行波管放大器的非线性混沌特性

以一组非线性方程为基础,从混沌动力学角度,通过计算电子的相空间轨道和辐射场的时空分布图谱,简要分析了行波管放大器的时空混沌特性,计算了行波管输出功率的演化。计算结果表明:行波管放大器辐射场与电子束是一个非线性相互作用的耗散系统,其参数影响整个系统的行为演化,当电流和失谐量等参数变化并超过一定阈值时,系统出现时空混沌特性,输出具有连续的宽频谱性。     

Nonlinear dynamics in wurtzite InN diodes under terahertz radiation

We carry out a theoretical study of nonlinear dynamics in terahertz-driven n⁺nn⁺ wurtzite InN diodes by using time-dependent drift diffusion equations. A cooperative nonlinear oscillatory mode appears due to the negative differential mobility effect, which is the unique feature of wurtzite InN aroused by its strong nonparabolicity of the Γ₁ valley. The appearance of different nonlinear oscillatory modes, including periodic and chaotic states, is attributed to the competition between the self-sustained oscillation and the external driving oscillation. The transitions between the periodic and chaotic states are carefully investigated using chaos-detecting methods, such as the bifurcation diagram, the Fourier spectrum and the first return map. The resulting bifurcation diagram displays an interesting and complex transition picture with the driving amplitude as the control parameter.     

行波管放大器中的电子混沌现象

用自洽方程模拟了波-粒相互作用过程中的电子混沌行为.结果表明：随着电流的增大，电子在相空间的运动轨道将变得混沌，混沌轨道受失谐量的影响.在时间上，电子混沌比场的极限环和混沌振荡出现要早.与场出现极限环振荡的电流阈值相比,出现电子混沌的电流阈值要小；在场呈极限环状态的“软”非线性区域，电子的混沌轨道占据大部分相空间；而在场混沌的“硬”非线性区域，混沌轨道则弥漫在整个相空间.当电流一定时,电子的混沌运动图样是不变的；在一定的电流范围内， 场的极限环和混沌振荡特征是确定的， 但它们的输出功率是不确定的. 关键词： 行波管放大器 电子混沌 相空间轨道 非线性相互作用     

基于继电特性函数的互联电力系统混沌控制

电力系统中的混沌振荡对整个互联电网具有极大危害.本文利用Lyapunov指数、分岔图、相平面图和功率谱等分析一个简单互联电力系统的动力学行为,研究电力系统对电磁功率扰动幅值的敏感性.同时,提出一种基于继电特性函数的准滑动模态控制方法,对系统进行混沌振荡抑制,使系统快速平滑地到达控制目标.实验表明,该方法不仅能够缩短控制时间,减少因参数过大带来的系统冲击,而且对高频抖动也有很好的抑制作用,具有较强的鲁棒性.     

Nonlinear dynamics in wurtzite InN diodes under terahertz radiation

We carry out a theoretical study of nonlinear dynamics in terahertz-driven n+ nn+ wurtzite InN diodes by using time-dependent drift diffusion equations.A cooperative nonlinear oscillatory mode appears due to the negative differential mobility effect,which is the unique feature of wurtzite InN aroused by its strong nonparabolicity of the Γ 1 valley.The appearance of different nonlinear oscillatory modes,including periodic and chaotic states,is attributed to the competition between the self-sustained oscillation and the external driving oscillation.The transitions between the periodic and chaotic states are carefully investigated using chaos-detecting methods,such as the bifurcation diagram,the Fourier spectrum and the first return map.The resulting bifurcation diagram displays an interesting and complex transition picture with the driving amplitude as the control parameter.     

Sources of intensive noise signals of millimeter wave band

The new method of the CW intensive noise signals excitation in millimeter wave band has been studied. With this aim in mind the O-type Backward Wave Oscillators, operating in chaotic oscillation regime, are proposed to use. The noise sources, based onBWO, have a high efficiency, universal power spectrums and feasibility of electronic tuning of the noise signal frequency in the relative range of 4–10%. Low voltage noise sources, operating in the bands needed over the range from 30to 60GHz, make possible output power of 8 – 25W and 4W respectively and 3 –dB power spectrum width more than 300M H z. Application of the suitableBWO offers to excite the noise signals in decimeter and centimeter ranges too.     

Experimental study of complex dynamics in a delayed-feedback multiple-cavity klystron self-oscillator

The main characteristics of a delayed-feedback multiple-cavity klystron oscillator with various oscillation modes (single-frequency oscillations, as well as regular and chaotic self-modulations) are studied experimentally. Maps of dynamic modes on the beam current-accelerating voltage plane are presented. Basic scenarios of transition to chaos are considered. As the beam current and amount of feedback increase, regular and chaotic oscillation modes are found to alternate in a complex manner. It is shown that one can significantly increase the power of chaotic oscillations by appropriately tuning the control parameters.     

直接调制光反馈半导体激光器产生超宽带信号

利用直接电流调制光反馈半导体激光器产生了符合美国联邦通信委员会关于室内无线通信频谱限定的超宽带(UWB)微波信号.基于光反馈半导体激光器速率方程组, 数值分析了偏置电流、反馈强度对混沌UWB脉冲信号的影响.研究表明, 混沌UWB脉冲频谱的-10 dB带宽分别随着偏置电流的增大和反馈强度的增强而逐渐增加; 中心频率分别随着偏置电流的增大和反馈强度的增强而逐渐增大.实验中, 产生了中心频率为6.6 GHz, -10 dB带宽为9.6 GHz的混沌UWB信号. 进一步, 通过调节偏置电流和反馈强度, 可实现混沌UWB信号的中心频率和-10 dB带宽的可调谐输出, 实验结果和数值分析相符合.此外, 实验产生的混沌UWB信号经过34.08 km的光纤传输后, 其频谱形状几乎没有发生变化, 表明该方法所产生的混沌UWB信号对光纤色散有较大的容忍度. 关键词： 超宽带 混沌激光 光反馈 直接调制     

Wideband chaotic oscillation in a self-oscillatory system with a nonlinear transmission line on magnetostatic waves

Wideband chaotic microwave oscillation in a ring self-oscillatory system is studied. The system includes a solid-state power amplifier and a wideband nonlinear transmission line with a ferromagnetic film in which magnetostatic waves of different types are excited. It is found that the eigenmodes of the self-oscillatory system excited in the passband of the transmission line on magnetostatic waves become noisy because of spin wave parametric excitation due to the magnetostatic wave and nonlinearity of the power amplifier. A continuous spectrum of modes observed in the wideband chaotic signal is associated with the presence of a descending portion in the dynamic characteristic of the nonlinear transmission line, which arises when a magnetostatic surface wave is excited.     

微波管中离子张弛振荡的混沌现象

微波管中离子张弛振荡引起的噪声对其工作性能有很大影响，已成为微波管领域研究的焦点之一.用包络方程描述电子束特性，用离散的宏粒子模型描述离子特性，在此基础上编写了一维粒子模拟程序，对行波管与速调管模拟，得到张弛振荡的时间序列；将振荡看作是一个复杂非线性动力学系统的响应，分析了离子张弛振荡时间序列的功率谱、重构相图及Lyapunov指数，指出离子张弛振荡具有混沌性质，为研究离子张弛振荡的控制与带有离子振荡噪声信号的处理提供了参考. 关键词： 张弛振荡 粒子模拟 微波管 混沌     

电力系统混沌振荡的等效快速终端模糊滑模控制

电力系统混沌振荡被认为是大型互联电力系统停电事故的主要原因, 本文通过相图、 李雅普诺夫指数图和时域波形图分析了二阶电力系统混沌振荡的动力学行为, 并提出了等效快速终端模糊滑模控制来抑制电力系统混沌振荡, 使其恢复到同步运行状态. 仿真结果表明, 所提出的控制方案不仅具有较快的收敛速度, 而且能够柔化控制信号, 减少控制能量, 并且能有效地降低抖振. 关键词： 电力系统混沌振荡 等效滑模控制 模糊滑模控制 快速终端滑模控制     

Stochastic and chaotic relaxation oscillations

For relaxation oscillators stochastic and chaotic dynamics are investigated. The effect of random perturbations upon the period is computed. For an extended system with additional state variables chaotic behavior can be expected. As an example, the Van der Pol oscillator is changed into a third-order system admitting period doubling and chaos in a certain parameter range. The distinction between chaotic oscillation and oscillation with noise is explored. Return maps, power spectra, and Lyapunov exponents are analyzed for that purpose.     

A Fast Computation of the Start-Oscillation Current of Backward Wave in MMW HTWT's

Backward wave oscillation can be troublesome in high power helix TWT, especially millimeter wave helix traveling wave tubes (MMW HTWT's). To suppress these oscillations, start-oscillation current of backward wave has to know when MMW HTWT's are designed.A fast computation of the start-oscillation current for MMW HTWT's is presented. It is shown that the computed values are agreed with the experimental results in Ka band.     

螺距和磁场强度与周期的跳变在Ka波段行波管中的应用

以弱色散特性的扇形金属-介质夹持杆螺旋线慢波结构的Ka波段行波管作为研究对象,进行了互作用特性仿真研究。采用螺距跳变和磁场跳变技术进一步提高了该行波管在工作频带的输出功率和电子效率,并解决了电子注散焦问题。设计结果表明:当工作电压为9 kV、工作电流为210 mA时,行波管在24~40 GHz整个频带内,各频点的增益在37.7~48.7 dB之间,电子效率在15.18%~19.42%之间,输出功率大于286 W。此结果较之均匀周期的设计结果,电子效率增幅在4.19%以上,输出功率增长率在4.3%以上,尤其在26~37 GHz范围内,电子效率增幅达到了11.8%以上,输出功率增长率达11.9%。     

Homoclinic connections and period doublings of a ship advancing in quartering waves

The large-amplitude motions of a ship running in waves are analyzed with a mathematical model reduced to a system of eight coupled nonlinear ordinary differential equations. Bifurcation analysis in relation to the surf-riding condition, with control parameter the angle of the rudder, shows the existence of a region of oscillatory behavior, containing also a chaotic domain. This region ends with a homoclinic connection and a dangerous jump toward the overtaking-wave mode, which can incur ship capsize. Addition of linear control removes the chaotic domain while giving rise to new regions of oscillation. (c) 1996 American Institute of Physics.     

Generation and synchronization of feedback-induced chaos in semiconductor ring lasers by injection-locking

A smart scheme for chaotic signal generation in a semiconductor ring laser (SRL) with optical feedback is proposed and investigated numerically. The chaotic oscillation in the SRL can be generated by the partial reflection of the laser output. Time series, attracter and the power spectrum, as well as the Lyapunov exponent spectrum, are calculated and analyzed. We also study the synchronization scheme of feedback-induced chaos in SRLs by optical injection that consists of a drive SRL with optical feedback and a response SRL with optical injection from the drive laser. High-quality synchronization is achieved with suitable injection strength and detuning frequency between the drive and the response SRLs.     

Transverse instability of line defects of period-2 spiral waves

Spiral waves that arise in period-2 oscillatory media extended in space generically bear "line defects" along which the local kinetics exhibits a period-1 oscillation. Locally, these defect structures can be viewed as a front separating two period-2 oscillatory domains oscillating 2pi out of phase. Here we show that their shape can become sinusoidal with a transverse instability as in bistable fronts. This instability eventually leads to a line-defect filled spatiotemporal chaotic state having erratic proliferations, annihilations, and regenerations of line defects. The same sequence of phenomena is observed in a model reaction-diffusion system as well as in an experimental system.     

Transition from periodic to non-periodic oscillation observed in a mathematical model of bioconvection by motile micro-organisms

Bioconvection observed in a culture of motile micro-organisms was analyzed numerically. The governing equations are the Navier-Stokes equations with the Boussinesq approximation and a diffusion equation for the motile micro-organism. A transition from a static condition to periodic oscillation was observed according to the increase of the Rayleigh number. It was found that the system of bioconvection could be led into chaotic conditions via a single-frequency oscillatory behavior to a sequence of period-doubling bifurcations by increasing the Rayleigh number, which is analogous to Bénard convection.     

Relaxation Oscillation Enhancement and Coherence Collapse in Semiconductor Lasers with Optical Feedback

The dynamic characteristics of a semiconductor laser with optical feedback are strongly dependent on the injection current and the reflectivity and position of the external feedback reflector. We investigated the relaxation oscillation enhancement and coherence collapse state of the laser oscillation based on the laser rate equations. It is well known that laser output power jumps with increase of the injection current due to external mode transition. But here for the first we time demonstrate the existence of a chaotic scenario within successive laser power jumps. The results calculated by numerical simulations based on the rate equations are compared with those of the experiments and good coincidence between them is found.     

Simulations of a two-stream backward-wave oscillator with a slot-hole structure

We study a two-stream backward-wave oscillator with a slot-hole structure at short millimeter waves with the help of a three-dimensional particle-in-cell simulation. In order to increase the interaction region of the electron beam, the efficiency and the output power, a slot-hole loaded rectangular waveguide structure used as the high-frequency system is proposed. Based on the mechanism of the backward-wave oscillator, a slow-wave oscillator with a frequency of 0.14 THz is designed. The simulations show that the output power and the efficiency of the oscillator can be enhanced due to the coupling between the two beams through the slot holes. The interaction efficiency is 5.18%, and the starting current density is below 5 A·cm^-2 for the two beams. These attractive results indicate that, based on the two-stream backward-wave oscillator, we can get short millimeter wave sources with high power and low current density.