaluated byscanning a pyro-electric detector in a plane parallel

0.230-31/AUG./2012
Exp.: #457 - #531

05Exp.

I [A]

10015BFig. 2 Beam current IB dependence of output powerand efficiency[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., Plasma Fusion Res. 7, 1205004 (2012)[4] Y. Yamaguchi et al., IRMMW and THz 2012, Tue-A-3-5