High-power Čerenkov microwave oscillators utilizing High-Current nanosecond Electron beams

A short review is given of results obtained at the Institute of High-Current Electronics of the Siberian Branch of the Russian Academy of Sciences on generating high-power microwave radiation. Most of the research was devoted to a study of stimulated Čerenkov radiation from relativistic electron beams. It is shown that the efficiency of a relativistic 3-cm backward wave tube with a nonuniform coupling resistance can reach 35%. High-frequency radiation was discovered in the emission spectrum of the Čerenkov oscillators and it was shown that the nature of the radiation was associated with the stimulated scattering of low-frequency radiation by the relativistic electrons. Radiation with a power of 500 MW was obtained in the 8-mm wavelength range using a two-beam Čerenkov oscillator. High-current pulse-periodic nanosecond accelerators with a charging device utilizing a Tesla transformer were used in the experiments. The possibility was demonstrated of generating high-power microwave radiation with a pulse-repetition frequency of up to 100 Hz. An average power of ∼500 W was achieved from the relativistic oscillators. A relativistic backward wave tube with a high-current electron beam was used to make a prototype nanosecond radar device. Some of the results presented were obtained jointly with the Russian Academy of Sciences Institute of Applied Physics. Questions concerning multiwave Čerenkov interaction are not considered in this paper. Institute of High-Current Electronics, Siberian Branch of the Russian Academy of Sciences, Tomsk. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 5–20, December, 1996.     

Controlling the radiation frequency of a plasma relativistic microwave oscillator during a nanosecond pulse

It is shown experimentally and by numerical simulation that the radiation frequency of a 50-MW plasma relativistic microwave oscillator can be varied within 15% during a 60-ns-wide pulse by varying the plasma concentration. The plasma is generated by pre-ionization of a low-pressure gas. When the degree of ionization increases in a microwave field, the radiation frequency rises. Conversely, when plasma electrons are forced out by the electrostatic field of a high-current relativistic electron beam, the radiation frequency declines. By appropriately selecting the initial gas pressure and degree of gas ionization, one can control both trends and thereby the radiation frequency.     

Variation in the radiation frequency of a plasma relativistic microwave oscillator within its nanosecond pulse

The radiation spectrum of a plasma relativistic microwave oscillator with a pulse power of 50 MW operating in the 10-GHz frequency range is studied experimentally. During a 60-ns-long microwave pulse, the radiation frequency may both remain constant and change by more than 1.5 GHz. The pressure of a gas that ionizes in the microwave field has a significant effect on the radiation frequency and thereby changes the concentration of a pregenerated plasma.     

Increase in the average radiation power of a plasma relativistic microwave generator

The operation of a pulse-periodic plasma relativistic microwave generator with a pulsed power of 50 MW was experimentally studied. A change in the shapes of the electron collector and output unit allowed a significant increase in the average emission power. The microwave pulse duration was increased from 30 to 70 ns, and the repetition rate of microwave pulses was increased from 5 to 50 Hz.     

Self consistent multi-fluid FDTD simulations of a nanosecond high power microwave discharge in air

FDTD simulations of the Maxwell equations are combined with the multi-fluid plasma equations to study the dynamics of a high power microwave discharge in air. The breakdown takes place in a short time of a few nanoseconds and the concentrations of electrons, ions, excited species, and the dissociation products are quickly enhanced. The breakdown time decreases with decreasing of the pressure and the pulse amplitude, while increases with increasing of the pulse width. N${{}_2}^{+}$ and O${}_2^{+}$ are the most important positive ions, whereas O^? is the most populated negative ion. For a single microwave pulse, the electron number density is large up to 1 μs, and the dissociation and excitation continue to increase the small radicals and excited species. Then the electron number density drops and the population of excited species declines. The ozone production becomes important after 1 μs when the three body association of O and O₂ dominates over the dissociation processes. The ozone number density continues to grow up to 5 ms, and then saturates at a value of 10²² m^?3. Quenching of electronically excited nitrogen molecules by O₂ molecules and the subsequent dissociation to atomic oxygen and generation of NO, are found to be important and can play a significant role in the ultrafast gas heating.     

Bound states of two-dimensional relativistic harmonic oscillators

We give the exact normalized bound state wavefunctions and energy expressions of the Klein－Gordon and Dirac equations with equal scalar and vector harmonic oscillator potentials in the two-dimensional space.     

Coherent bremsstrahlung from relativistic channelled positrons

Poor beam collimation leads to overcompensation of suppression of coherent bremsstrahlung in the axial channelling case. This fact has been used to study the effect of beam divergence on the radiation emitted by relativistic (axially) channelled positrons. It has been found that due to beam divergence in the experiment of Alguard and co-workers in which radiation of 56 MeV positrons channelling along 〈110〉 rows of a silicon crystal is observed, coherent bremsstrahlung becomes an important contributing factor to the high frequency part of the observed spectrum.     

同轴慢波结构相对论高功率微波产生器理论分析

推导了同轴波导的空间电荷限制流,其值大于圆波导的空间电荷限制流。因此在阴极电势和束流相等的情况下,同轴波导中的束流具有更高的动能,同轴器件有可能获得更高的微波转换效率。理论推导出同轴慢波结构中考虑束流空间电荷影响的色散方程,利用Matlab进行了编程求解。不考虑束流空间电荷影响时,编程计算结果与Superfish模拟结果一致。由考虑束流空间电荷影响的色散方程数值计算结果,可知文献中提出的同轴慢波结构相对论高功率微波产生器工作在准TEM模的π模,频率为7.67 GHz,峰值时间增长率较高,电子束损失的能量与其初始能量之比为34%。这些结果均与文献中的数值模拟结果一致。同时理论分析说明该种器件无论在能量转换效率,还是在产生微波脉冲的上升时间上均具有优势。     

同轴慢波结构相对论高功率微波产生器理论分析

 推导了同轴波导的空间电荷限制流,其值大于圆波导的空间电荷限制流。因此在阴极电势和束流相等的情况下,同轴波导中的束流具有更高的动能,同轴器件有可能获得更高的微波转换效率。理论推导出同轴慢波结构中考虑束流空间电荷影响的色散方程,利用Matlab进行了编程求解。不考虑束流空间电荷影响时,编程计算结果与Superfish模拟结果一致。由考虑束流空间电荷影响的色散方程数值计算结果,可知文献中提出的同轴慢波结构相对论高功率微波产生器工作在准TEM模的π模,频率为7.67 GHz,峰值时间增长率较高,电子束损失的能量与其初始能量之比为34%。这些结果均与文献中的数值模拟结果一致。同时理论分析说明该种器件无论在能量转换效率,还是在产生微波脉冲的上升时间上均具有优势。     

Waveguide quasi-optical cavity for short-wave relativistic oscillators

A high-Q quasi-optical cavity consisting of wealky irregular axisymmetric waveguides is proposed for generation of high-power radiation in a ubitron with a high-current electron beam. The propagation of natural symmetric magnetic waves in an equivalent transmission line is studied for selection of the cavity geometry. The experimental data on electrodynamic mode selection agree with theory.Institute of High-Current Electronics, Siberian Division, Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 36, No. 2, pp. 192–200, February, 1993.     

Coherent bremsstrahlung of relativistic electrons in antiferromagnets

The coherent bremssstrahlung (CB) of relativistic electrons in antiferromagnetic crystals is studied theoretically. It is shown that the internal magnetic field of an antiferromagnet has a negligible effect on CB. The complete CB spectrum is calculated for hematite, -Fe₂O₃.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 57–61, February, 1988.     

Coherent dissociation of relativistic 12N nuclei

The dissociation of relativistic ¹²N nuclei having a momentum of 2 GeV/c per nucleon and undergoing the most peripheral interactions in a track emulsion is studied. The picture of charged topology of product ensembles of relativistic fragments and special features of their angular distributions are presented.     

Coherent dissociation of relativistic 9C nuclei

Results on the coherent dissociation of relativistic ⁹C nuclei in a nuclear track emulsion are described. These results include the charge topology and kinematical features of final states. Events of ⁹C → 3³He coherent dissociation are identified.     

Periods of relativistic oscillators with even polynomial potentials

The authors modify a non-perturbative variational approach based on the Principle of Minimal Sensitivity to calculate the periods of relativistic oscillators with even polynomial potentials. The optimization of the variational parameter is adapted by introducing additional free parameters whose values are set using the ultrarelativistic limit of the period as a boundary condition. Compact general approximations for the potentials , and prove to be accurate over the whole solution domain and even for large values of m.     

基于离轴高增益速调管的X波段高功率合成技术研究

为了克服强流高增益速调管放大器中的自激振荡和适应低阻抗脉冲功率源发展的需要,利用高阻抗X波段五腔高增益速调管放大器进行了离轴八注八管高增益速调管功率合成技术研究,在频率为9.47 GHz、模拟输出功率为284 MW、增益为51.6 d B和效率为35.5%条件下,该器件整管微波输出稳定.在三维模型中,在离轴54 mm条件下该器件的微波输出特性稳定.基于实验室现有4.5 T(长1.1 m,室温孔径为150 mm)超导磁体,进行了八注八管高增益速调管的整管模拟,每个器件实现284 MW的微波输出.最后,为实现GW级功率输出,利用HFSS软件设计了用于离轴八注八管高增益速调管功率合成的八合一功率合成器,将该合成器同八注八管高增益速调管结合,模拟得到功率为1.84 GW、增益为50.7 d B、效率为28.8%的微波输出.