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  • 豊 板倉, 勇 小川, 敏孝 出原
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    ABSTRACT: High frequency gyrotrons are characterized by their capacity to deliver high power in the millimeter to the submillimeter wavelength range and their frequency step-tunability due to the alternation of the operation mode. Before these gyrotrons can be used as radiation sources, it is necessary to convert the outputs into well-collimated, linearly-polarized beams. Gyrotrons produce hollow cone-shaped beams, which are far from what is usually required. We have constructed a quasi-optical system intended to convert the radiation of the Gyrotron FU VA into bi-Gaussian beam. The system consists of a quasi-optical antenna and an ellipsoidal mirror. The former converts the gyrotron radiation of TE0n and TE1n operating modes into linearly-polarized beam and the latter produces the far-field pattern. The measurements of the output beam have demonstrated that the developed system can produce high quality beams from the outputs of TE03 and TE13 operating modes.
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    ABSTRACT: The high frequency gyrotrons are characterized by their capacity to generate powerful radiation. However, a gyrotron produces a spreading radiation with a spatial structure of the TEmn waveguide mode. Because the polarization, the phase and the intensity of the radiation have complicated profiles, such radiation is not suitable for the applications. In this respect, a Gaussian beam (TEM00 mode) with a linear-polarization, simple profiles of the intensity and the phase is more suitable for effective irradiation of the sample and transmission using mirror system and waveguide. If the Gaussian beam is obtained from gyrotron output, the versatile transmission system for a Gaussian beam will be realized. In this system, con-focal mirror systems are installed in a special shaft which goes through the second floor, the third floor and the forth floor of the building of the Reserch Center for Development of Far-Infrared Region. The Gaussian beam can be transmitted to those three floors keeping the waist size of the output beam equal to that of the input beam by rotating and moving the flat mirror located at the third floor. The cold test of the system was carried out using a Gunn oscillator (120GHz) as a radiation source.
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    ABSTRACT: Density fluctuations in magnetically confined plasmas are important physical quantities to be measured for the basic study of plasma confinement, aince the density fluctuations are theoretically expected to enhance the energy loss of the confined plasma across the magnetic field. The scattering method with electromagnetic wave makes it possible to observe frequency and wavenumber of the fluctuations directly with a high spatial and wavenumber of the fluctuations directly with a high spatial resolution. The performance of plasma scattering measurement (S/N ratio, the spatial and wave number resolutions) depends on intensity, wavelength range and quality of a probe beam. A submillimeter wavelength range and quality of a probe beam. A submillimeter wavelength beam is the most suitable for improving both the spatial and the wave number resolutions. Application of high frequency gyrotron is effective in improving the S/N ratio of the measurement because of its capacity to deliver high powers. In order to meet the high requirements need for measurement, the output radiation of the gyrotron FU Ⅳ has been stabilized by introducing a smoothing circuit in the high-voltage power supply. In addition, conversion of the output radiation into a Gaussian beam ‘TEM00 mode) is necessary for an effective transmission and irradiation of the plasma by a well-collimated probe beam.
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    ABSTRACT: Scattering measurements of density fluctuations gives important information to understanding of the mechanisms of plasma confinement and plasma heating. The spatial and wave number resolutions and the S/N ratio of measurement depend on the wavelength range, the size and the intensity of a probe beam. A submillimeter wave beam to offer small scattering volume and relatively large scattering angle is suitable for improving the spatial and wave number resolutions. Application of high frequency gyrotron is effective in improving the S/N ratio of the measurement because of their capacity to deliver high powers. It is necessary to stabilize the output of gyrotron to improve the performance of the scattering measurement. The output of gyrotron was stabilized (ΔP/P~0.2%, Δƒ~10kHz) by introducing the smoothing circuit that consisting of resistor, an induction coil and a capacitor into the high-voltage power supply.
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    ABSTRACT: The Large Orbit Gyrotron (LOG) device has been constructed by using a permanent magnet system whose intensity is around 1 T. The operation test of LOG was successfully at the third, the fourth and the fifth harmonics by the pulse operation (pulse width: 1 ms). The high efficient and single mode operation at each harmonic in obtained by use of TEn11 cavity mode. The operation results of the LOG are summarized in this paper.
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    ABSTRACT: In conventional gyrotrons are used several 10 keV electron beam. If a higher energy electron beam is used, the energy conversion efficiency from the beam electrons to the electromagnetic wave should be increased. We have begun the development of a high harmonic gyrotron using a short pulse higher energy electron gun is presented. The pulse generator is the blumlein type pulse forming network using series of inductors and capacitors. The designed output waveform is a square pulse with the flat part of 1 μs. The energy and current are increased up to 120kV and kA, respectively.
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    ABSTRACT: Plasma scattering measurement is effective technique to observe low frequency density fluctuations (ƒ<1 MHz, k=10 cm-1) excited in plasma. The spatial and wave number resolutions and the S/N raito of measurement depend on the wavelength range, the size and the intensity of a probe beam. A well-collimated, submillimeter wave beam to offer small scattering volume and relatively large scattering angle is suitable for improving the spatial and wave number resolutions. Application of high frequency gyrotron is effective in improving the S/N raito of the measurement because of its capacity to deliver high powers. Unlike a molecular vapor laser, a gyrotron generates spreading radiation with TEmn mode structure. It is therefore necessary to convent the output radiation into a Gaussian beam (TEM00 mode), which is suitable for an effective transmission and a well-collimated probe beam. The output radiation of TE16 mode (ƒ=354 GHz, p~100 W, pulse duration 1 s) is converted into bi-Gaussian beam by a quasi-optical system consisting of a quasi-optical antenna and a focusing mirror.
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    ABSTRACT: Stabilization of the gyrotron output power and frequency is necessary for the experiments using gyrotron radiation for spectroscopy in many fields. The reduction of the fluctuations in the anode and cathode voltage of the electron gun is effective in the stabilization. Modulation of the output power has been achieved by modulating the velocity distribution function of beam electrons through modulation of the anode voltage of the electron gun. Detailed experimental studies have been carried out for CW operation mode of the submillimeter wave Gyrotron FU Ⅳ. In this report, the results are summarized and some theoretical considerations are presented.
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    ABSTRACT: Carrier properties of n-type InSb doped by tellurium at liquid nitrogen temperature have been investigated measuring the transmission of millimeter wave (119.3 GHz) through a sample placed along a magnetic field with intensity up to 4 T. In the n-type InSb, the millimeter wave injected with a linear polarization will suffer a rotation of its plane of polarization. This rotation angle serves as a function of the magnetic field containing the parameter of free career. Using such technique, the electron density and the effective mass in n-type InSb have been estimated.
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    ABSTRACT: 福井大学遠赤外領域開発研究センターでは,高周波ジャイロトロンの開発とその応用研究を展開している.最近ジャイロトロンの発振周波数として当センターの持つ世界最高記録を更新し,1THz超の発振に成功した.また,セラミック焼結・核融合プラズマ診断・遠赤外領域超低温物性研究・蛋白質解析、新医療技術開発等への応用のため,数100GHzから1THzに至るCWジャイロトロンの開発を進めている,本講演では,当センターにおける高周波ジャイロトロン開発と応用に関して,最近の研究成果を発表するとともに,今後の研究の展開を示す. Research Center for Far-Infrared Region, University of Fukui is aiming to development and application of high frequency gyrotrons. We have recently succeeded in over-1THz oscillation of gyrotron improving our own world record. We are developing cw gyrotrons with frequencies of several hundred GHz to 1THz for application to ceramic sintering, fusion plasma diagnostics, low temperature condensed matter physics in far-infrared region, protein analysis, new medical processing technology, etc. In this talk, our recent results and future prospects of high frequency gyrotron development and applications in FIR FU are presented.
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    ABSTRACT: Dynamic Nuclear Polarization (DNP) could open sensitivity enhancement of Nuclear Magnetic Resonance (NMR) for application of analysis of complicated protein molecules. The so-colled DNP-NMR is well known method in low field and low frequency NMR. However, high frequency DNP-NMR is needed for high spacial resolution of the measurement. We have developed a sub-THz Grotron FU CW VII for 300 MHz and 600 MHz DNP-NMR. The cavity radius is 2.175 mm, length is 19 mm. Designed cavity mode are TE_<421> (f=203.75 GHz)for 300 MHz DNP-NMR and TE_<161> (f=395.28 GHz)for 600 MHz DNP-NMR. The output power are 200 W (I_b = 350 mA) and 50 W (I_b = 200 mA) respectively. In this report, operation results of Gyrotron FU CW VII are presented.
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    ABSTRACT: The main purpose of our research is to develop the tera-hertz wave technique of DNP(Dynamical Nuclear Polarization)-NMR for the protein structural analysis. For such purpose, we have developed two DNP systems (only at room temperature); one is an X-band system with a YIG oscillator and a TWTA, and the other is a tera-hertz wave system with a gyrotron. At first, we have demonstrated the 1H-DNP experiments on BDPA-doped toluene solution at 11.4 GHz ESR frequency. Increase of the signal intensity of 1H-NMR (about 20 times at maximum) has been observed when the microwave was irradiated to the sample effectively by the sample-shuttle system. The tera-hertz wave experiments have been also performed with a gyrotron CW-1, however, we could not avoid increase of the sample temperature, and the DNP effect was not confirmed. We are now looking for the solution to avoid the increase of sample temperature while the high power microwave is irradiated.
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    ABSTRACT: Scattering measurements of density fluctuations gives important information to understand of the mechanisms of plasma confinement and plasma heating. A submillimeter wave beam to offer small scattering volume and relatively large scattering angle is suitable for improving the spatial and wave number resolutions. Application of an intense, high quality, well-collimated probe beam is effective in improving the performance of the measurement. Such probe beam is produced by stabilization of the high frequency gyrotron output and its conversion into a Gaussian beam.
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    ABSTRACT: We are currently developing instruments and techniques for the sub-millimeter wave dynamical nuclear polarization (DNP) experiment. Our sub-millimeter wave DNP system is composed of a sub-millimeter gyroteon (gyrotron FU-Ⅳ), a 400 MHz NMR system and a 17 T superconducting magnet. We have developed the NDP probe for the room temperature experiment: ESR detection system has been checked with a Gunn oscillator (ƒ=115 GHz); 1H-NMR detection system has been measured at ƒ=361 MHz under B=8.5T, which corresponds to the ESR field of TE32 mode of gyrotron FU-Ⅳ. In order to find the standard sample for the DNP experiment, we have also developed an X-band DNP system.
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    ABSTRACT: A permanent magnet type gyrotron using 4th harmonics with over 100 GHz was investigated. Although the authors have already designed the basic magnetic circuit (C9 and C11 model), an improved magnetic circuit (C13 model) is investigated and finely tuned in order to manufacture the magnet circuit in practice. Also, the magnet circuit is controlled at the temperature of 30 C using rubber heater in order to hold a constant magnetic field distribution in spite of temperature changes. Good electron beam orbits were obtained in the improved model (C13) by simulation. So, the magnet circuit based on the improved model was manufactured. The obtained magnetic field strength and its distribution were well coincided to the calculated ones after the field adjustment. The electron beam orbits simulation based on the measured results showed good results.
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    ABSTRACT: A novel design of a quasi-optical system for conversion of gyrotron output radiation into a well-collimated beam is presented and manufactured. The proposed system of the beam conversion consists of a quasi-optical antenna and elliptical mirror. This system can be used as a transmission line for frequency tunable gyrotrons operating at TE0n and TE1n modes. The system can successfully convert the TE0. mode (ƒ=194 GHz) and TE13 mode (ƒ=163 GHz) output of a Gyrotron FU VA into a bigaussian-like beam.
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    ABSTRACT: Amplitude modulation of the gyrotron output has been achieved by modulation of the velocity distribution function of beam electrons through modulation of the anode voltage of the electron gun. Detailed experimental studies have been carried out for CW operation mode of the submillimeter wave Gyrotron FU IV. In this report the results are summarized and some theoretical considerations are presented.
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    ABSTRACT: In this paper we discuss some basic aspects of the irradiation of living bodies with submillimeter electromagnetic waves using open vent antennas. The experiments have been performed on beef livers. The waveguide vent antennas with diameter of 28 mm or 5 mm and a horn antenna intended for such irradiation were investigated by means of computer simulation. The simulation results for the distribution of irradiation intensity agree qualitatively with the experimental data obtained at frequency 302 GHz.
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    ABSTRACT: The novel focusing mirror based on the shifting of the beam phase according to Gaussian optics enabled us to realize a focusing element with different focal length in different derections and to convent gyrotron output into Gaussian-like beam. In this paper, we compare the quality of beams produced by the new system (which includes the novel focusing mirrors) and conventional system having a quasi-optical antenna, an ellipsoidal mirror and two parabolic mirrors.
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    ABSTRACT: In order to investigate the experimental technique and the high magnetic field effect in the dynamical nuclear polarization (DNP) experiments,the X-band ^1H-DNP and the high power sub-THz wave irradiation experiments have been performed on a toluene solution of α,γ-bisdiphenylene-β-phyenylallyl (BDPA) radical at room temperature. We have established the sample-shuttle X-band DNP experimental system,and investigated the external magnetic field,the microwave power and ^1H-T1^-1 dependences of Overhauser enhancement factor ε. A maximal signal enhancement of approximately -19 has been observed. As for the sub-THz wave experiments,we have constructed the NMR and ESR measurement system for the experiments under the magnetic field of ~10.7 T,with a high power light source gyrotron CW-I (TE22,8 mode,ƒ~299.23 GHz). When the high power sub-THz wave of a gyrotron was irradiated on the toluene solution in order to confirm the evidence of DNP,the sample has evaporated due to the electromagnetic wave heating.