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。     

HT-6M托卡马克装置杂质输运

利用多道可见光谱探测系统和近紫外转镜系统测量了HT-6M托卡马克等离子体中杂质的时空分布.建立完备的杂质输运程序，数值模拟碳、氧杂质在欧姆放电时的输运行为，得出了杂质的扩散和对流系数、不同电离态杂质离子密度、辐射功率密度和有效电荷数的空间分布. 分析低混杂波电流驱动（LHCD）期间杂质行为，结果表明等离子体粒子约束、杂质约束和能 量约束提高，辐射功率和有效电荷数减小. 关键词： 托卡马克 杂质输运 扩散系数 对流系数     

氩气介质阻挡放电不同放电模式的电学特性研究

采用水电极介质阻挡放电装置，在气压为40kPa的氩气中实现了弥散、流光和斑图三种不同 模式的放电，并对其光电特性进行测量.通过测量测试电容上的电压，从而将气隙电压计算 出来，发现随外加电压增加，放电起始时刻不断提前，放电占空比增加；对应放电时刻，气 隙电压减小、输运电荷突增，使得气隙电压和电量波形都远远偏离正弦.气隙电压与输运电 荷成非线性关系.给出了外加电压零点对应的气隙电压随外加电压峰值的变化关系.讨论了壁 电荷在放电中的作用及对气隙电压和电量波形的影响. 关键词： 介质阻挡放电 气隙电压 自组织斑图 输运电荷     

HL-2A装置上的极向电荷交换复合光谱诊断

介绍了HL-2A装置上的高时空分辨极向电荷交换复合光谱诊断系统。该系统观测范围覆盖了大半径R=1.91~2.02m的等离子体区域,通过测量碳杂质离子谱线CⅥ(n=8→7,λ=529.06nm)的多普勒展宽,获得离子温度的分布剖面。该系统共有2个光学采集透镜组,其中一个透镜组放置在中性束注入窗口附近,用于观测中性束注入时的主动光谱和被动光谱;另一个透镜组放置在装置的另一侧,用于观测被动光谱。为了实时准确地对各测量通道的波长进行监测,采用了波长λ=532nm的激光作为参考。在有中性束注入的高模放电期间,系统在等离子体边界R~2.00m的位置观测到显著的边缘输运垒。     

基于积分束流变压器的加速器束团电荷量测量系统

 为满足清华大学加速器实验室光阴极微波电子枪实验平台的发展需求，设计了束团电荷量测量系统，可以实现实时测量加速器束团电荷量的目标。这套测量系统基于积分束流变压器，包括前置放大器、门控积分器、模数转换和数据传输模块。利用信号发生器模拟束流，对整套系统进行了离线测量实验。当前置放大器放大倍数取200和20时，AD转换值和束流电荷的比值分别为2.181 PC-1和0.195 PC-1，与理论值2.070 PC-1和0.207 PC-1基本吻合；其对应的电荷量测量误差分别小于2 PC和15 PC。测量结果和模拟束流电荷量值的拟合曲线线性度好，相关系数的平方均大于0.999 0。该结果验证了系统的可行性。     

HL-2A 装置上的极向电荷交换复合光谱诊断

介绍了HL-2A 装置上的高时空分辨极向电荷交换复合光谱诊断系统。该系统观测范围覆盖了大半径R=1.91~2.02m 的等离子体区域,通过测量碳杂质离子谱线CⅥ(n=8→7,λ=529.06nm)的多普勒展宽,获得离子温度的分布剖面。该系统共有2 个光学采集透镜组,其中一个透镜组放置在中性束注入窗口附近,用于观测中性束注入时的主动光谱和被动光谱;另一个透镜组放置在装置的另一侧,用于观测被动光谱。为了实时准确地对各测量通道的波长进行监测,采用了波长λ=532nm 的激光作为参考。在有中性束注入的高模放电期间,系统在等离子体边界R~2.00m 的位置观测到显著的边缘输运垒。     

国外物理科普杂志精文提要

 H.谢尔等《输运和弛豫出的时标不变性》1月号在许多无序材料中看到标度不变动力学现象.分散运动可定量解释非晶半导体和绝缘体、聚合物薄膜、分子固溶体和玻璃等材料输运和迁移的测量中的普遍特性.文章讨论无序半导体中的电荷输运,论及它的实验和机制、弛豫规律.最后讨论玻璃材料中的弛豫.由上可见,无序系统中的输运和弛豫特性可归因于事例间时间的长尾分布,而这一分布限制了运动.     

α—LiIO_3准一维离子电导空间电荷沉积线的直观显示

为了研究α-LiIO_3在直流电场作用下,离子输运与其光学、电学性质的关系,我们设计并完成了电荷沉积线的静电染色显示和针状电极作用下电荷沉积线的生长与分布情况的光学观测实验。直接显示出间隙Li~=和Li空位都存在各自的沉积线,证实了我们以前报道的光栅亮线是带电荷的实体;整个生长层为富集Li~+区;直观地证实了α-LiIO_3离子管道输运与电荷沉积是完全一致的和α-LiIO_3的准一维电导特性。     

高能同步辐射光源直线加速器初期调束取得重要进展

高能同步辐射光源（HEPS）是中国第一台第四代高能同步辐射光源,其加速器由直线加速器、增强器、储存环及输运线组成。报道了HEPS直线加速器的初期束流调试重要进展。HEPS直线加速器是一台500 MeV S波段常温直线加速器,由热阴极电子枪、聚束系统、主直线加速器构成。在按时完成设备加工、安装和老练的基础上,于2023年3月9日启动束流调试,当天实现束流全线贯通。3月14日束流能量达到500 MeV,束团电荷量达到2.5 nC。经过测量,直线加速器出口束流能散0.4%,能量稳定度0.06%,水平和垂直几何发射度分别为233 nm和145 nm。目前直线加速器束团电荷量可达到7.0 nC,相关束流调试正在进行。     

超导体电输运及交流磁化率双模式测量系统研制

介绍了一种基于小型制冷机的超导转变温度电输运和交流磁化率双模式单腔测量装置。该装置包括电输运法测量和交流磁化率法测量两部分,分别实现对高温超导薄膜样品的超导转变温度的测量。电输运法测量部分利用四点法测量原理对超导薄膜的电阻进行测量,获取电阻随温度变化的曲线;同时利用电流换向法消除热电势带来的测量误差,以进一步提高测量的精度。交流磁化率法测量部分利用的是电磁感应原理和超导磁效应。该部分包含有初级线圈和次级线圈,超导样品放置于两线圈之间。初级线圈用于产生交变激励磁场,次级线圈的输出信号反应了超导样品磁化率的变化,其输出信号由锁相放大器获取。测量过程中使用计算机自动记录测量数据。     

Bunch length measurement using a traveling wave RF deflector

RF deflectors can be used for bunch length measurement with high resolution. This paper describes a completed S-band traveling wave RF deflector and the bunch length measurement of the electron beam produced by the photocathode RF gun of the Shanghai DUV-FEL facility. This is the first time that such a transverse RF deflector has been developed and used to measure the bunch length of picosecond order in China. The deflector's VSWR is 1.06, the whole attenuation 0.5 dB, and the bandwidth 4.77 MHz for VSWR less than 1.1. With a laser pulse width of 8.5 ps, beam energy of 4.2 MeV, and bunch charge of 0.64 nC, the bunch lengths for different RF input power into the deflector were measured, and an averaged rms bunch length of 5.25 ps was obtained. A YAG crystal is used as a screen downstream of the deflector, with the calibrated value of 1 pix = 136 μm.     

HLS bunch current measurement system

Bunch current is an important parameter for studying the injection fill-pattern in the storage ring and the instability threshold of the bunch, and the bunch current monitor also is an indispensable tool for the top-up injection. A bunch current measurement (BCM) system has been developed to meet the needs of the upgrade project of Hefei Light Source (HLS). This paper presents the layout of the BCM system. The system based on a high-speed digital oscilloscope can be used to measure the bunch current and synchronous phase shift. To obtain the absolute value of bunch-by-bunch current, the calibration coefficient is measured and analyzed. Error analysis shows that the RMS of bunch current is less than 0.01 mA when bunch current is about 5 mA, which can meet project requirement.

     

Simulation study of electron injection into plasma wake fields by colliding laser pulses using OOPIC

An electron injector concept for a laser-plasma accelerator has been developed which relies on the use of counter propagating ultrashort laser pulses. In this paper, we use OOPIC the fully self-consistent, twodimensional, particle-in-cell code to make a parameter study to determine the bunches that can be obtained through collisions of two collinear laser pulses in uniform plasma. A series of simulations show that one can obtain a short (<10fs) bunch with its charge of about 15pC, and energy spread of about 15%. We also discussed the variation of the transverse spot size of the electron bunch and found the bunch would undergo the betatron oscillations.     

北京大学DC-SC光阴极注入器的升级设计

 基于直流电子枪-超导加速腔（DC-SC）光阴极注入器样机的初步实验结果，北京大学提出了新的注入器的改进设计。新注入器核心结构包括皮尔斯枪和3+1/2超导腔。文章给出了它们的详细结构参数，然后采用程序，对注入器的束流动力学进行了模拟。结果发现：新注入器可以提供具有高束流品质、高平均流强的电子束，束团的电荷量100 pC，横向发射度低于2 mm·mrad,脉宽5 ps,rms束斑可达0.5 mm，重复频率81.25 MHz；也可以提供电荷量为300 pC低重复频率的高峰值流强的电子束，其横向发射度小于3 mm·mrad,脉宽约为9 ps，以满足北京大学自由电子激光（PKU-FEL）实验平台的要求。     

Transition radiation from an extended bunch of charged particles

The spatial distribution of the transition radiation generated by an extended system of charges is studied. The charges sequentially cross the interface at equispaced points. Also, the transition from a spherical bunch with the uniform charge distribution is considered. The radiation patterns produced by the point charge and by the bunch of the charges are shown to differ significantly at certain sizes of the bunch expressed in terms of the wavelength. Charge distributions such that the transition radiation exhibits the properties typical of the Doppler effect or of Vavilov-Cherenkov radiation are found to be possible.     

束团磁压缩的高阶限制

研究了束团压缩中的高阶效应, 结果表明存在高阶项的压缩限制, 压缩后束团的长度比线性理论值长, 初始为均匀分布的束团较高斯分布更易压缩, 在相同的加速段与磁压缩器条件下, 其所获得的束团长度较短, 最后作了数值计算, 结果与理论相符.     

Theoretical study of a dual harmonic system and its application to the CSNS/RCS

Dual harmonic systems have been widely used in high intensity proton synchrotrons to suppress the space charge effect,as well as reduce the beam loss.To investigate the longitudinal beam dynamics in a dual rf system,the potential well,the sub-buckets in the bunch and the multi-solutions of the phase equation are studied theoretically in this paper.Based on these theoretical studies,optimization of bunching factor and rf voltage waveform are made for the dual harmonic rf system in the upgrade phase of the China Spallation Neutron Source Rapid Cycling Synchrotron(CSNS/RCS).In the optimization process,the simulation with space charge effect is done using a newly developed code,C-SCSIM.     

Design of BEPC Ⅱ bunch current monitor system

BEPC Ⅱ is an electron-positron collider designed to run under multi-bunches and high beam current condition. The accelerator consists of an electron ring, a positron ring and a linear injector. In order to achieve the target luminosity and implement the equal bunch charge injection, the Bunch Current Monitor (BCM)system is built on BEPC Ⅱ. The BCM system consists of three parts: the front-end circuit, the bunch current acquisition system and the bucket selection system. The control software of BCM is based on VxWorks and EPICS. With the help of BCM system, the bunch current in each bucket can be monitored in the Central Control Room. The BEPC Ⅱ timing system can also use the bunch current database to decide which bucket needs to refill to implement "top-off" injection.     

Generation of 0.1 THz coherent synchrotron radiation with compact S-band linac at AIST

The 0.1 THz coherent synchrotron radiation (CSR) was successfully generated in the 90° bending magnet of the compact S-band linac with the achromatic arc section using the ultra-short electron bunch which has the energy of 40 MeV, the bunch charge of about 1nc and the bunch length less than 1 ps (rms). The electron bunch compression of 1 nC electron bunch was achieved less than 1 ps (rms) by controlling the Q-magnets in the achromatic arc section as the bunch length was measured by the rms bunch length monitor.