Dependence of Output Power on Cavity Length in a Gyrotron Backward Wave Oscillator

A relativistic electron beam (500 keV, 200 A, 10 ns) generated magnetically tunable microwave radiation in a frequency range of 9-13 GHz when it is injected into an X-band rectangular waveguide immersed in a uniform axial magnetic field (4-10 kG). The mechanism of the microwave radiation was identified as the gyrotron backward wave interaction. The output power of the radiated microwave increased exponentially with the increase of the cavity length.     

Gyrotron Backward Wave Oscillator Experiments with a Relativistic Electron Beam Using an X-Band Rectangular Waveguide

A mildly relativistic electron beam (500keV, 200A, 10ns) injected into an X-band rectangular waveguide immersed in a uniform axial magnetic field (4-10kG) produced magnetically tunable microwave radiation in the 9-13 GHz frequency range with an estimated output power of 1MW. The frequency range and tunability of the radiated microwave agreed with a theoretical model for a gyrotron backward wave oscillator taking into account the low energy component of the beam electron.     

Research of sine waveguide slow-wave structure for a 220-GHz backward wave oscillator

A watt-class backward wave oscillator is proposed,using the concise sine waveguide slow-wave structure combined with a pencil electron beam to operate at 220 GHz.Firstly,the dispersion curve of the sine waveguide is calculated,then,the oscillation frequency and operating voltage of the device are predicted and the circuit transmission loss is calculated.Finally,the particle-in-cell simulation method is used to forecast its radiation performance.The results show that this novel backward wave oscillator can produce over 1-W continuous wave power output in a frequency range from 210 GHz to 230 GHz.Therefore,it will be considered as a very promising high-power millimeter-wave to terahertz-wave radiation source.     

A high power microwave vircator with an enhanced efficiency

A radially extracted vircator (virtual-cathode oscillator) with two identical opposite output ports is presented. The microwave modes propagating inside the WR650 output rectangular waveguide are determined by the calibrated E-probes lined up in the direction perpendicular to the axis of the WR650 waveguide. Velvet-covered cathodes are used to emit electrons. Several diameters of velvet are chosen to see how the emitting area effects microwave generation. Evidence of virtual cathode formation, onset of electron reflexing, and simultaneous microwave emission are discussed. This vircator is found to have the capability of generating a maximum 1.4 GW microwave pulse with the dominant frequency at 8.2 GHz. The radiation pattern is dominated by the TE₁₀ mode and the instantaneous efficiency for producing this microwave pulse is around 6±0.8%. Simple E-probes are applied to pick up the microwave signals inside the WR650 output rectangular waveguide     

Ultrafast photodetectors based on the interaction of microwave radiation and a photoexcited plasma in semiconductors

The interaction of microwave radiation with the plasma in photoionized semiconductor photocells (CdS, CdSe) placed in waveguide measurement systems is investigated theoretically and experimentally. The interaction of the characteristic waveguide modes with a photoexcited semiconductor plasma is investigated. The dependence of the reflection coefficient and phase of the microwave radiation on the intensity of the optical radiation to be measured is obtained, and the influence of the surface of the semiconductor photocells on these parameters is investigated. A microwave photodetector design based on a millimeter-wave interferometer is developed. Zh. Tekh. Fiz. 68, 94–98 (November 1998)     

Measurements of broad-band millimeter-wave radiation from anIREB-plasma interaction system

High-power broad-band millimeter-wave radiation is emitted from a plasma in a strong Langmuir turbulence state driven by an intense relativistic electron beam. We measured directivity and spectrum of this radiation with a filter-bank spectrometer, a heterodyne spectrometer, and a filter-waveguide-combination spectrometer covering 18-140 GHz. The directivity measurement indicated that the radiation was relativistically beamed. The observed spectra were nearly flat up to about 40 GHz and declined steeply above 40 GHz. Discussion is given on the experimental results in connection with the collective Compton boosting model proposed by Benford and Weatherall (1992)     

Microwave pulse shortening in plasma relativistic high-current microwave electronics

We describe mechanisms of microwave pulse shortening in radiation sources with the power of about 10⁸ W based on interaction between relativistic electron beams of nanosecond duration and preformed plasma. The shortening is mainly due to the electron return flow through the plasma, which leads to a multiple decrease in the linear gain of the microwave by the relativistic electron beam and in the reflection coefficient of the plasma wave that provides the generator feedback. The ways to eliminate the effect of microwave pulse shortening are proposed.     

X波段重频过模返波振荡器实验研究

根据两腔振荡器和返波管的特点研制了过模结构返波振荡器, 该器件主要由调制腔和换能腔(慢波结构)两部分组成. 调制腔既是电子束的预调制腔, 也是微波谐振反射腔, 它同换能腔形成一个过模微波谐振腔,经调制腔调制后的电子束在换能腔中实现束波能量转换. 根据加速器的电子束参数(束压为1 MV,束流为20 kA)设计了一个X波段的高功率微波器件,2.5维粒子模拟程序模拟得到微波频率为8.25 GHz,输出功率为5.70 GW. 用超导磁体作为引导磁场,单次运行输出微波功率为5.20 GW,微波频率为(8.25±0. 关键词： 两腔振荡器 返波振荡器 多波切连科夫发生器     

Super-reltron theory and experiments

A highly efficient, high-power microwave tube called super-reltron is reported. The authors have achieved operation at >400 MW with ~50% efficiency at 1 GHz, and 250 MW with 40% efficiency at 3 GHz. The RF pulse durations are typically a few hundred nanoseconds. These compact lightweight tubes do not require an external magnetic field. The RF output coupling is straightforward and delivers the power directly via the fundamental TE₁₀ wave in a rectangular waveguide without a mode converter. The key features of the tube include (i) generation of a well-modulated electron beam by periodic virtual cathode formation, (ii) postacceleration of the modulated beam to reduce the relative electron energy spread, and (iii) a multicavity output section that efficiently extracts power without RF breakdown. Various theoretical aspects of the device are discussed and the experimental results are summarized     

双波段相对论返波振荡器模拟研究

 提出了一种采用单电子束实现C波段和X波段微波同时输出的新型相对论返波振荡器,该器件的束波作用区为中间用渐变段隔开的两段盘荷结构。使用Karat软件进行了2.5维全电磁粒子数值模拟,在工作电压为1 MV,电流为8 kA,导引磁场为3 T的条件下,输出微波功率大于1 GW,功率效率约为15%,输出的微波频率分别为5.42 GHz和9.58 GHz,二者频谱幅度相差2.17 dB,模式为TEM模。     

Cyclotron superradiance of a high-current electron bunch under group synchronism conditions

We have theoretically and experimentally investigated the process of induced coherent emission (superradiance) in an electron bunch rotating in a homogeneous magnetic field. We have shown that this process makes it possible to generate ultrashort microwave pulses. In this case, the optimum conditions are found under group synchronism conditions, when the translational velocity of the bunch matches the group velocity of the radiation propagating in the waveguide circuit. For experimental investigation of the superradiance, we used a RADAN accelerator with subnanosecond electron pulse sharpener. In the 35 GHz range, we obtained microwave pulses with record short duration, down to 0.4 nsec for a peak power level up to 200 kW. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 89–97, December, 1996.     

单电子束双波段同轴相对论返波管粒子模拟

设计了一种能在C波段和X波段实现稳定双频输出的带有非对称谐振反射腔的单电子束同轴相对论返波振荡器。采用耦合阻抗跃变型慢波结构,使用粒子PIC模拟软件进行了粒子模拟研究。模拟结果显示:轴向电场在系统中的分布得到改进,电子束的能散得到改善。在电子束电压511 kV,电流8.95 kA,引导磁场0.73 T的条件下,双频器件实现了8.09 GHz和9.91 GHz的双波段频率稳定输出,平均功率为1.0 GW,波束互作用效率为21.9%, 效率高于空心双波段返波管及其他双波段器件。器件辐射功率的拍频为1.82 GHz,拍波更为明显和稳定。模拟研究中同时发现, 随着慢波结构之间漂移段的变化,双频频率都呈现一种准周期的变化。     

X波段重复频率GW级超辐射相对论返波管

运用超辐射机理,通过粒子模拟设计了X波段超辐射相对论返波管,并在小型Tesla脉冲源平台上开展了实验研究。通过空间功率积分和直接对辐射微波时域波形的分析得到实验结果:在束压350 kV、束流4.8 kA、脉宽3.1 ns、引导磁场2.2 T条件下,产生的微波辐射功率1.4 GW,中心频率9.36 GHz,脉宽500~700 ps,辐射模式为TE11,能在重复频率100 Hz下稳定运行。功率转换效率超过80%。实验结果与粒子模拟结果比较吻合,成功实现了在短脉冲条件下产生重复频率、亚纳秒脉宽、GW级微波辐射。     

Microwave emission and beam propagation measurements in ahigh-power relativistic electron beam-plasma system

Microwave emission was measured from a system consisting of an unmagnetized plasma and a propagating electron beam. A 93-cm² velvet cathode, with an anode-cathode gap of 5.9 cm, injects the electron current into the plasma through an aluminized Mylar anode. Measurements were made of the diode voltage and current in the 6-μV water dielectric accelerator and net current through the beam-plasma system. The unmagnetized plasma is produced by a 90-μs, 90-Å current pulse, emitted from a thermionic LaB₆ electron source, that preionizes argon fill in a 1-m-long, 15-cm-diameter Lucite tube. A microwave spectrometer detects the radio-frequency output in the 2-18, 18-26, and 26-47 GHz bands, filters, and then separates into narrower subbands. The emission takes place in two distinct phases. The 2-GHz output rises promptly with the current pulse and then decays. At 6-GHz and above, a low-level microwave prepulse appears simultaneously with the 2-6 GHz output. This output rises sharply 25 ns after the current pulse begins and includes frequencies out to and beyond 40 GHz. The radio-frequency output falls off before the current pulse ends. The microwave intensity decays monotonically with frequency     

High-Power Modulated Intense Relativistic Electron Sources with Applications to RF Generation and Controlled Thermonuclear Fusion

Recent advances in the physics and technology of the modulated intense relativistic electron beams (IREB's) are reviewed in this paper. Bunched dense electron beams can be used to construct high-power RF sources, which may critically affect future progress in fusion technology. In this paper a system is described in which electrical energy can be converted from a single pulse of relatively long duration into a series of subpulses of short duration (nanosecond and subnanosecond) and of high power (~1010 W). This electrical system consists of an IREB propagating through passive structures. The mutual interaction between the electron beam and one passive structure modifies the IREB so that power compression and beam modulation occur. When the modified IREB interacts with the next passive structure, the kinetic energy of the electrons is converted into electrical energy or RF energy. The beam current modulation depends on the injected IREB and the structure parameters. A 100-percent modulation of the current has been achieved. A single-beam source may be used for exciting radiation in a frequency range of 60 MHz to 10 GHz. In the frequency range of 60-750 MHz a modulated beam with power ~1010 W has already been achieved. IREB modulation at a frequency of ~3 GHz was performed and RF energy was extracted from the bunched beam with power output of 5 × 108 W.     

基于偏振稳定双波长保偏光纤光栅激光器的可调谐微波/毫米波产生技术

首次提出了一种基于偏振稳定双波长保偏光纤光栅激光器的可调谐微波/毫米波产生技术, 利用保偏光纤光栅选频产生两个偏振稳定的激光信号, 采用扰偏器确保激光输出的两个正交偏振态功率的一致性, 最后输入高速光电探测器产生微波/毫米波. 通过对保偏光纤光栅施加不同大小的侧向应力, 可以灵活调谐输出的毫米波频率. 实验制作了基于偏振稳定双波长保偏光纤光栅激光器的可调 谐微波/毫米波产生装置, 通过对保偏光纤光栅施加不同的轴向拉力分别产生了20.407 和22.050 GHz的微波信号. 仿真产生了60 GHz的毫米波信号, 并分析该毫米波在光纤无线通信下行链路的传输性能, 结果表明该毫米波作为副载波调制到光波上从中心站传输80 km至基站后经天线发射至用户端, 解调后仍然得到很好的眼图, 充分证明了本方案的优越传输性能.     

Performance and pulse shortening effects in a 200-kVPASOTRONTM HPM source

The PASOTRON^TM is a unique, high-power microwave source that uses a long-pulse (⩽100 μs) plasma-cathode electron-gun and plasma-filled slow-wave structure (SWS) to produce high-energy microwave pulses. The device utilizes no externally-produced magnetic fields; relying on a beam-generated plasma channel in the SWS to transport the beam. Peak powers of up to 5 MW were previously reported in C-band using a rippled-wall waveguide SWS. Scaling experiments indicated that increasing the beam voltage above the 90 kV C-band operation produces significantly higher peak powers. We report results from an L-band PASOTRON^TM BWO designed to operate at 200 kV. The plasma-cathode E-gun built for this device generated beams with voltages of up to 225 kV and currents in excess of 1 kA for pulse lengths of up to 200 μs. The L-band PASOTRON^TM BWO produced 10-20 MW of peak power in the TM₀₁ mode, which was converted in the output to a TE₁₁ mode with fixed polarization. The PASOTRON ^TM also directly produced TE-mode radiation in the 5-10 MW power range with a rotating output polarization, the rate of which can be controlled externally. The peak power and poise width was limited by the stability of the plasma channel at high peak powers and excessive plasma generation in the SWS during the long pulse length     

Generation of ultrashort microwave pulses based on cyclotronsuperradiance

We have theoretically and experimentally investigated the superradiance from a bunch of electrons rotating in a homogeneous magnetic field. A RADAN-303B modulator equipped with a subnanosecond pulse slicer has been used to generate high current subnanosecond electron bunches (250 kV, 0.1-1 kA, 0.3-0.5 ns). Transverse momentum was imparted to the electrons by a kicker. It is shown that for the experimental observation of cyclotron superradiance from high current electron bunches the optimum conditions are the conditions of group synchronism, when the translational velocity of the bunch coincides with the group velocity of the radiation propagating in the waveguide. In the 35 GHz range microwave pulses with record short duration, down to 0.4 ns, with a peak power level up to 200 kW, have been obtained     

X-band dielectric Cerenkov maser amplifier experiment

An X-band dielectric Cerenkov maser amplifier experiment is reported. The amplifier system consisted of a solid, thermionically generated electron beam propagating through a cylindrical waveguide partially filled with an annular, dielectric liner. The input signal was provided by a tunable (9-10.3 GHz) magnetron with power up to 10 kW. Electron beam voltages and currents of up to 250 kV and 100 A could be generated for 1 μs pulse durations. The system was configured to operate in the TM₀₁ mode of the dielectric-lined waveguide. In this experiment the gain of the system with respect to the length of the dielectric liner was studied at a fixed input frequency of 10.3 GHz. At electron beam parameters of 160 kV and 60 A, a power gain of 24 dB over 56 cm of interaction length was measured for an input power of 4.5 kW, corresponding to a maximum RF amplified power of 1.15 MW and 12% efficiency