带有反射腔的相对论返波管的数值模拟

 阐述了带有反射腔的相对论返波管的数值模拟研究。利用线性理论[1]设计了返波管的慢波结构，应用SUPERFISH软件设计了谐振反射器。用KARAT软件对谐振反射腔返波管进行了宏观粒子模拟，得到了优化的返波管结构参数，并研究了外加磁场对输出效率的影响。模拟结果表明：谐振反射腔不仅起到截止颈的作用，还有预调制的作用；在低外加磁场条件下，该返波管也能输出较高功率的微波。显示了其在重复频率工作方面的重要意义。     

紧凑型L波段同轴相对论返波振荡器的粒子模拟

 设计了紧凑型L波段同轴相对论返波振荡器，通过粒子模拟研究了L波段同轴相对论返波振荡器相互作用的物理过程，并对器件的电磁结构进行了优化和改进。分析表明，采用同轴慢波结构可以在较低的外加磁场下实现L波段返波振荡器的微波输出，同时可以大大减小微波器件的径向尺寸。这是因为同轴慢波结构的TM01模式有类似于TEM模的性质，没有截止频率，但纵向电场不为零，电子束能够与它发生强相互作用过程。粒子模拟优化结果表明，在器件半径仅为4.0 cm，电子束能量240 keV，电子束流1.8 kA，导引磁场仅为0.75 T时，返波振荡器可以在频率1.60 GHz处获得较大功率的微波输出， 平均峰值功率达140 MW，平均峰值功率效率约为32%。     

带有反射腔的相对论返波管初步实验研究

 阐述了带有反射腔的相对论返波管的初步实验研究进展。反射腔是一段不规则的圆波导,在相对论返波管中起到截止颈的作用。初步实验的结果为：外加磁场B_z =0.82T时,输出微波功率为170MW,微波频率8.874GHz,脉宽为10ns;外加磁场B_z =1.7T时,微波功率为370MW,频率与脉宽不变;根据辐射场功率密度分布判定传输模式为TM₀₁模。结果表明：带有反射腔的返波管在较低外加磁场下也能够工作。     

Relativistic backward wave oscillator using a selective mode converter

A new version of the relativistic backward wave oscillator (BWO) is proposed and investigated experimentally, where the cutoff (for the working mode mode) taper at the cathode end is replaced by a selective Bragg-type mode converter. In the experimental BWO model, which operates in the three-centimeter range and is equipped with a mode converter based on a slightly corrugated waveguide, a radiated power of 700 MW in pulses of duration up to 100 ns with an output spatial structure similar to a Gaussian wave beam is obtained at an accelerating potential of 0.8 MV and a focusing magnetic field of 7 kOe. Zh. Tekh. Fiz. 69, 102–105 (November 1999)     

大功率太赫兹返波管振荡器设计北大核心CSCD

设计了一个过模太赫兹返波管振荡器,通过对慢波结构的精心设计,使电子束动能得到充分提取,实现器件的大功率及高效率运行。在电子能量和束流分别为280keV和320A的条件下,当引导磁场强度为3T时,采用2.5维Particle in Cell(PIC)程序模拟得到频率为121.8GHz、功率为13MW的太赫兹波输出,器件的束波转换效率约为14.5%。     

捷变频相对论返波管振荡器设计

基于低磁场返波管振荡器的工作原理,设计了一个捷变频相对论返波管振荡器,该器件由两段对电子束参数要求基本一致的慢波结构串接而成,通过调节引导磁场强度实现器件频率的调节,使其分别工作于C波段和X波段。在电子能量和束流分别为670keV和8kA的条件下,当引导磁场强度为0.5T时,采用2.5维PIC程序模拟得到频率为6.28GHz、功率为1.0GW的微波输出;而当引导磁场强度为0.8T时,得到频率为9.25GHz、功率为0.75GW的微波输出。     

Pulsewidth limitation in the relativistic backward wave oscillator

Spontaneous pulse shortening occurring in a relativistic backward wave oscillator (BWO) at gigawatt power levels is studied in experiment and theory. It is experimentally demonstrated that this phenomenon is accompanied by formation of an explosive-emission plasma at the surface of the corrugated slow-wave structure (SWS). Termination of microwave emission is explained by the increase of the BWO starting current from the absorption of the operating electromagnetic wave by electrons emitted from the plasma, whereas the intensity of the absorption radically increases offing to the presence of positive ions emitted from the plasma. Application of oil-free vacuum and electrochemical polishing of the SWS surface in an X-band BWO allowed generation of 3-GW, 26-ns microwave pulses with an energy of ~80 J, thereby demonstrating pulse lengthening by a factor of four     

Efficiency enhancement of high power vacuum BWO's using nonuniformslow wave structures

The Sinus-6, a high-power relativistic repetitively-pulsed electron beam accelerator, is used to drive various slow wave structures in a BWO configuration in vacuum. Peak output power of about 550 MW at 9.45 GHz was radiated in an 8-ns pulse. We describe experiments which study the relative efficiencies of microwave generation from a two-stage nonuniform amplitude slow wave structure and its variations without an initial stage. Experimental results are compared with 2.5 D particle-in-cell computer simulations. Our results suggest that prebunching the electron beam in the initial section of the nonuniform BWO results in increased microwave generation efficiency, Furthermore, simulations reveal that, in addition to the backward propagating surface harmonic of the TM₀₁ mode, backward and forward propagating volume harmonics with phase velocity twice that of the surface harmonic play an important role in high-power microwave generation and radiation     

Linear theory of plasma filled backward wave oscillator

An analytical and numerical study of backward wave oscillator (BWO) in linear regime is presented to get an insight into the excitation of electromagnetic waves as a result of the interaction of the relativistic electron beam with a slow wave structure. The effect of background plasma on the BWO instability is also presented.     

过模返波管的正反馈机制

作为一个典型的高功率微波振荡器,过模返波管(backward wave oscillator,BWO)的束波互作用过程复杂,束流负载效应影响明显,但是作为振荡器本身,其本质就是一个正反馈电路,电子从阴极发射后,穿过谐振反射腔和慢波结构(slow-wave structure,SWS),在SWS区电子动能转化为微波能,其中的一部分微波反馈到谐振反射腔,实现对电子束的调制,其他微波通过后面输出端口向外辐射.本文根据这种正反馈机制,建立器件工作模式等效电路和束波互作用的自洽过程,从理论上给出正反馈机制对器件模式控制、起振电流等参数的影响,并模拟研究了这种反馈机制对模式控制的影响,由此设计了一个能够在(1 MV,20 kA)电子束条件下克服模式竞争的过模BWO,其微波输出功率为7.9 GW,频率为8.68 GHz,相应的效率为39.5%.     

3cm相对论返波管的实验研究

简述相对论返波管的基本原理,详细介绍了实验装置与测试方法,报导了初步实验结果,在3cm波段峰值功率约98MW,效率10％左右。     

Relativistic backward wave oscillator with a discrete resonance reflector

We study, both theoretically and experimentally, a relativistic backward wave oscillator BWO with a discrete resonance reflector. It is shown that premodulation of electrons in the reflector region leads to considerable changes in the oscillator characteristics. If a homogeneous slowingdown system (SS) is considered and the space charge is neglected, then the calculated maximum efficiency of oscillation increases from 15% without modulation to 58% in the case of optimal modulation. A pulse-periodic mode of microwave oscillation with pulsed power 0.5 GW at wave-lengths λ≈3 cm was reached in the experiment. Institute for High-Current Electronics, Siberian Branch of the Russian Academy of Sciences, Tomsk, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 42, No. 12, pp. 1189–1196, December, 1999.     

Design of a high-efficiency C-band backward wave oscillator

For practicability of the high power microwave source,a C-band backward wave oscillator(BWO)which has high conversion efficiency is designed.When the axial guiding magnetic field is 0.83 T,the electron energy and the beam current of the diode are respectively 80 keV and 2.1 kA,a microwave output power of100 MW at 7.4 GHz microwave frequency with 65% conversion efficiency is achieved in simulation.     

带谐振腔反射器的低磁场返波管实验研究

 谐振腔反射器到慢波结构输入端之间的漂移段长度对返波管效率有较大影响，文章对该影响进行了理论分析和数值模拟。结果表明：由于谐振腔反射器对电子束的预调制作用，返波管输出功率随漂移段长度的增加而呈现多峰值现象，在选取合适的漂移段长度时，可以显著提高其微波产生的效率。在SINUS－881加速器上开展实验，在引导磁场为0.7 T，漂移段长度为4.9 cm的条件下，实验获得了功率为700 MW，频率为8.7 GHz，脉宽20 ns的微波输出，效率约14%。实验研究证实了模拟结果的正确性。     

Development of a 2 MW relativistic backward wave oscillator

In this paper, a high power relativistic backward wave oscillator (BWO) experiment is reported. A 230 keV, 2 kA, 150 ns relativistic electron beam is generated using a Marx generator. The beam is then injected into a hollow rippled wall metallic cylindrical tube that forms a slow wave structure. The beam is guided using an axial pulsed magnetic field having a peak value 1 T and duration 1 ms. The field is generated by the discharge of a capacitor bank into a solenoidal coil. A synchronization circuit ensures the generation of the electron beam at the instant when the axial magnetic field attains its peak value. The beam interacts with the SWS modes and generates microwaves due to Cherenkov interaction. Estimated power of 2 MW in TM₀₁ mode is observed.      

Theoretical models for designing a 220-GHz folded waveguide backward wave oscillator

In this paper,the basic equations of beam-wave interaction for designing the 220 GHz folded waveguide(FW)backward wave oscillator(BWO) are described.On the whole,these equations are mainly classified into small signal model(SSM),large signal model(LSM),and simplified small signal model(SSSM).Using these linear and nonlinear one-dimensional(1D) models,the oscillation characteristics of the FW BWO of a given configuration of slow wave structure(SWS) can be calculated by numerical iteration algorithm,which is more time efficient than three-dimensional(3D)particle-in-cell(PIC) simulation.The SSSM expressed by analytical formulas is innovatively derived for determining the initial values of the FW SWS conveniently.The dispersion characteristics of the FW are obtained by equivalent circuit analysis.The space charge effect,the end reflection effect,the lossy wall effect,and the relativistic effect are all considered in our models to offer more accurate results.The design process of the FW BWO tube with output power of watt scale in a frequency range between 215 GHz and 225 GHz based on these 1D models is demonstrated.The 3D PIC method is adopted to verify the theoretical design results,which shows that they are in good agreement with each other.     

Dependence of relativistic backward wave oscillator properties oneffective beam gamma

The operation of a backward wave oscillator (BWO) is shown to be critically dependent on the energy of the slow space-charge wave of the electron beam. Experimental work parameterizing the dependence of microwave frequency on effective beam energy, γ_beam, reveals that through an understanding of electron-beam dynamics, a BWO could be systematically tuned through a desired frequency range while maintaining a high power of a few hundred megawatts and narrow frequency bandwidth, which was 400 MHz. Through variation of γ_beam, 1.2 to 1.5 for the experiment, the lack of scaling of peak microwave power with the kinetic energy of the electron beam for γ_beam >1.32 was observed. This effect was previously found in numerical simulation. In order to explain this effect, the relationship of the beam current to the space-charge-limiting current for increasing γ_beam is examined. Dramatic evidence of pulse shortening, a phenomenon known to relativistic oscillators, was also seen     

同轴引出电子束相对论返波振荡器的粒子模拟

 设计了一种L波段同轴引出电子束相对论返波振荡器,采用KARAT 2.5维全电磁粒子模拟程序研究了器件内束-波作用的物理过程,分析了二极管电压和导引磁场对产生微波频率和束-波转换效率的影响。模拟结果表明:该器件在小型化,中等磁场的条件下具有较高的束-波作用效率。在电子束能量700 keV,电子束流10 kA,导引磁场为1.0 T时,器件在频率1.62 GHz处获得较高的微波输出,饱和后微波的平均功率达2.2 GW,平均效率约为30%,器件最大径向半径仅为5.0 cm。     

Study of superradiance based on a low-voltagebackward wave oscillator

According to the small size requirement for wide-band high-power microwave radiation, a superradiance backward wave oscillator (BWO) is proposed to generate such high-power microwave radiation with a low voltage (～20 kV) pulse power supply and low guiding magnet field (～0.1 T). In order to get a high-efficiency C-band superradiance BWO with a low beam voltage and a low guiding magnet field, the mechanism of superradiance in a BWO is explored in particle-in-cell simulation. With the oversized structure, the simulation shows that a microwave power of 405 kW with a frequency of 5.6 GHz and a spectrum width of 500 MHz can be obtained with a voltage of 23 kV and magnetic field of 0.1 T.     

同轴结构多频相对论返波管的粒子模拟

 提出由双电子注同轴相对论返波管产生双频的设想,采用2.5维相对论全电磁PIC粒子模拟软件,进行了粒子模拟研究。结果表明,在环形相对论电子注电压625 kV,电流24 kA,引导磁场0.772 T的条件下,器件得到了稳定的高功率双频微波输出。其双频微波频率分别为11.5,12.2 GHz,两频率相差0.7 GHz,平均功率约为1.15 GW,平均功率效率7.7%。另外,还通过改变周期数,进一步获得了三频的微波输出,并对结果进行了讨论。