合肥光源数字横向逐束团反馈系统

为了克服横向耦合束团不稳定性对合肥光源的不利影响,在合肥光源(HLS)研制了一套数字横向逐束团反馈系统。该系统使用直接采样前端,同时针对合肥光源水平方向工作点和垂直方向工作点太过接近的情况,修改了数字处理器的FPGA程序,使得单个处理器能够实现独立的双通道反馈。束流试验验证了反馈系统能有效抑制横向不稳定性,并可以提高注入流强。     

用横向反馈系统对上海光源多束团不稳定性的诊断

在上海光源二期升级改造过程中，为了解和追踪由阻抗引起的多束团不稳定性变化以及升级后的横向反馈系统对这种不稳定性的抑制效果，在机器研究中利用新反馈处理器的诊断工具记录了束流不同状态下的横向运动过程，分析得到了最主要的横向多束团不稳定模式在束流稳态、注入瞬态以及增长-衰减过程中的变化情况，评估了横向反馈的作用效果，计算出该模式增长率/阻尼率以及增长率与束流的依赖关系。     

Libera数字束流位置处理器在工作点测量中的应用

 数字信号处理技术在现代束流诊断中有成熟的应用，特别是在束流位置检测器信号分析和工作点测量时有优越的性能。在合肥光源工作点测量中,采用高斯白噪声激励起束流横向振荡，再利用Libera数字束流位置处理器采集激励后的束流位置信号，并进行幅度解调得到束流横向振荡频率，再利用Matlab进行快速傅里叶分析处理，得到工作点的小数部分，从而实现工作点测量。在合肥光源上进行实验，测量得到其水平工作点是3.535 2，垂直工作点是2.629 9。     

合肥光源逐束团横向反馈系统

 介绍了在合肥光源研制的一套横向(x, y方向)高频、宽带逐束团测量和反馈系统,以及抑制耦合束团不稳定性的初步实验。其中重点介绍了在该系统研制过程中所涉及的部分关键技术：矢量运算模块的开发使得反馈系统的调试简易方便;Notch滤波器用于滤除反馈信号中的直流分量以及回旋频率分量,节省反馈功率;激励条带的研制。初步的反馈实验结果表明：反馈系统开启后不稳定性振荡得到抑制。     

Stability of an ion beam in synchrotrons with digital filters in the feedback loop of a transverse damper

The stability of an ion beam in synchrotrons with digital filters in the feedback loop of a transverse damper is treated. A transverse feedback system (TFS) is required in synchrotrons to stabilize the high intensity ion beams against transverse instabilities and to damp the beam injection errors. The TFS damper kicker (DK) corrects the transverse momentum of a bunch in proportion to its displacement from the closed orbit at the location of the beam position monitor (BPM). The digital signal processing unit in the feedback loop between BPM and DK ensures a condition to achieve optimal damping. Damping rates of the feedback systems with digital filters are analysed in comparison with those in an ideal feedback system.     

合肥光源逐束团测量和横向束流反馈系统设计

 介绍了在合肥光源开展逐束团测量（横向和纵向）和横向束流反馈系统研究和研制的重要性,同时还介绍了设计思想。合肥光源高频频率为204 MHz，因此，系统至少需要100 MHz的带宽。还较详细地介绍了宽带部件和系统参数的选择原则。该系统不仅可用于研究由于高频腔中的高阶模和真空室的阻抗壁效应所引起的耦合束团不稳定性，而且还能抑制耦合束团不稳定性振荡、快速束流离子不稳定性和注入大幅度振荡等，从而将提高机器的运行性能。     

Chaos synchronization in semiconductor lasers with polarization-rotated optical feedback

Chaotic oscillations of the transverse magnetic (TM) mode, which is not a common lasing mode, are excited by using polarization-rotated optical feedback from the transverse electric (TE) mode in a semiconductor laser. In our previous paper, we found that the dynamics were strongly dependent on their RF components under the condition of moderate optical feedback from the TE mode to the TM mode and that they were divided into three RF regions; low-pass filtered signals with a lower frequency than the laser relaxation oscillation frequency, intermediate RF components including the relaxation oscillation frequency, and high-pass filtered signals with a higher frequency higher than the relaxation oscillation frequency. Depending on the frequency bands, the laser outputs showed different correlations. In the present study, using such schemes, the polarization-rotated beam from a transmitter laser (i.e., the rotated TE-mode beam of a transmitter laser) is injected into a receiver laser. We experimentally observe chaos synchronization in accordance with the dynamics of RF components on the transmitter laser side. We also perform numerical calculations using a model and obtain good agreement between the theoretical and experimental results.     

Reduction of electronic delay in active noise control systems--a multirate signal processing approach

Electronic delay has been a critical problem in active noise control (ANC) systems. This is true whether a feedforward structure or a feedback structure is adopted. In particular, excessive delays would create a causality problem in a feedforward ANC system of a finite-length duct. This paper suggests a multirate signal-processing approach for minimizing the electronic delay in the control loop. In this approach, digital controllers are required in decimation and interpolation of discrete-time signals. The computation efficiency is further enhanced by a polyphase method, where the phases of low-pass finite impulse response (FIR) filters must be carefully designed to avoid unnecessary delays. Frequency domain optimization procedures based on H1, H2, and Hinfinity norms, respectively, are utilized in the FIR filter design. The proposed method was implemented by using a floating-point digital signal processor. Experimental results showed that the multirate approach remains effective for suppressing a broadband (200-600 Hz) noise in a duct with a minimum upstream measurement microphone placement of 20 cm.     

BEPCII横向束流反馈系统的梳状滤波器

 BEPCII是一个多束团、大流强的装置, 由于高频腔的高次模和电阻壁阻抗等因素，不可避免地会出现束流不稳定性。BEPCII中采用束流反馈系统来抑制束流不稳定性。横向束流反馈系统主要包括前端电子学、信号处理电子学、反馈器件和放大器等几个部分。梳状滤波器是信号处理电子学的重要部件，利用两根长短不同的电缆以及一个功分器和合成器构成了一种简单有效的梳状滤波器，其梳状深度达到-41 dB，使用这种梳状滤波器的横向反馈系统成功地抑制了束流中出现的不稳定性。     

Review of collective beam instabilities in electron-positron storage rings

The review of studies of collective beam instabilities in electron-positron storage rings is presented. The processes of excitation and suppression of the longitudinal microwave instability, transverse mode coupling instability, longitudinal and transverse multi-bunch instabilities, and instabilities induced by an interaction of a beam with ions or electron clouds are discussed. Important equations for estimation of the threshold beam currents and the rise time of instabilities, as well as the references to the major original works are given. The methods for diagnostics and suppression of instabilities are considered using specific examples.     

合肥光源逐束团测量系统研制

 逐束团测量装置属于宽带和实时测量，足以分辨重复频率为204 MHz的相邻束团的信号，设计功能包括横向水平和垂直Beta振荡，纵向同步相位振荡，束团填充等信息的实时检测。对信号频谱分析，系统参数设计，前端射频检测，锁相环信号合成，高速数据采集以及基于PXI的整个系统作了详细介绍，分析了若干调试和实验结果，并讨论了合肥光源储存环目前存在的不稳定性及该测试手段在诊断中的应用。     

Emittance measurement & optimization for the photocathode RF gun with laser profile shaping

The Laser Undulator Compact X-ray source(LUCX) is a test bench for a compact high brightness X-ray generator,based on inverse Compton Scattering at KEK,which requires high intensity multi-bunch trains with low transverse emittance.A photocathode RF gun with emittance compensation solenoid is used as an electron source.Much endeavor has been made to increase the beam intensity in the multi-bunch trains.The cavity of the RF gun is tuned into an unbalanced field in order to reduce space charge effects,so that the field gradient on the cathode surface is relatively higher when the forward RF power into gun cavity is not high enough.A laser profile shaper is employed to convert the driving laser profile from Gaussian into uniform.In this research we seek to find the optimized operational conditions for the decrease of the transverse emittance.With the uniform driving laser and the unbalanced RF gun,the RMS transverse emittance of a 1 nC bunch has been improved effectively from 5.46 πmm.mrad to 3.66 πmm.mrad.     

Emittance measurement & optimization for the photocathode RF gun with laser profile shaping

The Laser Undulator Compact X-ray source(LUCX) is a test bench for a compact high brightness X-ray generator,based on inverse Compton Scattering at KEK,which requires high intensity multi-bunch trains with low transverse emittance.A photocathode RF gun with emittance compensation solenoid is used as an electron source.Much endeavor has been made to increase the beam intensity in the multi-bunch trains.The cavity of the RF gun is tuned into an unbalanced field in order to reduce space charge effects,so that ...     

合肥光源横向反馈系统的改进与试验结果

介绍了在合肥光源横向模拟反馈样机系统进行的改造和升级。主要包括前端束流位置信号处理模块的重建和与直流成分剔除单元模块。同时还进行了信号矢量合成模块的优化与改造、增加独立可调增益模块以及优化信号传输线路在内的重要改进。对改进后的反馈系统进行了抑制耦合束团不稳定性试验,相关试验数据分析结果表明,反馈系统提供的注入阻尼率提高了一个数量级。     

Passive and temporally continuous optical spectral analyzer of RF signals via wavelength coding

A novel approach realizing an optical spectrum analyzer for photonic detection of an unknown RF carrier signals is presented. The described module may be part of an electronic warfare system in which detection of a narrow band RF signal is required. Moreover, The RF signal is characterized by an unknown time varying carrier frequency embedded in wide band noise. The system uses a passive, fiber based photonic configuration. It allows the spectrum mapping of an incoming electronic RF signal modulated on an optical carrier. The spectral analyzer configuration uses a finite impulse response (FIR) filter that is realized by two different optical paths of parallel fibers which generate a spectral notch filter. Hence, a wavelength coding is realized by chromatic dispersion such that each wavelength is filtered by a different FIR filter. Therefore, the energy at a WDM demux output channels is actually proportional to the spectrum of the input RF signal. This spectral mapping is obtained without lose of temporal RF information.     

HLSⅡ干涉法测量储存环横向尺寸与发射度

为了满足合肥光源升级改造后测量小束流尺寸的需求,设计了干涉法测量束团尺寸与发射度系统。简要介绍了在可见光波段利用干涉法测量束团横向尺寸的原理,详细介绍了该系统的光路与软硬件系统和图像处理算法。为了消除CCD的本底噪声对测量的影响,建立了本底噪声图像与束流流强的查找表,最终得到了多束团模式下的在线实验结果。测量得到的水平尺寸为265μm,测量误差为5.78μm;垂直尺寸为114μm,测量误差为4.89μm。     

Amplitude and phase effects on the synchronization of delay-coupled oscillators

We consider the behavior of Stuart-Landau oscillators as generic limit-cycle oscillators when they are interacting with delay. We investigate the role of amplitude and phase instabilities in producing symmetry-breaking/restoring transitions. Using analytical and numerical methods we compare the dynamics of one oscillator with delayed feedback, two oscillators mutually coupled with delay, and two delay-coupled elements with self-feedback. Taking only the phase dynamics into account, no chaotic dynamics is observed, and the stability of the identical synchronization solution is the same in each of the three studied networks of delay-coupled elements. When allowing for a variable oscillation amplitude, the delay can induce amplitude instabilities. We provide analytical proof that, in case of two mutually coupled elements, the onset of an amplitude instability always results in antiphase oscillations, leading to a leader-laggard behavior in the chaotic regime. Adding self-feedback with the same strength and delay as the coupling stabilizes the system in the transverse direction and, thus, promotes the onset of identically synchronized behavior.     

基于FPGA与Matlab的数字正交解调器的设计

为有效提取测控系统输入信号的幅度和相位信息,设计了基于FPGA与Matlab的信号数参考文献6文献类型、文献出处、年份字正交解调器。在Matlab/Simulink环境中产生一路调幅信号,并在此环境下利用5个直接I型的4阶FIR滤波器节搭建了20阶FIR滤波器;利用FPGA查表法实现数控振荡器(NCO),并控制1路调幅信号与正交的正、余弦信号分别进行数字混频处理;对经FPGA数字混频处理后的两路倍频分量和基频分量信号进行滤波处理,经处理后的信号在FPGA的控制下进行相加处理。最后在硬件平台上进行了仿真测试实验,验证了该方案的正确性和可行性。     

合肥光源横向束流反馈系统中矢量运算单元和光纤陷波滤波器的研制

 合肥光源横向束流反馈系统已经建成,着重介绍了系统中矢量运算单元和光纤陷波滤波器的研制。矢量运算单元中使用混频器控制信号的衰减,调节控制电压的大小以控制反馈信号的相位;光纤陷波滤波器创新性地提出用光纤延时制作陷波滤波器,很好地滤除了信号中的回旋频率分量,节省了反馈功率。     

Beam dynamics in synchrotrons with digital wideband transverse feedback systems

Current researches on beam dynamics in synchrotrons with digital wideband transverse feedback systems are reviewed. Particular attention is given to quantitative and qualitative regularities in frequency shifts and decrements of coherent betatron oscillation damping when feedback loop signals are digitally processed. Theoretical predictions are compared with the experimental data obtained at the Large Hadron Collider.