Nonlinear Investigation of a Coaxial-Waveguide Cyclotron Autoresonance Maser Amplifier

A nonlinear approach is presented to simulate the coaxial-waveguide cyclotron autoresonance maser (CARM) amplifier. Simulation shows an interesting result that the efficiency of a coaxial-waveguide CARM amplifier may be increased from 7.5% to 33.9% by tapering the magnetic field.     

外开槽同轴波导大轨道回旋自谐振脉塞放大器

 运用大轨道电子束,对外开槽同轴波导回旋自谐振放大器进行了线性动力学理论分析和非线性自洽模型模拟。由线性动力学理论分析和非线性模拟得到的结果在线性增长部分吻合得很好。为了有效抑制绝对不稳定性,对电子束流的选择进行了讨论。计算结果表明：对于电压为700 kV, 电流为100 A, 电子束纵横向速度比为0.8的大轨道电子束, TE₅₁外开槽同轴波导回旋自谐振脉塞放大器的峰值功率和峰值效率分别可以达到6.27 MW和8.96%。     

THz回旋自谐振脉塞多模束波互作用非线性模拟

为了有效分析模式竞争,建立了回旋自谐振脉塞（CARM）多模束波互作用自洽非线性理论模型,并具体模拟研究了工作模式为TM51、频率为0.35 THz的高阶横磁模CARM中大轨道相对论电子束与多电磁模式的互作用过程。模拟结果表明:与回旋管不同,THz频段CARM可以有效工作于高阶TM模式,且具有较高的输出功率和增益;通过对工作参数的优化,可使工作模式的功率增长具有绝对优势,而竞争模式得到有效抑制;高阶TM模式THz频段CARM的性能对工作参数的变化十分敏感,在参数设计过程中必须对其进行多模束波互作用模拟分析。     

Self-consistent simulation of cyclotron autoresonance maseramplifiers

A self-consistent, one-dimensional model of the cyclotron autoresonance maser (CARM) amplifier is developed, and numerical simulations based on this model are described. Detailed study results of the CARM gain and efficiency for a wide range of initial energy and velocity spreads are presented. The interaction efficiency is found to be substantially increased when the axial magnetic field is tapered. Efficiencies of greater than 41% are obtained for a 140-GHz CARM amplifier with a tapered axial magnetic field and a 700-kV 4.5-A electron beam with parallel velocity spreads of less than 1%. A discussion of the nonlinear bandwidth and interaction sensitivity to axial-field inhomogeneities is presented     

Self-consistent theory of cyclotron autoresonance maser in a uniform planar waveguide

A general dispersion relation for the cyclotron autoresonance maser (CARM) that takes into account self-consistent couplings between TE, TM and ac space charge perturbations in a uniform planar waveguide is derived. The dispersion relation predicts enhanced growth rate due to ac space charge effects. Results from computer simulations of a planar CARM amplifier are presented to support this finding.     

Gain and bandwidth of the gyro-TWT and CARM amplifiers

Issues concerning the interpretation of gain and bandwidth from the dispersion relation are examined for the gyrotron traveling wave tube (gyro-TWT) and the cyclotron auto-resonance maser (CARM) amplifiers. A general method for the determination of the critical current for oscillation is illustrated. Despite the broad bandwidth predicted for the CARM amplifier by the commonly employed dispersion relation, it is seen in particle simulation that single-particle interaction. Rather than collective amplification, prevails over much of the band. Reasons for the discrepancy are analyzed     

Mode Competition in the Gyro-Peniotron Oscillator

The gyro-peniotron oscillator holds great promise for generating microwave radiation with efficiencies far greater than those obtainable through the electron cyclotron-maser interaction. Theoretical modeling has shown that extremely high efficiencies (>90 percent) may be possible for the gyro-peniotron. Stable operation of the gyro-peniotron oscillator requires, however, that mode competition from the electron cyclotron-maser interaction be avoided. This mode competition can be quite serious since the cyclotron-maser start-oscillation currents are generally much smaller than those from the peniotron interaction. We examine here the start-oscillation conditions for the peniotron and the electron cyclotron-maser interactions from linear theory. Both large-orbit axis-encircling and small-orbit off-axis electron beams are investigated. Conditions under which a gyro-peniotron oscillator may be operable are presented, including the important limitations on the spread of the beam guiding center. The results of this study indicate that mode competition for the gyro-peniotron can be easily avoided for TE211 and other low-order azimuthal modes when a large-orbit axis-encircling beam is used. Serious mode competition and gyro-peniotron suppression is found for small-orbit off-axis beams.     

Kinetic theory of a novel carm oscillator with axisymmetrical quasi—Optical cavity of oblique rotation at arbitrary angle

A novel CARM oscillator with axisymmetrical quasi—optical cavity of oblique rotation at arbitrary angle (AQCORAA) is studied using the kinetic theory. By means of the method of local field expansion in the coordinates of the guiding centre and the Laplace transform, the beam—wave interaction power, starting current density and frequency shift are derived. The formulas presented here may have some potential applications for more further studies of the CARM oscillator with AQCORAA.This work is supported by National Science Fund of China, and by Doctoral Fund of Education Committee of China.     

Kα波段TE01模基波回旋速调放大器的设计与实验

在回旋速调放大器自洽非线性大信号理论分析和数值计算的基础上,给出了一支Kα波段TE₀₁模4腔基波回旋速调放大器的设计方案,并完成了样管的研制.同时对样管进行了热测实验,得到了如下实验结果:注电压为70 kV,电流为10 A,输入功率为60 W,磁场强度1.31 T,中心频率34 GHz,峰值功率245 kW,平均功率大于3 kW,增益36.1 dB,效率 35%,3 dB带宽大于280 MHz. 关键词： 回旋速调放大器 注-波互作用 群聚腔 输入腔     

Theory, Design, and Operation of Large-Orbit High-Harmonic Gyroklystron Amplifiers

The high-harmonic gyroklystron is a compact RF amplifier which relies on the synchronous interaction between large-orbit axis-encircling electrons and high-order azimuthal cylindrical cavity TEn11 modes. Because of this unique structure, it offers the promise of moderate- to high-millimeter-wave output power. Experimental results for a fifth-harmonic two-cavity device are compared to both small-signal analytic theory and large-signal numerical calculations which assess gain, bandwidth, sensitivity to longitudinal velocity spread, self-oscillation, and saturation characteristics. Principal theoretical results include the transition to infinite gain as the start-oscillation current threshold is reached as well as the demonstration of the insensitivity of the small-signal gain to parallel velocity spread. The required high-energy rotating electron beam is provided through gyroresonant RF acceleration. To date, over 20 dB of small-signal gain has been achieved at 11.3 GHz in a 1.3-kG magnetic field. The design of a four-cavity configuration is also presented along with simulation of its gain, bandwidth, amplitude modulation (AM) and phase modulation (PM) sensitivity, dependence upon guiding-center spread, and large-signal saturation characteristics. This device has been constructed and initial tests have yielded a gain of 30 dB. Gain in excess of 50 dB is predicted.     

一种新型缓变倒向场大回旋电子枪

提出了一种新的利用缓变倒向场获得大回旋电子注的设计方法,在分析缓变倒向场中电子的运动规律和引起偏心与速度零散的各种原因的基础上,设计了一支大回旋电子枪.与传统设计思路不同,这种大回旋电子枪既不追求形成薄的管状电子束,又不追求突变的倒向磁场,因而极大降低了制管工艺和结构复杂性;阴极发射带可以位于倒向点前的轴向磁场幅值渐减区域,通过控制各条轨迹起始点的正则角动量差异,并利用多种不利因素的相互抵消作用来减小偏心与速度零散.模拟计算结果与理论分析一致,表明通过微调电磁场使各种不利因素相互抵消可以显著提高大回旋电子 关键词： 缓变倒向场 大回旋电子枪 偏心 速度零散     

A passive network model for large diameter thermoacoustic tube systems and its experimental verification

Linear thermoacoustic theory is currently well accepted for simulating thermoacoustic systems, and correction is used to reduce the discrepancy between calculations and experimental results for turbulent flow. In order to calculate passive tube systems and make linear thermoacoustic theory coincide closely with experiments, a passive network model based on fluid network theory is derived. An amendment method is proposed to further correct for turbulence by amending thermal and viscous penetration depths when the ratio of the tube radius to the viscous penetration depth R/δ_v is large. The experiments have been done to verify the model in the acoustic amplifier, Helmholtz resonator, and inertance tube. In addition, the mechanisms of such tubes are further analyzed based on the model.     

The perturbation theory multi-cavity large-orbit gyro-klystron

The paper presents an application of perturbation theory to multi-cavity large-orbit gyro-klystron. By using this theory in every cavity, a recurrence formula about the azimuthal velocity of electron is obtained, which considers the prebunching function of every cavity. Furthermore, some analytical expressions are derived, such as the bunching formula of electrons, beam-wave interaction power and the gain, etc.     

Large-orbit Subterahertz and Terahertz gyrotrons

We review briefly the main ideas and achievements in the field of physics related to shortwavelength large-orbit gyrotrons, in which the coupling of electrons with the working mode and the discrimination of parasitic modes in the case of resonance at the high cyclotron harmonic are more efficient compared with conventional gyrotrons. The results of studying a new large-orbit gyrotron with moderate electron energies of 50–80 keV and comparatively low magnetic fields of 10.5–14 T are presented. In this gyrotron, high-power single-mode generation was obtained at the second and third cyclotron harmonics in the frequency range 0.55–1.00 THz. The prospects of development and application of short-wavelength large-orbit gyrotrons are discussed.     

Electron-optical system for a large-orbit gyrotron

An electron-optical system generating a rectilinear or helical 250 keV/4 A/10 μs electron beam with a high compression factor is developed. For the former beam, a compression factor as high as 4400 and a current density of 25 kA/cm₂ are achieved. In the process of forming the helical beam, the electrons rotating about the system’s axis (paraxial beam) acquire an initial velocity in a transverse magnetic field produced by a kicker. Their pitch factor is increased to a desired (operating) value in an adiabatically growing magnetic field. In tentative experiments with the helical beam in a large-orbit gyrotron, generation was obtained at the second cyclotron harmonic (223 GHz).     

High-power harmonic gyro-TWT's. I. Linear theory and oscillationstudy

A linear theory using Laplace transforms which is applicable to both gyrotron traveling wave amplifiers (gyro-TWTs) and gyrotron backward-wave oscillators (gyro-BWOs) is presented. The validity of the linear theory is verified by comparing it with an existing nonlinear self-consistent theory based on a different approach. In conjunction with a time-dependent multimode particle simulation code, the linear theory is applied to study the stability of harmonic gyro-TWTs. It is shown that a harmonic gyro-TWT can be made stable to all forms of spontaneous oscillations by employing a multistage interaction structure and that it can generate power levels far in excess of those possible for a fundamental gyro-TWT. The linear bandwidth of a second-harmonic gyro-TWT amplifier is also calculated     

Performance Improvement of Two-way Quantum Key Distribution by Using a Heralded Noiseless Amplifier

We show the successful use of a heralded noiseless linear amplifier on the detection stage in the two-way continuous-variable quantum key distribution to improve the performance. Due to the excess noise, the secret-key rate of the two-way protocol becomes negative for a certain distance of transmission. The use of a heralded noiseless linear amplifier increases this distance by the equivalent of 20 log₁₀g dB of losses, and it also helps the two-way protocol tolerate more excess noise.     

Long Optical Delay Lines Enhanced by Ring Configuration in Optical Fibres

A long optically controlled delay line enhanced by ring configuration is demonstrated by using the group-velocity control of signal pulses based on stimulated Brillouin scattering. In experiment, two optical fibre ring cavities are used： one is used as the Brillouin laser, providing single-mode Stokes wave as probe wave; the other is used as the Brillouin amplifier, working as slow light medium. We achieve a maximum time delay of 215ns using the ring Brillouin amplifier, five times larger than the input probe pulse width of 40ns. In the meantime, a considerable pulse broadening is observed, which agrees well with the theoretical prediction based on linear theory.