多条形电极束流能散度探测器的张角优化

 采用Surperfish对北京正负电子对撞机的多条形电极束流能散度探测器进行了电磁场模拟计算。在带模拟束流的情况下,计算分析了探测器对束流位置和能散度的分辨能力与电极张角之间的关系,首次计算了条形电极间的电容耦合综合强度。电极张角优化结果表明：在不考虑噪声水平的情况下,电极张角为20°时,探测器的灵敏度和分辨率达到最优。而当噪声影响很大时,可以适当增加电极张角,同时考虑减小噪声的措施。     

Simulation studies on the polarized positron generation from circularly polarized gamma-rays

Polarized positrons can be generated through the electron-positron pair creation from circularly polarized gamma-rays hitting a conversion target. Laser-Compton scattering is an efficient method to generate circularly polarized gamma-rays. Simulation studies on these two processes have been done with the Monte Carlo codes, CAIN and GEANT4. Using CAIN to simulate the Laser-Compton scattering process, the energy spectrum of the generated polarized photons could be obtained. GEANT4 was used to study the yield, energy spectrum and the mean polarization of the positrons emanating from the conversion target. To increase the yield of the generated positrons, an optimization study on the thickness of conversion target was also performed.     

Transverse profile expansion and homogenization at target for the injector Scheme-I test stand of China-ADS

For the injector Scheme- test stand of the China-ADS(Accelerator Driven subcritical System), a beam with the maximum power of 100 k W will be produced and transported to the beam dump. To solve the very high thermal load problem at the dump, two measures are taken to deal with the huge power density at the target.One is to enlarge the contact area between the beam and the target, and this is to be accomplished by expanding the beam profile at the target and using slanted target plates. The other is to produce a more homogenous beam profile at the target to minimize the maximum power density. Here the beam dump line is designed to meet the requirement of beam expansion and homogenization at 3 different energies(3.2 Me V, 5 Me V and 10 Me V), and the step-like field magnets are employed for the beam spot homogenization. Taking into account the fact that the space charge effects are very strong at such low beam energies, the simulations have included space charge effects and errors which show that the beam line can meet the requirements very well. In the meantime, the alternative beam design using standard multipole magnets is also presented.     

S波段6 MeV边耦合电子直线加速器的设计研究（英）

近年来,对紧凑、稳定及可靠型电子直线加速器的需求越来越多,其能量主要分布在几百keV到十几个MeV的范围内,其中需求最多的则是能量在MeV量级的微波电子直线加速器。在这种形势下,中国科学院高能物理研究所正在研制一台S波段6 MeV的边耦合电子直线加速器,本文对基于该加速器的模拟计算研究进行了介绍。EGUN和HFSS分别用来设计电子枪和边耦合加速结构。通过将EGUN计算得到的电子束流参数和HFSS计算得到的三维电磁场分布数据引入到PARMELA中,完成了对该加速器的多粒子动力学研究。模拟结果显示,所设计的加速器完全能够满足设计指标的要求。最终,在考虑束流负载效应的因素后,完成了边耦合加速结构的微波结构设计。     

BEPCII次谐波聚束系统物理公差要求的研究

为了进一步提高束流品质并逐步采用双束加速技术, BEPCII直线加速器准备采用带有两个次谐波聚束器的双次谐波聚束系统。目前, 该次谐波聚束系统的物理设计和优化已经基本完成。由于新设计的双次谐波聚束系统很不同于BEPCII现有的聚束系统, 因此, 就要求对聚束系统中存在的各种抖动(jitter)效应重新进行研究。 使用多粒子模拟计算程序PARMELA对电子枪的高压抖动和定时抖动、次谐波聚束器的相位抖动以及功率抖动、聚束器中加速电场相位以及A0加速管(俘获加速节)中加速电场相位的抖动等效应进行了研究, 并最终确定了聚束系统中各部件的物理公差要求。     

BEPCII Injector Linac Upgrade and Beam Instabilities

The upgrade project of the Beijing Electron Positron Collider （BEPCII） and its injector linac is working well. The linac upgrade aims at a higher injection rate of 5OmA/min into the storage ring, which requires an injected beam with low emittance, low energy spread and high beam orbit and energy stabilities. This goal is finally reached recently by upgrading the linac components and by dealing with rich and practical beam physics, which are described in this study.     

Design and studies on the traveling wave transverse RF deflecting structure

With the development of free electron laser (FEL) and the international linear collider (ILC), the electron bunch length is getting smaller and smaller. The traveling-wave transverse RF deflecting structure is an important part of the RF deflecting method for bunch length measurement and phase space diagnostics. The operation mode in RF deflector is the ``TM₁₁-like' mode. Since the TM₁₁-like mode in this structure has a pair of degenerate dipole modes, two additional holes are provided on either side of each iris to stabilize the mode. The simulation and optimization have been done. A prototype has been fabricated and tested. The cold test results have been compared with the simulations of the first three modes.     

Progress on the construction of the 100 MeV/100 kW electron linac for the NSC KIPT neutron source

IHEP, China is constructing a 100 MeV/100 kW electron Linac for NSC KIPT, Ukraine. This linac will be used as the driver of a neutron source based on a subcritical assembly. In 2012, the injector part of the accelerator was pre-installed as a testing facility in the experimental hall ≠2 of IHEP. The injector beam and key hardware testing results met the design goal. Recently, the injector testing facility was disassembled and all of the components for the whole accelerator have been shipped to Ukraine from China by the ocean shipping. The installation of the whole machine in KIPT will be started in June, 2013. The construction progress, the design and testing results of the injector beam and key hardware are presented.     

RF thermal and new cold part design studies on a TTF-Ⅲ input coupler for Project-X

An RF power coupler is one of the key components in a superconducting (SC) linac. It provides RF power to the SC cavity and interconnects different temperature layers (1.8 K, 4.2 K, 70 K and 300 K). The TTF-Ⅲ coupler is one of the most promising candidates for the High Energy (HE) linac of Project X, but it cannot meet the average power requirements because of the relatively high temperature rise on the warm inner conductor, so some design modifications will be required. In this paper, we describe our simulation studies on the copper coating thickness on the warm inner conductor with RRR values of 10 and 100. Our purpose is to rebalance the dynamic and static loads, and finally lower the temperature rise along the warm inner conductor. In addition, to get stronger coupling, better power handling and less multipacting probability, one new cold part design was proposed using a 60 mm coaxial line; the corresponding multipacting simulation studies have also been investigated.     

作为BEPCII预注入器的光阴极注入器

 为了提高并且采用双束加速技术以进一步提高BEPCII正电子从直线加速器注入到储存环的速率,BEPCII(Beijing Electron Positron Collider Upgrade Project) 正在建造带有两个次谐波聚束腔的新预注入器。提出了使用光阴极注入器作为BEPCII预注入器的新方案,其性能优于次谐波聚束系统：发射度和能散至多为次谐波聚束系统的1/4,100%的传输效率,没有卫星束团的干扰,等。此外,还分别对光阴极注入器在高电荷量和低电荷量两种情况下的束流动力学进行了模拟计算和优化研究,并将其性能与正在建造的次谐波聚束系统和旧聚束系统的性能进行了比较和讨论。由此光阴极注入器产生的电子束还可以在将来用作激光-等离子体或激光-非传导性加速结构的尾场加速研究。