Large-signal theory of gyro traveling wave tubes at cyclotronharmonics

A nonlinear theory of gyrotron traveling wave tubes (gyro-TWTs) at cyclotron harmonics has been developed taking into account the electron velocity spread and the possibility of operating with significant Doppler frequency up-shift (CARM operation). It is shown that the orbital efficiency of the relativistic gyro-TWT operating at the second cyclotron harmonic with large frequency up-conversion may exceed 60%. It is also shown that the influence of the axial inhomogeneity of the wave field on the relation between amplitudes of electric and magnetic fields of the wave causes small changes in the efficiency of gyro-TWTs. The results obtained demonstrate the sensitivity of the harmonic gyro-TWT efficiency with respect to electron velocity spread at different axial wave numbers. The expressions for the gain are derived and discussed,     

High-power harmonic gyro-TWT's. II. Nonlinear theory and design

For pt.I, see ibid., vol.20, no.3, p.155-162 (1992). Based on an analytical study of the stability problems of gyrotron traveling wave amplifiers (gyro-TWTs), an extremely high power second-harmonic gyro-TWT has been designed, evaluated and optimized with a self-consistent nonlinear numerical simulation code. The design, which is based on the magnetron-injection-gun (MIG)-type beam, is presented. Using a 100 kV, 25 A MIG beam with α=1 and an axial velocity spread of 5%, nonlinear self-consistent analysis of a three-stage second-harmonic gyro-TWT amplifier predicts a peak output power of 533 kW, peak efficiency of 21.3% and a 7.4% saturated bandwidth, which verifies the theoretical predictions that a stable harmonic gyro-TWT can generate power levels an order of magnitude higher than those possible from a fundamental gyro-TWT. It is shown that the positioning of the electron beam is very important. A multistage structure is used to recover the loss in gain resulting from shortening the interaction sections to ensure stability     

ELECTRON BUNCHING CHARACTERISTICS IN THE GYROTRON TRAVELING-WAVE AMPLIFIER WITH TWO-STAGE INTERACTION CIRCUIT

Based on a simplified model, an analytic theory describing the bunching of the electron beam in a gyrotron traveling wave tube (gyro-TWT) with two-stage interaction circuit is presented. The analytic formulas of the traveling-wave bunching parameter, ballistic bunching parameter, and the density of the bunching beam are obtained. The bunching procedures corresponding to different harmonic operations are studied. It is shown that the maximum of harmonic component depends on the ratio of the harmonic number in the output stage to that in the input stage, not on their absolute values.     

基于损耗介质加载波导的回旋行波管放大器的互作用分析

损耗介质波导对提高回旋行波管放大器的稳定性等性能具有积极的作用.本文基于损耗介质波导中工作模式的场表达式,推导出电子回旋脉塞互作用线性理论.通过系统的数值计算发现损耗介质波导与光滑金属圆波导中的工作模式从场型分布和色散关系上都具有一一对应关系;通过Laplace变换,利用互作用线性理论计算工作模式的起振场型和阈值,并研究互作用系统磁场、电流和介质层对放大特性的影响.这些研究成果对促进损耗介质在回旋行波管放大器中的运用和高稳定性回旋行波管放大器的发展具有积极的作用.     

Geometrical Effects on the Performance of Coaxial-Waveguide Gyrotron Traveling-Wave Amplifiers

This theoretical investigation examines the feasibility of improving the stability of the coaxial-waveguide gyrotron traveling-wave tube (gyro-TWT) by selecting the geometrical parameter C, i.e., the ratio of the outer radius to the inner radius. The effects of the geometrical parameter C on the start-oscillation currents of oscillation modes are analyzed to determine the optimum operating conditions. Simulation results indicate that the coaxial gyro-TWT with distributed wall losses can be stably operated at a higher beam current by optimizing C. Additionally, the saturated behaviors of the operating TE₀₁ mode are evaluated for several C values to investigate the geometrical effects on the amplification of the coaxial gyro-TWT. Moreover, performance of the fundamental harmonic coaxial gyro-TWT achieved with the optimized C value is predicted under stable operating conditions.     

大回旋cusp电子注数值模拟

 新一代宽带、高增益、大功率回旋行波管需要新型的电子注，而大回旋cusp电子注为其实现提供了可能。对大回旋cusp电子注进行系统理论分析，建立了大回旋cusp电子注的物理模型，在理论分析基础上进行了大量数值计算和模拟优化，并对大回旋cusp电子枪设计中的影响因素进行探讨。设计出一支低速度零散、高速度比、低纹波，适用于高次谐波的高功率(54 kV, 2.7 A)cusp电子枪。     

Ka波段二次谐波损耗波导回旋行波管非线性分析

 建立了由损耗段和铜段组成的波导结构的Ka波段二次谐波回旋行波放大器理论模型,并进行了非线性理论研究。基于稳定性分析,确定35 GHz TE₀₂模二次谐波回旋行波放大器的基本工作参数:波导半径为1.02 cm,电子注工作电压为90 kV,工作电流为25 A,工作磁场为0.642 6 T,横纵速度比为1.2;然后通过模拟详细分析了工作电流、波导损耗和速度零散等因素对该放大器性能的影响。研究表明：在该结构中损耗段可以有效地抑制模式竞争从而提高输出功率和带宽;工作电流对输出功率的影响存在最大值;速度零散对输出功率有很大的影响。     

W-Band Second-Harmonic Gyrotron Traveling Wave Amplifier with Distributed-Loss and Severed Structures

The second harmonic TE₀₂ gyrotron traveling wave amplifier (gyro-TWT) is a high-power, broadband, millimeter-wave amplifier with a low applied magnetic field. Mode-selective interaction circuits were applied to suppressing spurious oscillations. However, the mode-selective interaction circuit may perturb the operating mode in the gyro-TWT. A multi-stage gyro-TWT design with distributed-loss and severed structures is proposed to stabilize the amplification. This study presents a nonlinear analysis of typical oscillations, including absolute instability, gyrotron backward oscillation (gyro-BWO) and reflective oscillation. The lossy and severed sections of the multi-stage gyro-TWT seem to increase effectively the start-oscillation currents of the absolute instability, gyro-BWO, and reflection oscillation. The multi-stage gyro-TWT is predicted to yield a peak output power of 215 kW at 89.9 GHz with an efficiency of 14.3 %, a saturated gain of 60 dB and a bandwidth of 1.7 GHz for a 100 kV, 15 A electron beam with an axial velocity spread _z/ _z = 5%.     

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%。     

Ka波段螺旋波纹波导回旋行波管

螺旋波纹波导回旋行波管与采用圆波导的回旋行波管相比,有较大的带宽。介绍了它的线性注波互作用理论,并用该理论计算了不同的磁场与波导表面微扰幅度对Ka波段螺旋波纹波导回旋行波管线性增益的影响。计算结果与已报道的实验结果基本符合,说明该理论可以初步确定螺旋波纹波导回旋行波管的各项参数。     

光子带隙谐振腔回旋管振荡器的自洽非线性理论

定义了光子带隙谐振腔(photonic-band-gap cavity, PBGC)的等效半径,论证了使用该半径将PBGC等效为具有模式选择性的金属圆柱谐振腔的有效性,揭示了其在PBGC设计过程中的指导性作用.基于等效半径的运用,建立起光子带隙谐振腔回旋管振荡器(PBG回旋管)的自洽非线性理论,并对工作于TE₃₂模的PBG回旋管作了理论分析和数值计算.目前的研究表明:高频电磁场沿角向呈行波或驻波的不同极化形式对PBG回旋管的注-波互作用过程具有较大的影响;较之电子回旋基波,该器件中二 关键词： 光子带隙谐振腔 等效半径 回旋管 自洽非线性理论     

Studies of a Gyrotron Traveling-Wave Tube with Helically Corrugated Waveguides at IAP Ras: Results and Prospects

Radiophysics and Quantum Electronics - The gyrotron traveling-wave tube (gyro-TWT) is a wideband version of gyrotron amplifiers, which produce pulsed or continuous-wave radiation in the...     

Q波段回旋行波管新型盒型输出窗的设计

利用等效电路理论,初步设计了窗片厚度为1.32mm的回旋行波管盒型输出窗,再加入感性膜片,更改窗片形状,最终设计出了能承受25kW平均功率、相对带宽达到14%、窗片厚度达到1.7mm的Q波段新型宽频带回旋行波管盒型输出窗;采用高频软件HFSS与有限元分析软件ANSYS协同仿真的新方法对回旋行波管盒型窗进行热特性研究表明,盒型窗理论上功率容量达到62kW平均功率,说明输出窗窗片承受25kW平均功率的可行性,窗片中心与边缘的温差为66℃,没有达到陶瓷窗片的临界温差158℃,验证了新型盒型窗设计的合理性。     

Periodicity-suppressing effect of periodic lossy-dielectric-loaded cylindrical waveguide

Periodic dielectric-loaded waveguide is one of the diaphragmatic waveguides.For the excellent mode-selective propagation ability,it is of value for applications in gyrotron-traveling-wave amplifiers(gyro-TWT),accelerators,and other microwave propagation systems.This paper focuses on studying the application of the strong lossy-dielectricloaded periodic waveguide in millimeter-wave gyro-TWT.It is revealed that due to the lossy property of the dielectric,the energy in the dielectric slots is absorbed effectively and the high order Bloch harmonics induced by the periodicity of the structure are suppressed,which changes the discrete spectrum under lossless condition into a continuous one.As a result,the periodicity of the system is severely suppressed and a mode in the hollow region could be approximated by a fast wave mode in an empty waveguide.These results bring specific guidance for the applications of the lossy dielectric-loaded waveguide in gyro-TWTs and other devices.     

Theory and experiment of ultrahigh-gain gyrotron traveling waveamplifier

Physics and technology issues of importance to the high-gain gyrotron traveling wave amplifier (gyro-TWT) are investigated in theory and experiment. The gyro-TWT is known to be highly susceptible to spurious oscillations, especially in high gain operations. In the current study, oscillations of various origins are classified and characterized with detailed theoretical modeling. They are shown to be intricately connected to the interplay between the absolute/convective instabilities, circuit losses, and reflective feedback. Knowledge of these processes leads to the concept of an ultra high gain scheme which employs distributed wall losses for the suppression of spurious oscillations. A proof-of-principle Ka-band gyro-TWT experiment stable at zero drive has produced 93 kW saturated peak power at 26.5% efficiency and 70 dB gain, with a 3 dB saturated output power bandwidth of 3 GHz. The saturated gain is more than 30 dB beyond that previously achieved     

Stability of a 95-GHz slotted third-harmonic gyro-TWT amplifier

A low-magnetic-field moderate-voltage gyrotron amplifier has been designed for stable high-performance operation at 95 GHz. A slotted interaction circuit is utilized to achieve strong amplification near the third cyclotron harmonic frequency. The start-oscillation conditions were determined by an analytical theory and confirmed by a multimode particle-in cell simulation code. The dominant threat to the amplifier's stability is from a third-harmonic peniotron backward-wave interaction. A slow-timescale particle-tracing simulation code predicts the three-section slotted third-harmonic gyro-TWT, which utilizes an 11.6-kG magnet and a 50-kV 3-A υ_⊥/υ_z=1.4 axis-encircling electron beam with an axial velocity spread of 6% will yield an output power of 30 kW with an efficiency of 20%, a saturated gain of 40 dB, and a constant-drive bandwidth of 2%     

Nonlinear Analysis of A Slotted Third-Harmonic Gyro-TWT Amplifier

The distribution of RF field of the slotted cylindrincal waveguide is discussed and the self-consistent nonlinear theory of the beam-wave interaction is presented in this paper.The behavior of the 95-GHz slotted third-harmonic gyrotron traveling-wave amplifier (gyro-TWT) with a uniform section is simulated by a Runge-Kutta algorithm code for an axis-encircling electron beam with velocity spread. Some important relations in the process of the beam-wave interaction are abtained and analyzed.     

分布损耗加载回旋行波管多模稳态注波互作用理论与比较证实

基于目前国际上实验研究的均匀介质加载和周期介质加载结构,建立了一种分布式损耗加载回旋行波管(gyro-TWT)多模稳态注波互作用理论.利用这一理论,以TE01模式基波gyro-TWT注波互作用为例,将Ka和W波段的理论结果与实验和软件仿真进行比较,以证实理论的合理性.     

Amplification of picosecond pulses in a 140-GHz gyrotron-traveling wave tube

An experimental study of picosecond pulse amplification in a gyrotron-traveling wave tube (gyro-TWT) has been carried out. The gyro-TWT operates with 30 dB of small signal gain near 140 GHz in the HE?? mode of a confocal waveguide. Picosecond pulses show broadening and transit time delay due to two distinct effects: the frequency dependence of the group velocity near cutoff and gain narrowing by the finite gain bandwidth of 1.2 GHz. Experimental results taken over a wide range of parameters show good agreement with a theoretical model in the small signal gain regime. These results show that in order to limit the pulse broadening effect in gyrotron amplifiers, it is crucial to both choose an operating frequency at least several percent above the cutoff of the waveguide circuit and operate at the center of the gain spectrum with sufficient gain bandwidth.     

Design and Simulation of an Ultra-Broadband Ku-BandGyro-TWT for Radar Applications

In this paper, the design of an ultra-broadband Ku-band gyro-TWT amplifier is presented in detail. The preliminary parameters of the interaction structure derived from the dispersion relationship and the linear theory of the gyro-TWT with distributed wall losses is optimized by the self-consistent nonlinear code. The performance of the designed gyro-TWT is simulated by the nonlinear code. The simulation results show that the gain and the bandwidth of the designed Ku-band gyro-TWT is about 36.5 dB and 2.1 GHz with 3 dB bandwidth (about 12.7%) respectively at the input power 19.0 W.