Radiation structure of single-mode gyrotron

The stationary structure of the radiation field of a gyrotron with an axisymmetric resonator and electron beam is examined. The study is based on the inhomogeneous-string equations for the field and the equation of electron motion for the electron transverse momentum. It is shown that the gyrotron has evanescent modes and modes that travel through the resonator.Institute of Applied Physics, Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 36, No. 1, pp. 88–96, January, 1993.     

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%。     

旋转对称波导型开放式谐振腔的一般理论

本文发展了在电子回旋脉塞中广泛采用的具有旋转对称性的波导型开放式谐振腔的一般理论。理论分析是在截面半径r(z)为任意缓变函数和存在功率输出的最一般情形下进行的,分析了其中场解的形式和性质,导出了谐振频率和Q值的普遍表达式,并以实例说明了实际计算方法。 关键词：     

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.     

Experimental study of a Ka-band gyrotron backward-waveoscillator

A gyrotron backward-wave oscillator (gyro-BWO) has been operated and magnetically tuned over the frequency range 27-32 GHz. Tuning by varying the electron beam voltage was effective over a smaller frequency range (Δf~1 GHz). Output power was as large as 7 kW, corresponding to a device efficiency of 19%. This large efficiency value was unexpected, and related analysis indicates it may be associated with the nonuniform magnetic field profile in the interaction region     

Initial operation of a higher-power quasi-optical gyrotron

Results from the initial operation of a high-power quasi-optical gyrotron based on the 90-kV, 50-A Varian VUW-8144 electron gun are reported. The output power and efficiency have been measured for a resonator mirror separation of 19.4 cm with a magnetic field of 4.95 T, corresponding to resonator output coupling of 1.9%, and for a resonator mirror separation of 21.4 cm with a magnetic field of 4.7 T, corresponding to a resonator output coupling of 3.1%. Operation was multimoded with 3-6 modes excited in the range of 125-130 GHz for the 4.95-T magnetic field. A peak efficiency of 15% at an output power of 161 kW was obtained for a gun voltage of 93 kV and a current of 12 A. A peak-output power of 364 kW at an efficiency of 10% was obtained at a voltage of 95.6 kV and 37.5 A     

Network-theoretical model of the gyrotron oscillator part I: Empty cavity oscillation modes

A network-theoretical model of the gyrotron has been elaborated which is both conspicious and rigorous. The problem of self-consistently representing the field in the presence of the electron beam is attacked by expansion into the empty structure oscillation modes. In this first part, a method is presented to determine the empty gyrotron cavity oscillation modes, i.e. theQ factors, resonance frequencies, and field distributions in axisymmetric, but otherwise quite general cavities. It is based on the field representation in terms of local normal waveguide modes. Matrix equations in these modes for different type of cavity sections (building blocks) are formulated. Along with the open resonator boundary conditions, these equations form a nonstandard eigenvalue problem; the eigenvalues are the complex eigenfrequencies, the eigenvectors correspond to the field distributions. By way of example, the method is applied to a simple and a complex cavity.     

35-GHz 25-kW CW low-voltage third-harmonic gyrotron

A 50-kV third-harmonic gyrotron is shown to be capable of high efficiency. Operation at the third harmonic allows the required magnetic field for 35 GHz generation to be supplied by a 4.5-kG permanent magnet. Two gyrotrons employing sliced circuits for mode control have been evaluated with a large-signal nonself-consistent particle-tracing simulation code and found to be capable of producing 25 kW continuously. The preliminary design of a third-harmonic TE₄₁ gyrotron utilizing a magnetron injection electron gun is predicted to yield a device efficiency of 17%, which can potentially be increased to 46% with an ideal single-stage depressed collector, while an axis-encircling electron beam from a Cusp electron gun is predicted to drive a third-harmonic TE₃₁ gyrotron with a device efficiency of 23%, which can theoretically be increased to 45% through the use of an ideal depressed collector     

A 100 kW, 140 GHz pulsed gyrotron

The design and operation of a 100 kW, 140 GHz pulsed gyrotron are reported. To our knowledge, this is the highest frequency at which high gyrotron output power (>-100 kW) has been achieved. Results are presented for gyrotron operation in the range of magnetic field from 4 to 7 T, voltage from 23 to 80 kV and current up to 7.5 A. Near a value of magnetic field of 5.4 T, and output power of 100 kW was obtained at 140.4 GHz in single mode operation in the TE₀₃₁ resonator mode.     

Numerical Study of Processes in the Cavity of the 170 GHz Gyrotron for ITER Operating at the TE25.10 Mode

The opportunity of use of a TE_25.10 operating mode for CW 170 GHz/1 MW gyrotron for ITER is estimated. Parameters are optimized to achieve maximum efficiency of the gyrotron with an acceptable Ohmic load on the cavity. The influence of unwanted mode conversion at the output of the resonator, mode competition, electron beam potential depression, ion compensation of the space charge and beam energy recovery is investigated.     

Electromagnetic wave generation in a cylindrical resonator by electrons orbiting in a radial electrostatic field

The mechanisms leading to the generation of microwaves by electrons orbiting in a radial electrostatic field produced by a positively charged filament on the axis of a cylindrical resonator are investigated theoretically. The dispersion relations describing the interaction of the waves with the electrons are obtained. It is shown that the generation of electromagnetic fields is possible on account of both Cherenkov and plasma resonances. The frequencies and growth rates of waves under Cherenkov resonance conditions and also plasma resonance conditions in uniform and nonuniform electron layers are found. The advantages and disadvantages of different generation mechanisms are determined. Zh. Tekh. Fiz. 68, 91–94 (August 1998)     

Continuous-Wave Operation of a Frequency-Tunable 460-GHz Second-Harmonic Gyrotron for Enhanced Nuclear Magnetic Resonance

The design, operation, and characterization of a continuous-wave (CW) tunable second-harmonic 460-GHz gyrotron are reported. The gyrotron is intended to be used as a submillimeter-wave source for 700-MHz nuclear magnetic resonance experiments with sensitivity enhanced by dynamic nuclear polarization. The gyrotron operates in the whispering-gallery mode TE(11,2) and has generated 16 W of output power with a 13-kV 100-mA electron beam. The start oscillation current measured over a range of magnetic field values is in good agreement with theoretical start currents obtained from linear theory for successive high-order axial modes TE(11,2,q). The minimum start current is 27 mA. Power and frequency tuning measurements as a function of the electron cyclotron frequency have also been carried out. A smooth frequency tuning range of 1 GHz was obtained for the operating second-harmonic mode either by magnetic field tuning or beam voltage tuning. Long-term CW operation was evaluated during an uninterrupted period of 48 h, where the gyrotron output power and frequency were kept stable to within ±0.7% and ±6 ppm, respectively, by a computerized control system. Proper operation of an internal quasi-optical mode converter implemented to transform the operating whispering-gallery mode to a Gaussian-like beam was also verified. Based on the images of the gyrotron output beam taken with a pyroelectric camera, the Gaussian-like mode content of the output beam was computed to be 92% with an ellipticity of 12%.     

Experimental study of a continuous-wave high-stability second-harmonic gyrotron for spectroscopy of dynamically polarized nuclei

We present the results of the experiments on a continuous-wave gyrotron with an output frequency of about 260 GHz, which has been developed for dynamic polarization of nuclei and is operated at the second cyclotron-frequency harmonic. For an accelerating voltage of 16 kV and a beam current of 0.3 A, a maximum continuous-wave radiation power of about 200 W has been obtained. Measurements of the thermal load on the resonator cavity allow evaluating its actual ohmic Q-factor. Gyrotron radiation is also observed at other frequencies and modes. Their generation zones and the structure of the output radiation have been studied. Long-term stability of gyrotron parameters has been determined.     

会切磁场中大回旋电子束产生的研究

研究了会切磁场产生的机理。通过对Moster-Molnar 模型的探讨, 建立了会切磁场的物理模型。在会切磁场理论分析和数值模拟基础上, 探讨了影响会切磁场设计的因数; 利用拉格朗日公式求解了会切磁场中电子运动轨迹。探讨了会切磁场与大回旋空心会切电子枪的关系, 得到了改进会切电子枪性能的一些一般性结论。     

The spread of the initial energy of electrons in a gyrotron due to the negative-mass instability developing in a magnetron-injector gun

The formation of an electron beam in a magnetron-injector gun of a gyrotron is investigated in the case when it is affected by the negative-mass instability due to the Coulomb repulsion and nonisochronous cyclotron rotation of particles. A technique is proposed for calculating the spread of the initial energy of electrons caused by the instability, which develops as the electron beam moves in the presence of a nonuniform magnetostatic field of the magnetron-injector gun. It is demonstrated that this instability can be one of the main factors providing the energy spread in electron guns of gyrotrons.     

Design and Cold Tests of Asymmetric Quasioptical Resonators

This paper presents the design and test of asymmetric quasioptical resonators for gyrotron applications, where most of the diffraction output coupling comes from the smaller of two mirrors. A computer code based on scalar diffraction theory is used to calculate the resonator losses and the electric field near the mirrors. Resonators with mirror separations approaching confocal have reduced side lobes in the diffraction patterns, which should allow for better power transmission and focusing. Cold tests have been performed at 94 and 141 GHz to measure the quality factor of the asymmetric resonators as a function of mirror separation and mirror misalignment. Typical resonator parameters include 65 cm mirror separation, 1-3% output coupling and 85% of the losses from the small mirror. A half-symmetric resonator with one flat and one curved mirror has also been investigated. The calculated values of Q are in reasonably good agreement with the cold test measurements.     

Enhancement of cavity selectivity in relativistic gyrotrons operated at axisymmetric modes

Mode selection is a key problem from the viewpoint of maintaining the single-mode generation regime in high-power gyrotrons operated at axisymmetric modes. In this paper, we propose several electrodynamic methods of mode selection, which allow separating the electrically strong axisymmetric higher-order mode from spurious modes. The possibility of suppressing the nearest spurious modes efficiently, by using either wide slits in the cavity, or azimuthal corrugations on the walls of the tapered cavity, is shown. A method of mode selection at cyclotron frequency harmonics is proposed. The results of studying two types of gyrotron cavities experimentally at a low power level confirmed their high selective properties. The cavities were calculated aiming at using them as the basis for creation of a gyrotron operated at the TE0.3 mode and producing a power of 5–10 MW in 1 μs long pulses at a wavelength of 1 cm. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 51, No. 10, pp. 837–849, October 2008.     

Nonuniform parametric sound generation in acoustic resonator

A theory of sound generation in an open acoustic resonator excited by a monochromatic sound beam, under nonuniform modulation of the speed of sound in the resonator medium, has been developed. The spectral distribution and temporal profile of the resonator stationary radiation are calculated.     

W波段回旋行波管放大器的模拟与设计

回旋行波管放大器是高功率毫米波雷达发射系统最重要的候选者.通过对回旋行波管放大器中的绝对不稳定性、回旋返波振荡以及电子注-波互作用的研究，讨论了回旋行波管的稳定性、寄生模式的抑制和工作参数的优化等问题，给出了W波段TE₀₁模回旋行波管放大器的模拟设计结果.PIC粒子模拟结果表明，在电子注电压100kV、电流10A、工作磁场3.52T时，94GHz的基波回旋行波管放大器可获得大于250kW的输出功率、40dB的增益、大于25％的效率和约5％的带宽. 关键词： W波段 回旋行波管放大器 模拟 设计