BEPC中电子云导致的束团横向尺寸增长研究

多束团正电子储存环中可能发生电子云不稳定性. 由于电子云导致的束团横向尺寸增长已经成为提高对撞机对撞亮度的主要限制因素之一. 介绍了在BEPC储存环中, 利用条纹相机直接测量由于电子云导致的束团横向尺寸增长结果, 并与模拟计算进行了比较.     

用于HLS单束团运行模式的高频剔除系统

 介绍了主要用于实现合肥光源单束团运行模式的高频剔除（RFKO）系统。该系统完全基于仪器设备(分频器、波形发生器、宽带放大器和具有I/Q调制功能的矢量信号发生器)，无任何专门设计的电子线路。高频剔除的原理是激励粒子横向振荡而丢失。激励信号产生的过程是：将取自储存环高频系统的信号进行分频，得到束团同步信号；用束团同步信号触发波形发生器，生成窄脉冲；该窄脉冲调制信号发生器，输出高频剔除信号，放大后加在条带电极上，进行束团剔除。目前获得了18 mA的单束团最高流强。改变分频数和脉冲长度，可得到其它一些周期性填充模式，其中3串6束团以及非均匀填充模式得到了实验验证。     

BEPCⅡ横向束流反馈系统样机在BEPC上的实验

为了抑制BEPCⅡ产生的耦合束团不稳定性, 提高储存环中的流强, 研制了一套逐束团横向束流反馈系统的样机并在BEPC上做了实验, 得到了理想的结果. 当束团不稳定时, 频谱仪上可以观察到横向边带, 此时将反馈系统闭环工作于阻尼状态时, 横向边带立即消失. 本文介绍了样机系统的组成、各部分的功能和实验结果.     

BEPCⅡ中电子云不稳定性模拟研究

正电子储存环在多束团运行时有可能发生电子云不稳定性(ECI)?.本文针对北京正负电子对撞机二期工程(BEPCⅡ)的具体条件,编写发展了模拟计算程序,以不同电子云密度抑制措施下的计算结果为基础,研究了耦合束团不稳定性和单束团不稳定性,给出了电子云不稳定性增长率和阈值密度以及色品对束团尺寸增长的抑制作用,为储存环中电子云不稳定性的前沿科学研究和BEPCⅡ工程设计提供了有意义的结果.     

空间电荷主导电子束的纵向聚焦设计

在空间电荷主导电子束研究中,纵向聚焦非常重要,在输运过程中由于强空间电荷力的影响,束团将很快变长并崩溃,马里兰大学的电子环设计用于方形束团和抛物线形束团的研究,环中需要用三个感应腔对束团进行纵向聚焦.文中首先介绍了方形束团和抛物线形束团的纵向束流动力学,推导了两种束团纵向聚焦所需要的5MHz重复率高压脉冲波形,并给出了实现纵向聚焦的感应腔设计及其特殊要求.     

改进的合肥光源逐束团流强测量方案

 对于多束团运行的储存环，逐束团流强的测量是研究注入填充和束流不稳定性阈值等的重要内容。介绍了加速器常用的一些逐束团监测手段，在此基础上，利用HLS（Hefei Light Source）现有的逐束团测量设备，并配合相应前端信号处理电路，进行了HLS储存环逐束团流强测量。实验线路方面，在传统的高频频率倍频信号检波的基础上，尝试了新的与同步方波信号检波的方法。分别在多束团和单束团情况下对HLS的束团流强进行了连续检测实验，对实验结果进行线性拟合，得到了定标结果，结果表明系统的1阶线性拟合标准偏差均在1%左右；最后对其中非线性部分的物理本质进行了解释。     

合肥电子储存环束流不稳定性的抑制

 合肥光源二期工程改造的电子储存环调试过程中,发现多束团存储和运行时存在耦合束团不稳定性,严重地限制了注入的最高流强,并且影响了光源运行的质量。通过过正地增大正色品以及在储存环上插入八极磁铁,基本上抑制了横向的耦合束团不稳定性,保证了稳定注入束流300 mA的技术指标。     

BEPC横向阻尼时间的测量

 利用逐束团测量系统在BEPC储存环中跟踪单个束团得到其多圈位置振荡信息，获得BEPC储存环的横向阻尼时间与束流流强、色品、八极子和束流能量的关系，并通过分析得到了BEPC储存环辐射阻尼时间为52 ms。实验结果表明：流强越高、色品越大，阻尼率也就越大；束流流强为4.7 mA时八极子强度的变化对阻尼率没有影响；束流流强为5 mA时，阻尼率随束流能量升高而减小。     

电子储存环中离子俘获不稳定性的强-强模型模拟

 电子储存环中,由于被束流势阱俘获的离子会引起束流不稳定性。研究这种不稳定性的产生机制和抑制方法对提高机器的性能有重要理论和现实意义。介绍了用强-强模型对合肥光源（HLS）电子储存环中离子俘获不稳定性产生机制进行的模拟研究。模拟结果可用于理解在合肥光源（HLS）储存环上观察到的离子俘获现象。     

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。     

An experimental study of a new multi-bunch damping mechanism in PETRA

A new damping mechanism of multi-bunch oscillations in a storage ring with help of a narrow-band feedback system has been experimentally tested in PETRA. The oscillations of a multi-bunch filling were sucessfully damped. The bandwidth of the active loop was 1.5 kHz instead of 5 MHz needed for standard damper systems.     

上海同步光源定时系统物理设计

正在建造中的上海光源(SSRF)设计为一台能量为3.5GeV的第三代同步辐射光源, 其定时系统的物理设计使其能够满足储存环的不同运行模式, 如单束团模式、多束团模式、混合模式及Top-up运行模式, 定时系统具有高的稳定性和低的时间晃动. 基于EPICS控制系统的定时系统可提供精确的可编程序事件驱动信号序列, 根据不同需求提供电子枪、调制器、增强器和储存环高频, 注入引出及束测等设备的触发信号.     

Excitation of low-frequency acoustical signals by a vertical array of interacting emitters in oceanic waveguides

We present the results of experiments on the excitation of joint oscillations in a system of electromagnetic emitters submerged in a fluid having the shape of rigid cylinders with ring elastic membranes in the end faces. A mathematical model of the antenna formed by the given set of sound emitters is constructed. Interaction of emitters is considered through the additive pressures exerted on each of the membranes by sound waves excited by neighboring emitters. Variations in pressures of gases filling the cylinders and their influence on oscillations of membranes are also considered. We put forth a system of the integro-differential equations in partial derivatives with decelerations over time describing the forced joint oscillations of emitters. In the harmonic case, solutions to the system are obtained. Numerical calculations are compared with experimental data to verify the model and improve its parameters.     

The Potential-Well Distortion Effect and Coherent Instabilities of Electron Bunches in Storage Rings

The effect of electromagnetic interaction between electron bunches and the vacuum chamber of a storage ring on the longitudinal motion of bunches is studied. Specifically, the potential-well distortion effect and the so-called coherent instabilities of coupled bunches are considered. An approximate analytical solution for the frequencies of incoherent oscillations of bunches distributed arbitrarily within the ring is obtained for a distorted potential well. A new approach to determining frequencies of coherent oscillations and an approximate analytical relation for estimating the stability of a system of bunches as a function of their distribution in the accelerator orbit are presented.     

Coherent interaction of ion and electron beams in systems with electron cooling

A hydrodynamic approximation is used to study the behavior of dipole modes of the transverse oscillations of an ion beam in a storage ring with an electron cooling section. It is shown that in addition to the finite interaction time of the beams, instability may be caused by a specific interaction effect between the ion and electron beams in the magnetic field which leads to redistribution of energy between the various modes of the ion beam oscillations. In this case, the condition that the determinant of the transfer matrix for the cooling section does not exceed unity no longer guarantees the stability of the transverse coherent oscillations of the ion beam and all the eigenvalues of the complete matrix of the ion motion including the storage ring must be analyzed. Calculations of the stability of ion beam dipole oscillations are presented for the parameters of CELSIUS.     

Quantum transport in an H shaped wire and a ring structure

We have numerically studied the transport properties of an H shaped quantum wire structure and a circular quantum ring structure by using the mode matching technique. We have observed that for the H structure, anomalous Hall resistance plateaus exist in relatively low magnetic fields as precursors of integer Hall plateaus. We have found that the resonance patterns of the nonlocal resistance are mainly caused by inter-mode transitions between two highest modes in the system, yielding large oscillations with a mixing frequency in the resistance curve with respect to the width of the bridge-like part of the H structure. For the ring structure, we have found that two oppositely circulating internal waves contribute to the Aharonov-Bohm oscillations, producing beating in the transmission amplitudes.     

Aharonov-Bohm oscillations with spin: evidence for Berry's phase

We report a study of the Aharonov-Bohm effect, the oscillations of the resistance of a mesoscopic ring as a function of a perpendicular magnetic field, in a GaAs two-dimensional hole system with a strong spin-orbit interaction. The Fourier spectra of the oscillations reveal extra structure near the main peak whose frequency corresponds to the magnetic flux enclosed by the ring. A comparison of the experimental data with results of simulations demonstrates that the origin of the extra structure is the geometric (Berry) phase acquired by the carrier spin as it travels around the ring.     

Dispersion management using betatron resonances in an ultracold-atom storage ring

Particles circulating at specific velocities in a storage ring can undergo betatron resonances at which static perturbations of the particles' orbit yield large transverse (betatron) oscillations. We have observed betatron resonances in an ultracold-atom storage ring and found these resonances to cause the near-elimination of the longitudinal dispersion of atomic beams propagating at resonant velocities. This effect can improve atom-interferometric devices. Both the resonant velocities and the resonance strengths were varied by deliberate modifications to the storage ring.     

Optical detection of the Aharonov-Bohm effect on a charged particle in a nanoscale quantum ring

We study spectroscopically the current produced by a charged particle moving in a nanosize semiconductor quantum ring subject to a perpendicular magnetic field. Several Aharonov-Bohm oscillations are observed in the emission of a charged exciton confined in a single ring structure. The magnetic field period of the oscillations correlates well with the size of the rings.     

分离式螺旋热管在蓄冷系统的换热特性分析

阐述了分离式螺旋热管的换热特性,并提出了将螺旋热管应用于蓄冷系统的新方案。建立了分离式螺旋热管的换热模型,分析了热流密度、充液率以及几何尺寸对螺旋热管管内换热的影响,为螺旋热管结构的优化以及在蓄冷系统的应用提供了理论依据。