Investigation of Mode Interaction in Harmonic Sub-THz Gyrotron

Journal of Infrared, Millimeter, and Terahertz Waves - Within the frame of a non-stationary self-consistent model, we have investigated the regimes of simultaneous oscillations at two different...     

Higher Harmonic Operations of Submillimeter Wave Gyrotrons (Gyrotron FU Series)

Higher harmonic operation of gyrotrons is necessary to obtain high frequencies. Some gyrotrons included in the Gyrotron FU series developed at Fukui University have achieved operation at the third and even fourth harmonics of the electron cyclotron frequency. The output lies in the millimeter to submillimeter wavelength range and the output powers are several watts to several tens of watts. In this paper, the gyrotrons and the conditions under which they operate are described in detail.     

Simulation of Mode Interaction in the Gyrotron FU CW I

A series of experiments carried out in order to study the operational performance and oscillation characteristics of a 300 GHz/3.5 kW gyrotron FU CW I have demonstrated a complicated behaviour which is attributed to multimoding phenomena. In this paper we present and discuss some initial results from computer simulation of mode interaction in this tube. They give a better insight in the underlying processes, possible excitation conditions of various competing modes and suggest some directions for continuation of this investigation.     

Nonlinear Regime of Amplitude Modulation in Submillimeter Wave Gyrotrons (Gyrotron FU III and IV)

Amplitude modulation in submillimeter wave gyrotrons resulting from the modulation of the anode voltage of electron gun is studied in detail. Computer simulations for the nonlinear regime, where the modulation rate of the anode voltage is not proportional to the amplitude modulation, model the experimental results quite accurately.     

Influence of Possible Reflections on the Operation of European ITER Gyrotrons

The theory describing the influence of reflections on operation of gyrotrons with radial output is used for evaluating the effect of reflections on the operation of the ITER 170 GHz 2 MW coaxial cavity gyrotron, which is under development, and the 170 GHz 1 MW cylindrical cavity gyrotron as a fall back solution.     

Development of a Compact sub-THz Gyrotron FU CW CI for Application to High Power THz Technologies

For application of high frequency gyrotron to high power THz technology, Gyrotron FU CW series is being developed in FIR FU. Gyrotron FU CW CI is developed as one of sub-THz gyrotrons included in the series. The advantage of the gyrotron is compactness using a compact superconducting magnet and compact power supply system, which makes the accesses of the gyrotron to applied large-scale devices easier and extends the applications of gyrotron to wider fields. The designed frequency and cavity mode are 394.5 GHz and TE₂₆ mode for application to the 600 MHz DNP-NMR spectroscopy. As the operation results, the frequency and the output power were 394.03 GHz and around 30 W, respectively, which are available for the application to the 600 MHz DNP-NMR measurement. In addition, this gyrotron can operate at many other frequencies and cavity modes for application to high power THz technologies in wide fields. In this paper, the design and the operation results including long pulse or CW mode are presented.     

Development of second harmonic gyrotrons,Gyrotron FU CW GII and Gyrotron FU CW GIII,equipped with internal mode converters

Second harmonic gyrotrons, Gyrotron FU CW GII and Gyrotron FU CW GIII, were developed at the Research Center for Development of Far-Infrared Region, University of Fukui, Japan to achieve two goals. Each gyrotron was equipped with an internal quasi-optical mode converter. Using Gyrotron FU CW GII allowed the design of the cavity and mode converter to be validated, which was the first goal. After that, Gyrotron FU CW GIII, which is an improved version of Gyrotron FU CW GII, allowed us to achieve a high power output of up to 420 W, which was the second goal, with a cathode voltage setting of ?21 kV and a beam current of 0.57 A. This was achieved using a newly developed electron gun and with the careful sitting of the gyrotron on the magnet.     

Reliability Test of the 170GHz Gyrotron for ITER

Using the ITER relevant 170 GHz gyrotron, repetitive operation with long pulse and high power is conducted. The first consecutive days repetitive operation with ITER equivalent condition (800 kW/600 s with 20 min interval) is successfully performed in JAEA gyrotron test stand in order to obtain a basic data of the reliability of the current gyrotron system. Seventy-two shots out of 88 shots were successfully continued until the end of the pulse (600 s). The successful rate was 82%. The results demonstrate the feasibility of gyrotron operating at a high reliability for high power long pulse operation for ITER like conditions.     

Combined Hyperthermia and Photodynamic Therapy Using a Sub-THz Gyrotron as a Radiation Source

In this paper, we present results of a hyperthermia treatment of malignant tumors using a gyrotron as a radiation source for heating of the cancerous tissue. They clearly demonstrate the efficiency of the irradiation by sub-THz waves, which leads to steady decrease of the volume of the tumor and finally to its disappearance. A combination of hyperthermia and photodynamic therapy (PDT) that utilizes a novel multifunctional photosensitizer has also been explored. In the latter case, the results are even more convincing and promising. In particular, while after a hyperthermia treatment sometimes a regrowth of the tumor is being observed, in the case of combined hyperthermia and PDT such regrowth has never been noticed. Another combined therapy is based on a preheating of the tumor by gyrotron radiation to temperatures lower than the hyperthermia temperature of 43 °C and followed then by PDT. The results show that such combination significantly increases the efficiency of the treatment. We consider this phenomenon as a synergy effect since it is absent when hyperthermia and PDT are applied separately, and manifests itself only when both methods are combined.     

High Frequency and High Mode Purity Operations of Gyrotron FU IVA

The cavity of the newest gyrotron, Gyrotron FU IVA in the high frequency series of Fukui University gyrotrons (the Gyrotron FU series) is designed to minimize the mode conversion from the main cavity mode to the higher modes. In this paper, the experimental results are compared with simulations for the complete gyrotron oscillator. The gyrotron has an additional advantage to cover the wide frequency range in submillimeter wave region.     

Compact Mode Converter System for the Cold Test of Assembled Gyrotrons

A microwave system is described which allows testing of the quasi-optical mode converter in a gyrotron, which is completely assembled except for the attachment of the electron gun. Test results are presented for a TE_6,2,1 gyrotron, and a similar design for a TE_28,7,1 gyrotron is shown.     

紧凑型高阶回旋管模式激励器初步研究

为了模拟回旋管输出的TE62模,需要设计一个模式激励器。文中采用同轴波导谐振腔结构,通过选择合适的内外导体半径比及腔体尺寸,来获得纯度较高的TE62模。并使用HFSS 软件对腔体进行了仿真,仿真计算结果与理论值相吻合,表明这种结构是可行的。     

Theory and Numerical Modeling of a Compact Low-Field High-Frequency Gyrotron

The electron-cyclotron maser interaction provides an extremely efficient means of generating high-power radiation in the millimeter and submillimeter regimes. For devices where both high frequencies and low magnetic fields are required, high cyclotron-harmonic interactions must be considered. We present here a finear and nonlinear analysis of a TE/sub m11/ whispering-gallery-mode gyrotron. Resonances at the mth and (m +- 1)th cyclotron harmonic are found. The start oscillation condition is calculated from linear theory for a wide range of parameters. Maximum efficiency for different beam and cavity conditions is calculated with a fully relativistic numerical simulation code. High efficiencies, >35 percent, have been found at the mth cyclotron harmonic. The effect on the efficiency of an initial velocity spread in the electron beam has also been considered.     

On the Effect of RF-Space Charge on the Beam-Field Interaction in Gyrotrons

The effect of RF-space charge fields on the beam-field interaction in gyrotrons is reviewed. This effect, formerly considered unimportant, is found to cause recognisable differences in simulations of gyrotrons with high current density, such as today’s megawatt level gyrotrons. In this paper, a numerically efficient way of including RF-space charge in the common slow variables model is derived and numerical examples are presented.     

Design of a Compact Sub-Terahertz Gyrotron for Spectroscopic Applications

In this paper we present the initial design of a novel and versatile high frequency gyrotron with parameters suitable for application to various spectroscopic studies that require coherent radiation in the subterahertz frequency range (such as NMR/DNP spectroscopy, ESR spectroscopy, spectrometer based on the X-ray detected magnetic resonance etc.). The most characteristic feature of the design is that it utilises a compact, cryogen-free 8 T superconducting magnet. As a result, the overall dimensions of the entire device are considerably reduced in comparison with the previously developed tubes belonging to the Gyrotron FU and Gyrotron FU CW series. This makes the novel gyrotron highly portable to diverse laboratory environments and easily embeddable to different measuring systems. The electron-optical system (EOS) of the tube is based on a compact low-voltage magnetron injection gun (MIG), which has been specially designed and optimized together with the resonant cavity using our problem-oriented software package GYROSIM for CAD of gyrotrons. The tube operates at the second harmonic of the cyclotron frequency and generates a radiation with an output power of about 100 W and a frequency tunable up to around 424 GHz, respectively.     

一种复合腔回旋管注波互作用的数值模拟和分析

该文基于电磁粒子模拟技术,对一种Ka波段基波渐变复合腔回旋管振荡器的注波互作用过程进行了详细的模拟计算,分析了腔体几何参数、电子注半径、工作电流及工作磁场变化对互作用效率的影响,讨论了工作模式的稳定性。模拟结果表明,适当选择上述参数,在70kV,17A及速度比1.5的电子注推动下,平均功率可达716kW,互作用效率大于60%,且工作稳定。     

Frequency Tunable Gyrotron FU CW VA for Measuring Hyperfine Split of Positronium

New uptapered cavity is designed for the gyrotron FU CW VA enhancing its tunability and enabling its use for measurements of the hyperfine split of positronium.     

Hysteresis in Mode Competition in High Power 170 GHz Gyrotron for ITER

Hysteresis in mode competition in high power 170 GHz gyrotrons for ITER is studied. Specific examples of hysteresis with respect to variation of magnetic field, current, electron beam radius and beam voltage are given.