Observations of Phase Locking in a Single-Cavity Gyrotron Oscillator

Observations of phase locking in a single-cavity gyrotron oscillator operating at 35 GHz are reported. Injection of the locking power was made via a circulator into the gyrotron output guide. Locking was observed with input power levels as low as 35 dB below the gyrotron power. For low input powers, good agreement is found with theory based on lumped-element circuit modeling and a new distributed oscillator model.     

Phase-locking of a second-harmonic gyrotron oscillator using aquasi-optical circulator to separate injection and output signals

Phase-locking in a 34.5-GHz special complex cavity gyrotron oscillator operating at the second harmonic of the electron cyclotron frequency was studied. Injection of the locking power was made via a quasi-optical circulator connected to the gyrotron output. Locking bandwidth was measured by comparing the phase of the injection signal and output signal using a balanced mixer. Locking was observed with input power level as low as 40 dB below the gyrotron output power. The locking bandwidth is, however, narrower than in gyrotrons operating at the fundamental cyclotron frequency which may be attributed to the longer resonant cavity in the second harmonic gyrotron and the corresponding larger value of external quality factor. The measurements are roughly in agreement with predictions of Adler's phase-locking equation which is given for our system in terms of powers propagating in the output waveguide toward and away from the gyrotron cavity     

连续调谐太赫兹回旋管非稳定振荡状态研究

太赫兹回旋管可实现高功率输出,并具有一定的频率调谐范围,是核磁共振波谱系统理想的高功率太赫兹辐射源。设计了263 GHz,TE_5,2基波连续调谐回旋管,通过磁场调节实现频率调谐范围为1.39 GHz,利用时域多模多频自洽非线性理论对设计的连续调谐回旋管非稳定振荡状态进行了研究。结果表明,在低次纵向谐波模式工作磁场范围内,当工作电流大于起振电流时,连续调谐回旋管先进入稳定状态,高次纵向谐波模式被抑制,工作模式TE_5,2的输出功率随时间不变;当电流增大,纵向谐波模式间的竞争引起回旋管由稳定状态进入到非稳定振荡状态,工作模式TE_5,2的输出功率随时间呈振荡变化且互作用效率大大降低;随着电流的进一步增大,回旋管又回到与低电流不同的稳定状态,互作用效率进一步降低。同时发现非稳定振荡状态的起始电流随着磁场增加而增大。本研究对需工作于稳定状态的面向DNP-NMR应用的连续调谐太赫兹回旋管的研制具有一定指导意义。     

High-power oscillator of continuous electromagnetic radiation with a frequency of 300 GHz

We consider a general concept of construction, the possible versions, and specific features of a gyrotron, whose output power in CW oscillation regime can reach a few kilowatts at a frequency of 300 GHz. The gyrotron is designed for work in a high-frequency facility in combination with a “dry” cryomagnet, which ensures a magnetic field of up to 12 T, required for the gyrotron operation. The basic results of numerical simulation and optimization of the electron gun, the resonant cavity, and other subsystems of the gyrotron are presented. The designs used for the gyrotron development are justified. Preliminary experiments showed the efficiency of the pilotproduction gyrotron with an output power of about 2 kW, which is record-breaking in this frequency range. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 50, No. 6, pp. 461–470, June 2007.     

Efficient Low-Voltage Operation of a CW Gyrotron Oscillator at 233 GHz

The gyrotron oscillator is a source of high average power millimeter-wave through terahertz radiation. In this paper, we report low beam power and high-efficiency operation of a tunable gyrotron oscillator at 233 GHz. The low-voltage operating mode provides a path to further miniaturization of the gyrotron through reduction in the size of the electron gun, power supply, collector, and cooling system, which will benefit industrial and scientific applications requiring portability. Detailed studies of low-voltage operation in the TE(2) (,) (3) (,) (1) mode reveal that the mode can be excited with less than 7 W of beam power at 3.5 kV. During CW operation with 3.5-kV beam voltage and 50-mA beam current, the gyrotron generates 12 W of RF power at 233.2 GHz. The EGUN electron optics code describes the low-voltage operation of the electron gun. Using gun-operating parameters derived from EGUN simulations, we show that a linear theory adequately predicts the low experimental starting currents.     

特殊三反射镜太赫兹波段准光腔回旋管的动力学理论

基于回旋管线性理论,运用Laplace变换和留数定理的方法,在线性Vlasov-Maxwell方程组的框架下,研究了特殊三反射镜准光腔回旋管的动力学理论.导出了注-波互作用功率、频偏和起振电流公式,运用MATLAB进行了数值运算.结果表明,这种回旋管工作于高次谐波状况下能有较高的互作用功率,具有工作于太赫兹波段的潜力. 关键词： 三反射镜准光腔 太赫兹 回旋动力学理论     

Possible operation of a 1.5-2-MW, CW conventional cavity gyrotron at 140 GHz

We present a study of the feasibility of continuous wave (CW) operation of a 140-GHz conventional cavity gyrotron at high power levels operating in the TE/sub 31,8/- and TE/sub 25,10/-modes. The question of mode selection is discussed, and a possible design of such a gyrotron with beam energy up to 90 keV and a current of 60-70 A is given. We find that it should be possible to operate a 140-GHz gyrotron at power up to 2 MW if a sufficiently high-order mode is used, although CW power may be somewhat lower.     

Startup and mode competition in a 150 GHz gyrotron

Conclusion The startup of a gyrotron with a tapered resonator section operating at 150 GHz in the TE03-mode has been investigated with special emphasis on mode competition. Calculations show that multimoding occurs only for high currents and a small range of magnetic field strengths. Thus pure TE03 operation with powers exceeding 200 kW seems to be possible for tapered resonatorsThe pulse shape of the power supplies has a great influence on the startup of the gyrotron, and should therefore always be considered in the study of mode competition.To better predict experiments gyrotron theory should be self-consistent. Recent work at the KfK [14] shows progress in this field. For the above diagrams some quantitative changes are expected, but the two main results of this work on multimoding and the influence of the power supply will remain valid. Experiments on the gyrotron, which started recently should confirm the predictions and give impulses for further developments in gyrotron theory.     

95 GHz三次谐波回旋管设计

采用线性理论和非线性理论研究了回旋管谐振腔结构、寄生模式抑制及注波互作用等问题。设计了一支工作在95 GHz的三次谐波回旋管,注波互作用结构采用标准开放式谐振单腔,工作模式为TE64, 采用电压45 kV、电流5 A、横纵速度比为1.5的小回旋电子注。在不考虑电子注速度离散及厚度的情况下,非线性理论分析表明,该回旋管可以获得14 kW功率输出,横向互作用效率约为18%,整管效率约11%。     

Continuous-Wave Operation of a 460-GHz Second Harmonic Gyrotron Oscillator

We report the regulated continuous-wave (CW) operation of a second harmonic gyrotron oscillator at output power levels of over 8 W (12.4 kV and 135 mA beam voltage and current) in the TE(0,6,1) mode near 460 GHz. The gyrotron also operates in the second harmonic TE(2,6,1) mode at 456 GHz and in the TE(2,3,1) fundamental mode at 233 GHz. CW operation was demonstrated for a one-hour period in the TE(0,6,1) mode with better than 1% power stability, where the power was regulated using feedback control. Nonlinear simulations of the gyrotron operation agree with the experimentally measured output power and radio-frequency (RF) efficiency when cavity ohmic losses are included in the analysis. The output radiation pattern was measured using a pyroelectric camera and is highly Gaussian, with an ellipticity of 4%. The 460-GHz gyrotron will serve as a millimeter-wave source for sensitivity-enhanced nuclear magnetic resonance (dynamic nuclear polarization) experiments at a magnetic field of 16.4 T.     

Comparison of Electron-Beam-Misalignment Effect on Starting Current and Output Power in Coaxial-Cavity and Cylindrical-Cavity Gyrotron Oscillators

Comparative study is presented to the effect of the electron-beam misalignment on the starting current and output power of the coaxial-cavity and cylindrical-cavity gyrotron oscillators operating in the millimeter wave ranges. The numerical analysis is based on the gyrokinetic formulas for a TE_28,16,1 mode at a frequency of 140 GHz. Results show that the coaxial-cavity gyrotron oscillator has lower starting current and less power loss than the cylindrical-cavity gyrotron oscillator when the electron-beam axis has a misalignment to the cavity axis.     

D-band frequency step-tuning of A 1 MW gyrotron using a brewster output window

In order to demonstrate the usability of gyrotron oscillators as frequency step tunable high power millimeter-wave sources, experiments on a 1 MW, 140 GHz TE_22,6 gyrotron with a built-in quasi-optical (q. o.) mode converter have been performed. By varying the operating parameters of the tube, a series of oscillations in the frequency range from 114 GHz to 166 GHz were excited. To avoid reflections, caused by the required vacuum barrier window, the gyrotron was equipped with a Brewster window. The achieved output power levels between 0.85 and 1.05 MW are compared to measurements carried out with the same tube using a conventional single-disk window. These experiments showed that even by using a q. o. mode converter, the influence of window reflections on the gyrotron oscillatory behavior cannot be removed completely.     

105/140 GHz双频兆瓦回旋管实现1.0 MW脉冲输出

报道了聚变应用的MW级双频（105/140 GHz）回旋管的最新实验进展。该回旋管的谐振腔、准光模式变换器、输出窗采用了双频共用的设计,电子枪采用了双频复用的双阳极磁控注入枪,收集极采用单极降压。最新的实验表明:在重频1 Hz短脉冲条件下,在105 GHz点和140 GHz点,测试得到脉冲功率分别为710 kW和1.057 MW,对应总效率分别为34%和49%。这是国内首次在回旋管实验中实现1.0 MW功率输出。     

Conditioning optics for astigmatic gaussian beams at 140 GHz, 0.5 MW

A quasi optical system was designed to couple the RF power coming from a gyrotron with astigmatic gaussian beam output into a transmission line consisting of an oversized corrugated waveguide. The gyrotron is capable of delivering500 KW at140 GHz for0.5 s. The whole system is described together with low power tests on parts of it.     

Experimental investigation of a 140-GHz coaxial gyrotron oscillator

We report experimental results on a megawatt power level, 140-GHz coaxial gyrotron oscillator. The gyrotron has an inverted magnetron injection gun (IMIG) designed for operation at up to 95 kV and 88 A. The IMIG has an inner grounded anode which extends from the center of the gun down through the entire length of the tube including the cavity and collector. The IMIG was tested at up to 105 kV and 93 A in 3 μs pulses, achieving an electron beam power of 10 MW. The output power from the coaxial gyrotron cavity was transported to an internal mode converter and a single mirror that coupled the power out transversely from the tube axis. A maximum output power of up to 1 MW was obtained in the TE_27,11 mode at 142 GHz at an efficiency of 16%, about one half of the design efficiency. The reduced efficiency was attributed to nonuniformity of the cathode emission and the sensitivity to the relative alignment of the electron gun, coaxial insert, and cavity. The cathode emission over the azimuthal angle was measured for two cathodes and was shown to be nonuniform due to both temperature and emitter work function nonuniformity. The gyrotron was also tested in two alternate configurations: 1) with the internal mode converter removed (axial output), and 2) with both the internal converter and the coaxial insert removed (empty cavity). In operation in the empty cavity configuration, which is equivalent to a conventional gyrotron oscillator, output power of up to 0.9 MW was observed     

W波段连续波30 kW回旋振荡管高频系统和收集极的设计

 根据回旋管的电子回旋脉塞理论,借助于编写的回旋振荡管自洽非线性注-波互作用计算程序,设计出了工作频率94 GHz、工作电压30 kV、工作电流3 A的基次谐波连续波单腔回旋振荡管,工作模式为TE02模。设计的回旋振荡管在电压30.0 kV、电流3.0 A、速度横纵比1.5的条件下,获得了31.8 kW的输出功率,电子效率约35％。利用粒子模拟仿真软件对设计的回旋管收集极辅助线包散焦系统进行了粒子模拟仿真分析,模拟结果表明：借助于辅助线包散焦系统可以有效缩短回旋振荡管的轴向尺寸,并使回旋管收集极上的电子束功率密度低于500 W/cm2; W波段回旋振荡管收集极的热测试验结果表明：利用粒子模拟仿真获得的收集极上的电子束功率密度分布与其试验测量结果比较吻合。     

Temporal Dynamics of Mode Interaction in Submillimeter-Wave Second-Harmonic Gyrotron

Competition of the operating modes at the second cyclotron harmonic with spurious modes at fundamental is studied numerically for the cases of gyrotron and traveling opposite spurious modes in the gyrotron FU II. This competition limits significantly the output power at the second harmonic. The results are in good agreement with experiments.     

全三维110GHz和220GHz同轴腔双注回旋管数值模拟研究

为了打破传统单注回旋管只能产生较低功率的局限性, 本文基于自主研发的PIC粒子模拟软件CHIPIC 对110 GHz和220 GHz同轴腔双注回旋管进行全三维数值模拟研究. 在理论分析同轴双电子注电子枪设计模型和初始参数的基础上通过CHIPIC对其进行优化设计, 得到了具有横纵速度比为1.0, 最大速度零散约为5.4%的高性能电子束; 并将此优化后的双阳极双注电子枪取代传统回旋管数值模拟时采用的回旋 发射进行110 GHz和220 GHz双注回旋管整管的数值模拟, 并采用MPI四进程并行计算, 最终获得了具有双频分别为110 GHz和220 GHz、模式为TE₀₂模、平均输出功率约在70 kW、 效率达到8.75%的高性能双注回旋振荡管. 关键词： 同轴腔双注回旋管 同轴双电子注电子枪 横纵速度比 速度零散     

The gyrotron: Constraints on output-power and efficiency increase

With allowance for the results of national and foreign gyrotron developments, we analyze constraints on the gyrotron efficiency and output power stipulated by the properties of the electron beam, the processes in a resonant cavity, the output-window throughput, the scattered-radiation losses in a built-in converter, and the energy release on a collector. A comparative estimate of the influence of the factors limiting the gyrotron power and efficiency is given. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 49, No. 10, pp. 864–871, October 2006.     

Specific features of the development of a high-stability continuous-wave gyrotron operated at the second harmonicwith a working frequency OF 258 GHz

We consider specific features of the development of a continuous-wave 258 GHz gyrotron operated at the second gyrofrequency harmonic, which are related to ensuring of high stability of its output parameters. The requirements to accuracy of manufacture of the cavity and adjustment of the electron beam are evaluated, as well as the necessary parameters of the power sources of the gyrotron complex, which should maintain the required level and stability of the generated power and frequency. The influence of the effect of spurious-mode reflection from the output window of the gyrotron is studied.