[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] ABSTRACT: A Terahertz gyrotron has been developed. We succeeded in obtaining magnetic field 20.1 T with Ice-type pulse magnet. We started experiment of electron beam propagation in the resonance cavity. It was confirmed that the most electrons passed the gyrotron tube with the magnetic field 10 T and the electron beam voltage-10kV.
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] ABSTRACT: High frequency gyrotrons are characterized by their capacity of delivering high powers in millimeter to submillimeter wavelength ranges and their frequency step-tunability due to an alternation of the operating mode. In order to widen the use of high frequency gyrotron, we need a functional quasi-optical system to treat a Gaussian beam converted from gyrotron output. The necessary characteristics are compatibility with tenability of output beam waist size, which enables us to ensure an effective coupling of beam to sample and waveguide. Such a function is realized only by moving a focusing mirror. The focusing mirror with focal length of 300mm offers a tunable range from 6.78mm to 32.82mm.
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] ABSTRACT: The Large Orbit Gyrotron (LOG) device has been constructed by using a permanent magnet system whose intensity is around 1 T. LOG oscillates efficiently when high harmonic degree s is equal to TEmm mode m of in the cavity mode. Therefore, high harmonic becomes easy compared with a usual gyrotron, and the mode selection improves, too. The operation test of LOG was successfully at the second harmonics by the pulse operation (pulse with: 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.
[Show abstract][Hide abstract] ABSTRACT: The high harmonic gyrotron using the short pulse high energy electron beam is being developed. In order to develop this gyrotron, a pulse power supply of the electron gun was made. The pulse power supply is utilized a pulse forming network system. In this report, the result of operation test of the pulse forming network is presented. Typical output waveform of pulse forming network is 100kV of voltage, 1.7kA of current and 1.2 μ s of pulse width.
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] ABSTRACT: Frequency stabilization of submillimeter wave gyrotron was achieved by reducing the temperature variation of cooling water. Correlation between variations of the frequency and the temperature of cooling water is confirmed by the experiment. Simple analysis using heat conduction method can explain the experimental results reasonably.
[Show abstract][Hide abstract] ABSTRACT: 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. Because spatial and wave number resolutions are improved by focusing the beam and increasing the scattering angle, a submillimeter wavelength beam is most suitable for the measurement. Up to now, molecular vapor lasers and backward-wave oscillators have been used as the principal power sources. However, their output powers are lower than 0.5 W and 10 mW, respectively Application of high frequency gyrotron is effective in improving the C/N ratio 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. A final goal is to produce an optimal probe beam (high quality, intense submillimeter wave beam by using a new transmission line and to apply it to plasma scattering measurements with the aim of optimal performance of the measurement.
[Show abstract][Hide abstract] ABSTRACT: In order to make a flat top pulse magnetic field, a testing circuit consists of power sources and pulse forming circuit. A program code is made to calculate the flat top magnetic field in axial direction due to a series of coils. The coils size, number of coils, and the target of field (40 tesla) are given. The coils position and current density is computed by Newton method.
[Show abstract][Hide abstract] ABSTRACT: The frequency characteristics of gyrotrons can be precisely measured by the harmonic mixing techniques with a Schottky barrier diode harmonic mixer and a phase-locked millimeter wave Gunn oscillator. As the first step, those for the free-running gyrotron at 300 GHz band are measured. The results show that the short-term spectral bandwidth is about 10kHz at most and the slow fluctuation of the center frequency of oscillation is found about 10MHzp-p. As point-contact mixers are known to work even at high frequencies and the output signal levels of gyrotron are sufficiently high, the frequency measurement using this method will also be useful at up to 1THz.