23P170-B
Design of an antenna system for millimeter wave transmission
to an ESR echo experiment system, III
ESR エコー実験
エコー実験システム
実験システムへのシステムへのミリへのミリ波伝送用
ミリ波伝送用アンテナ
波伝送用アンテナ系
アンテナ系の設計 III
Takanori Ozeki, Yoshinori Tatematsu, Yuusuke Yamaguchi, Seitaro Mitsudo,
Yutaka Fujii, Isamu Ogawa, Toshitaka Idehara, Teruo Saito
尾関隆則，立松芳典，山口裕資，光藤誠太郎，
藤井 裕，小川 勇，出原敏孝，斉藤輝雄
Research Center for Development of Far-Infrared Region, University of Fukui
3-9-1 Bunkyo, Fukui 910-8507, Japan
福井大学遠赤外領域開発研究センター 〒910-8507 福井市文京3-9-1
An ESR echo experimental system is now being developed, where a high power gyrotron is applied as aradiation source. A transmission system consisting of a Vlasov launcher and six mirrors has been designed.
It transmits the beam from the gyrotron to the ESR system. The Vlasov launcher convects the EM wave of
the circular TE0,2 mode oscillated in the gyrotron cavity to a linearly polarized Gaussian-like beam. The
beam shape is farther fixed after reflection by the six mirrors and a Gaussian beam with the radius of 8 mmis injected into the ESR system.

delivering the EM wave from the gyrotron to theentrance of the ESR experiment system (ESR-ES),in which the EM wave is convected to a linearlypolarized Gaussian beam.

1. Introduction
Development of high frequency and highpower gyrotrons has been progressed in FIR FU.
Their applications are measurement of fusion
plasma, electron spin resonance (ESR)
spectroscopy, a protein analysis and so on.
Gyrotron FU CW VIIA has been developed as aradiation source of the ESR echo equipment forinvestigating the characteristic of the electronic
spin system of a substance by high resolution oftime under a strong magnetic field. In the ESR
echo measurement, the incident EM wave isrequired to be a linearly polarized Gaussian beamwith an appropriate diameter. The purpose of thisresearch is design of a transmission system of

2. Transmission system
Figure 1 shows a schematic of the transmission
system. The radiation beam emitted by the Vlasov
launcher is reflected by five ellipsoidal mirrors andone plane mirror delivered to the incident point ofthe ESR-ES. As a placed outside of the gyrotron
radiation source, Gyrotron FU CW VIIA is applied.
The oscillation mode of TE0,2 with the frequency of
153 GHz is chosen to the ESR experiment. An EM
wave propagated through a waveguide with thezyx

Fig.1 Transmission system

Fig.3 Poynting flux distribution in an incident point

1.5

Electric field E (a.u.)

3. Vlasov launcher
We manufactured the Vlasov launcher andconfirmed its performance. The radiation pattern ofthe beam launched from the Vlasov launcher wasobserved with an IR camera as the temperature
increase on a vinyl chloride plate placed
perpendicular to the beam propagating direction.
Figure 2 shows a radiation pattern at the distance of300 mm from the Vlasov launcher. Vertical andhorizontal sizes are equivalent to 100 mm in Figure
2. An oval pattern was observed, which indicates
the Vlasov launcher well converted the EM wave toa Gaussian-like beam.

flux distribution at the incident point. The
coordinated x,y,z is defined in figure 1. It is almost
circular. Figure 4 shows its profile the Poynting flux
along y-axis in Figure 3. The profile is fitted to a
Gaussian distribution and the fitted spot size w is 8mm, which is within the desired value. Moreover,Figure 5 shows the three components of the electricfield and, y component is the dominant. Therefore,
the beam is almost linearly polarized along y-axis.
The almost linearly polarized Gaussian beam canbe injected to ESR-ES by the designed
transmission system.

Poynting flux (a.u.)

diameter of 28 mm in the gyrotron and radiatedfrom the window. A linear taper attached outside of
the gyrotron window reduces the waveguidediameter from 28mm to 10 mm. The Vlasov
launcher consists of a step-wise waveguide with thediameter of 10 mm and a parabolic mirror. The EM
wave is convected by the Vlasov launcher and a
Gaussian-like beam is radiated by the launcher. If
radiated beam is directly transmitted to the ESR-ES,
the beam size becomes very large since the beam
expands. Therefore, five ellipsoidal and one plane
mirror are installed to keep the beam size smallenough to make the beam radiated mirror sizes as
small as possible. In result, the mirror sizes are also
kept small. According to the requirement in theexperiment, the beam spot size w is set to be about
10 mm at the entrance of the ESR-ES.

1.00.50.5-500y (mm)

100 mm

100 mmFig. 2 A radiation pattern of the beam radiated from the Vlasov
launcher in measurement with an IR camera

4. Design of the ellipsoidal mirrors
The Gaussian-like beam radiated from theVlasov launcher is delivered to the entrance ofESR-ES after reshaped to a Gaussian beam by fiveellipsoidal mirrors. The surfaces of the mirrors havebean designed by calculation of the beam profile atthe entrance. The calculation was performed with acode based on Fresnel-Kirchhoff's diffraction theory.
Figure 3 shows a calculation result of a Poynting

Fig.4 Calculated Poynting flux
along y-axis

501.0ExEyEz

0.50.0-50050y (mm)Fig.5 The electric field componentsof the radiation beam

5. Conclusion
We have designed the transmission system which
delivers the radiation from the gyrotron to ESR-ES
after converting it to a Gaussian beam. The almost
linearly polarized radiation beam with the spot sizeof 8 mm was obtained in calculation. This system
will be now manufactured and completed at the endof this year.