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.     

BEPCⅡ中电子云密度的计算研究

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,区别于国外的研究编写发展了模拟计算程序,首次给出了前室型真空管道中电子云的聚集情况,定量计算了不同前室长度,不同二次电子产额作用下的电子云密度;通过模拟计算研究了在真空管道中放置清洗电极来降低电子云密度并改变密度分布以抑制不稳定性的可能性,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     

北京正负电子对撞机中的束流光电子不稳定性研究

高能储存环中的正电子束流辐射出光子,打在束流管道壁上产生光电子并形成电子云;多束团正电子束流与电子云相互作用,有可能发生的不稳定性,称为束流光电子不稳定性.这种不稳定性有可能在下一代高能正负电子对撞机的束流中发生,因此对这种束流不稳定性的研究,也有很重要的实际意义.文章讨论了在北京正负电子对撞机(BEPC)上开展的束流光电子不稳定性实验和模拟分析研究.     

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.     

多束团不稳定性的模拟研究

利用模拟的方法研究了多束团不稳定性.SCBI程序(SIMULATION OF COUPLED-BUNCH INSTABILITIES)是一个用来模拟研究储存环上高频腔、真空盒内壁及其它腔形结构元件的长程尾场和中程尾场激发的多束团不稳定性的综合程序.在束团均匀分布情形下,比较了SCBI程序与ZAP程序的结果,两者非常一致.同时,利用SCBI程序对北京正负电子对撞机(BEPC)多束团改进方案(BEPCⅡ)的多束团不稳定性进行了详细的研究.     

多粒子模拟方法分析北京正负电子对撞机储存环束团长度拉伸效应

采用多粒子模拟方法,分析了北京正负电子对撞机(BEPC)储存环纵向不稳定性,给出了BEPC储存环束团长度与单束流强的关系,得出了阈值流强.模拟结果与BEPC95年4月实测结果符合较好.     

BEPCⅡ直线加速器中的束流轨道和能量稳定性的研究

在BEPCⅡ直线加速器的调试和初期运行中, 观察到束流轨道和能量的不稳定性. 本文通过实验测量和分析研究, 说明了这些不稳定性的原因, 并叙述了解决这些不稳定性的方法和改进结果.     

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.     

BEPC上离子引起的耦合束团不稳定性分析

对在北京正负电子对撞机(BEPC)上观测到的由离子引起的电子束二极耦合束团不稳定性的实验数据作了分析处理,给出了这种二极耦合束团不稳定性的边带.首先用离子俘获的线性两束流理论定量计算了离子引起的二极耦合束团不稳定性发生的阈值束流流强和不稳定性的增长时间,然后用基于束流–离子强弱作用模型的模拟程序跟踪了在实验情况下束流与离子的相互作用过程,跟踪结果成功地再现了离子引起的二极耦合束团不稳定性边带,并给出了比较合理的不稳定性增长时间.     

北京正负电子对撞机束团拉伸效应研究

本文叙述了在北京正负电子对撞机(BEPC)上,用条纹相机和频谱分析方法对束团拉伸效应的研究.由测量结果归纳出BEPC束团拉伸效应的标度规律,这一规律与理论分析有相当好的一致关系.     

Studies on electron cloud instability in BEPCⅡ

Electron Cloud Instability has been studied in the operation of BEPC. The BEPCⅡ began the commissioning in November 2006 and the positron beam current has reached 500 mA. Because of such a high beam current, some instabilities such as ECI, bunch lengthening et al, have appeared during the operation. The experimental investigation on ECI during the commissioning of BEPCⅡ will be reported in this paper.     

Electron Cloud Instability Simulation Studies for BEPCⅡ

Electron cloud instability (ECI) may take place in a storage ring when the machine is operated with multi-bunch positively charged beam. According to the actual shape of vacuum chamber in BEPCⅡ, a computer simulation program has been developed. With the code, the electron density in the chamber with the different widths of antechamber and the different secondary electron yields, respectively, can be obtained. The possibility to put clearing electrodes in the normal chamber or ante-chamber to reduce the electron density in the central region of the chamber is also investigated. In the simulation, the coherent oscillation of bunches and the formation of electron cloud (EC) are tracked simultaneously. The sideband distribution and growth rate can be obtained through tracking and dealing the bunch oscillation amplitude with FFT. Based on the head-tail model, the single bunch instability induced by EC is also studied. By the simulation, for BEPCⅡ the threshold density for the single bunch instability is estimated to be～10 12 m -3 and the restraining measures that might be adopted in BEPCⅡ can control the EC density under the threshold. According to the simulation results, a relatively big positive chromaticity should be used to suppress the bunch blow up.     

Progress of the Injector Linac Upgrade for the BEPCⅡ Project

BEPCⅡ—an upgrade project of Beijing Electron Positron Collider (BEPC) is a factory type of e+e- collider. It requires its injector linac to have a higher beam energy (1.89 GeV) for on-energy injection and a higher beam current (40 mA e+ beam) for a higher injection rate ( 50 mA/min). The low beam emittance (1.6π mm·mrad for e+ beam, and 0.2πmm·mrad for 300 mA e- beam) and the low beam energy spread (±0.5%) are also required to meet the storage ring acceptance. Thus the original BEPC injector linac must be upgraded to have a new electron gun with its complete tuning system, a new positron source with a flux concentrator, a new RF power system with its phasing loops and a new beam tuning system with orbit correction and optics tuning devices. These new components have been designed, fabricated, tested and will be installed in their final positions in this spring and summer, which are described in this paper.     

Beam dynamics studies on BEPC-Ⅱstorage rings at the commissioning stage

During the 1st and 2nd stages of the commissioning of the upgrade project of the Beijing Electron Positron Collider(BEPC Ⅱ),which started on Nov.12,2006 and Oct.24,2007,respectively,we got the luminosity one tenth of its design value,provided beams to synchrotron radiation users for about 4 months,and studied beam dynamics as well.In this paper,some beam dynamics studies on the storage rings and their preliminary results are given.     

BEPCⅡ直线加速器的双脉冲加速研究

 为了将BEPCⅡ直线加速器的正电子注入速率提高到单脉冲运行时的两倍左右, 提出了双脉冲产生和加速的方案。对BEPCⅡ直线加速器双脉冲加速的束流动力学进行了模拟, 首次给出了双脉冲的模拟方法。此外, 还在BEPCⅡ直线加速器上进行了双脉冲加速的初步实验研究, 为以后BEPCⅡ直线加速器的进一步改造提供了参考。     

Design and simulation of the wire scanner for the injector linac of BEPC Ⅱ

BEPC Ⅱ,the upgrade project of Beijing Electron Positron Collider (BEPC),is an accelerator with large beam current and high luminosity,so an efficient and stable injector is required.Several beam diagnostic and monitoring instruments are used.A new diagnostic instrument--wire scanner,has been designed and will be used to nleasure the profile of the linac beam of BEPC Ⅱ.This paper describes the prototype of this system and the cause of heat generating of the wire.Some simulation results of the heat and force by using finite element method software-ANSYS(R),2) are presented and discussed.     

BEPCⅡ Positron Source

BEPCⅡ— an upgrade project of the Beijing Electron Positron Collider (BEPC) is a factory type of e^＋e^－ collider. The fundamental requirements for its injector linac are the beam energy of 1.89GeV for on-energy injection and a 40mA positron beam current at the linac end with a low beam emittance of 1.6μm and a low energy spread of ±0.5% so as to guarantee a higher injection rate (≥50mA/min) to the storage ring. Since the positron flux is proportional to the primary electron beam power on the target, we will increase the electron gun current from 4A to 10A by using a new electron gun system and increase the primary electron energy from 120MeV to 240MeV. The positron source itself is an extremely important system for producing more positrons, including a positron converter target chamber, a 12kA flux modulator, the 7m focusing module with DC power supplies and the support. The new positron production linac from the electron gun to the positron source has been installed into the tunnel. In what follows, we will emphasize the positron source design, manufacture and tests.     

BEPC储存环束流振荡频率测量

在加速器的运行和机器研究过程中,需要经常对束流振荡频率进行测量.BEPC储存环束流振荡频率测量系统包括一台频谱仪,两个条形电极装置,两个电压放大器和一个束流振荡检测器.本文介绍了经过改进的BEPC储存环束流振荡频率测量系统.