Mechanism of radiation pulse shortening in plasma relativistic microwave generator

The causes of emission quenching in the plasma relativistic microwave generator are studied by numerical calculations using the particle-in-cell method. The process mechanism in which the plasma boundary moves from the coaxial collector edge with a velocity above 10⁷ cm/s is found. An electron flux with an energy of ～10⁵ eV and a current of ～10³ A is generated from the collector in the formed gap, which heats plasma and increases its potential. Microwave generation stops due to a multiple decrease in the wave reflectance from the collector. The use of the hollow collector is presumably a method for preventing microwave generation quenching.     

Scenario for output pulse shortening in microwave generators drivenby relativistic electron beams

At the present time, microwave generators driven by high current relativistic electron beams are not baked and sealed, so their inner surfaces are densely covered with molecules of gas and oil. This allows the production of microwave pulses of 10^-8 s to 10^-7 s duration, but not longer. A microwave pulse termination scenario is speculated as follows: (1) Electrons oscillating in the strong RF field near the metallic surfaces multiply owing to the secondary emission (the multipactor effect); (2) the multipactor electron bombardment stimulates desorption of gas molecules from the metallic surfaces; (3) the gas undergoes avalanche RF breakdown; and (4) the resultant plasma stops microwave generation and, since electron-ion recombination is slow, does not allow the RF field to revive. At the gigawatt power level, the characteristic time of such a scenario is much shorter than that of the cathode and collector plasma expansion and electron beam instabilities. The energy output parameters of relativistic electron microwave generators can be (and usually are) improved at high pulse repetition rates. A more radical improvement is possible using the technology typical for high vacuum tubes, i.e., baking and sealing     

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.     

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.     

A theorem in relativistic electronics

This paper presents a theorem that connects the dispersion relation of the Electron Cyclotron Maser' and the oscillation equation of the Gyromonotron. This theorem gives us a simple way of obtaining the osscillating characteristics of the Gyromonotron provided that dispersion relation of the ECRM is given. Though the theorem is proved only with the case of ECRM and Gyromonotron, it holds for other kinds of Electron Masers, FEL⁴etc. and corresponding osscillators.     

Shortening of the radiation pulse from a plasma relativistic microwave generator in numerical calculations with plasma simulation by the particle-in-cell method

Spontaneous shortening of radiation pulses of Cherenkov microwave generators based on the interaction of a high-current relativistic electron beam with preliminarily generated plasma was studied in a numerical model. Microwave pulse shortening is caused by the appearance of a gradually expanding region near the collector, from which plasma is expelled by an electrostatic field of relativistic electrons. The absence of plasma results in a severalfold decrease in the plasma wave reflectance from the collector and violation of generator self-excitation conditions. The microwave emission duration increases with the plasma ion mass.     

Developing a high-current relativistic millimeter-wave gyrotron

A relativistic gyrotron fed by a 500 keV, 2 kA helical electron flow in the TE and TM modes is simulated on the basis of a self-consistent system of time-dependent equations with a non-fixed field structure and using a three-dimensional version of the KARAT PIC code. The possibility of reaching an output power 200–250 MW at a wavelength of 10 mm is shown.     

线性偏振激光在相对论等离子体中的调制不稳定性

从相对论等离体中电磁波的非线性色散方程出发,利用Karpman方法获得了线性偏振波模所满足的非线性控制方程,在非线性色散方程和非线性控制方程的基础上对线性偏振激光在相对论等离体中传播的调制不稳定性进行分析,给出了调制不稳定的时间增长率与扰动态波数之间的函数关系。     

高功率微波器件中脉冲缩短现象的粒子模拟

脉冲缩短是高功率微波器件的一个普遍现象，它阻碍了输出微波能量的进一步提高，是高功率微波研究领域中急待解决的问题.以相对论返波管作为研究对象，运用粒子模拟的方法，研究了器件表面的爆炸发射、电子束电压和电流的脉动对输出微波性能的影响，从中得到了一些有益的结论，指出由强电场引起的慢波系统表面的爆炸发射是产生脉冲缩短的重要因素 ，电子束电流和束电压的脉动也会引起脉冲缩短，并提出了相应的克服方法. 关键词： 高功率微波器件 相对论返波管 脉冲缩短 粒子模拟     

Elimination of emission quenching of plasma relativistic microwave generator

The mechanism of the development of the effect of microwave pulse shortening in a plasma relativistic microwave generator with a power of 10⁸ W is determined using numerical simulation. Methods for eliminating the causes of microwave generation quenching are proposed. It is shown that the emission time can be significantly increased.     

S波段长脉冲相对论速调管放大器中杂模振荡导致的脉冲缩短抑制研究

研究了相对论速调管放大器中的脉冲缩短问题.分析表明杂模振荡是引起脉冲缩短的重要原因.利用粒子模拟对振荡的模式进行了分析,研究了振荡的机理,在粒子模拟中利用吸收介质对杂模实现了有效的抑制.最后,在实验中解决了相对论速调管放大器中的脉冲缩短问题,在输出微波峰值功率约为920 MW时将脉宽由77 ns提高到137 ns.     

Microwave pulse phase encoding using a photonic microwave delay-line filter

A novel technique to perform microwave pulse phase encoding using an incoherent photonic microwave delay-line filter is proposed and experimentally demonstrated. Being different from a regular microwave delay-line filter, in which the time-delay differences are identical between any adjacent taps, the proposed filter has nonidentical time-delay differences. A phase-encoded microwave pulse with the required code pattern is generated by properly adjusting the time-delay differences. The chip number of a generated phase code is determined by the number of the filter taps, and the phase shift of each chip is determined by the corresponding time-delay difference. The proposed technique is verified by experiments. The generation of binary and quaternary phase-coded pulses is experimentally demonstrated.     

On self-focusing of an ultrashort intense relativistic laser pulse in a plasma

The development of the spatiotemporal (filamentation) instability of a laser pulse upon excitation of a plasma wave is studied numerically and analytically. It is shown that first, as in a medium with inertialless cubic nonlinearity, the filamentation of radiation occurs and then filaments are attracted to each other. The following evolution differs weakly from the evolution of a smoothed wave beam in a medium with inertial nonlinear response.     

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.     

Nonlinear stage of development of resistive hose instability of a high-current relativistic electron beam in a plasma

The nonlinear stage in the development of a resistive hose instability of a highcurrent relativistic electron beam in a finite-conductivity plasma has been studied in the rigid-beam model. The attenuation of the force of the interaction of the beam with the magnetic field of the total current for large beam displacements is shown to result in the stabilization of the instability. The stabilization time and the amplitudes of the oscillations in the saturation regime are determined as functions of the parameters of the beam in the plasma.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fiz., No. 10, pp. 78–81, October, 1987.