First experimental research of the bunch compressor at CAEP

Magnetic bunch compressor is one of the key technologies on the path to next generation accelerator driven facilities. In this paper we report the design principles and the first experimental research of the bunch compressor developed at Chinese Academy of Engineering Physics （CAEP）. The length of the bunch after compressor is found to be about 0.7 ps （rms） and the peak current exceeds 500 A when operated in the optimized condition. The sensitivity of the bunch length on the phase of the acceleration field and magnetic field of the bunch compressor was also measured and analyzed.     

Magnetic Properties and Magnetoresistance of CdMnS：Au Based Structures Prepared by Co-evaporation

Polycrystalline CdMnS and CdMnS：Au films with hexagonal structure on Si（111） substrates are prepared by co-evaporation, and exhibit ferroelectric and ferromagnetic properties, respectively. Under optimized growth conditions, CdMnS：Au samples with an average crystallite size of 90nm and Mn concentration of 5.0at.% are obtained, and an all-semiconductor spin valve device of Co/Au/CdMnS：Au/CdMnS/Pt is fabricated. Electrical measurement of the device reveals the clear dependence of resistance on applied magnetic field, with a relative magnetoresistance of 0.06% and a switching field of 100 Oe at 77K.     

基于束流位置探测器的束团长度测量

分析了驱动电子束团的频域特性,研究了基于该特性进行长度测量的理论基础;使用三维模拟软件对束流位置探测器(BPM)进行建模,用模拟的方法对传输阻抗进行了数值计算;对不同长度的束团进行了测量和计算,并且分析了束团位置在真空管道中偏移对束团长度测量的影响。由测量结果可见,电子束团长度在10~100 ps(3~30 mm)时,测量误差均小于2%,满足中国工程物理研究院高平均功率自由电子激光太赫兹实验测量的使用要求。     

中波红外3 μm～5 μm宽带通滤光片的研制

 中波红外宽带通滤光膜通常膜系层数多,膜层总厚度非常大（厚度达到10 μm左右）,膜层的镀制工艺难度较大。通过分析红外带通滤光片几种设计方法的特点,并结合实际镀制工艺技术,采用了长波通与短波通及非规整薄膜设计技术相结合的方法,设计了以锗材料为基底的中波3 μm～５ μm宽带通滤光膜。该设计大幅度降低了膜层的总厚度（约为8.65 μm）,缩短了膜层的镀制周期,提高了膜层的牢固度;在膜层的镀制工艺过程中,通过改变薄膜材料的蒸发速率、修正蒸发硫化锌材料时电子枪的扫描方式、调整蒸发材料在坩埚中的装载方法,使膜层获得了优异的光谱性能,其通带平均透过率大于96%,截止区域的平均透过率小于1%。     

Design study of an improved laser wire system for electron beam measurement

The laser wire (LW) method has been demonstrated to be an effective non-interceptive technique for measuring transverse profile and emittance of electron beams in colliders, storage rings and dumping rings. In this paper, we present an improved design of high repetition LW system for high average power free electron lasers (HAP FELs) and energy recovery linacs (ERLs). This improved LW utilizes the excess power of the photocathode drive laser, thus making itself much cheaper and simpler. The system main parameters are optimized with numerical calculations and Monte Carlo simulations, indicating that resolutions would be better than 100 μm and scanning time less than 1 minute. Status of the experiment preparation is also presented.     

Self-Injection and Acceleration of Monoenergetic Electron Beams from Laser Wakefield Accelerators in a Highly Relativistic Regime

Self-injection and acceleration of monoenergetic electron beams from laser wakefield accelerators are first investigated in the highly relativistic regime, using 100 TW class, 27 fs laser pulses. Quasi-monoenergetic multi- bunched beams with energies as high as multi-hundredMeV are observed with simultaneous measurements of side-scattering emissions that indicate the formation of self-channelfing and self-injection of electrons into a plasma wake, referred to as a ＇bubble＇. The three-dimensional particle-in-cell simulations confirmed multiple self-injection of electron bunches into the bubble and their beam acceleration with gradient of 1.5 GeV/cm.     

基于氨基酸位置特异性的蛋白质Loop区结构预测改进方法

蛋白质loop区的结构预测是理解蛋白质功能的重要一环,而长loop区的结构预测至今还是生物信息学中的难题.目前己经出现了多种loop结构的算法,其中LEAP是预测精度最高的算法之一,但它在长loop区初始主链构象采样上仍有较大的改进余地.本文中我们将蛋白质二级结构预测算法SPINE X与LEAP算法结合起来,构建了新的主链扭转角分布图(拉氏图),在主链初始构象采样中引入氨基酸在蛋白序列中的位置特异性信息,使得初始构象的采样更具针对性,对取自CASP10单链蛋白的loop测试集的分析表明,对长度为10,11,12个氨基酸的长loop区,改进后算法都比原始LEAP算法的预测精度有显著提升.这种引入氨基酸位置特异性从而提高预测精度的思路有望进一步推广至loop结构预测的其他算法.     

苯乙烯-甲基丙烯酸甲酯嵌段共聚物的合成与表征

采用阴离子聚合技术合成了一系列苯乙烯-甲基丙烯酸甲酯的两嵌段共聚物(PS－b－PMMA)．采用GPC、FTIR、NMR(¹HNMR、¹³CNMR和固体NMR)和DMA等手段进行了表征．结果表明,所得产物为高分子量、窄分布、具有微相分离结构的两嵌段共聚物．     

反斯托克斯拉曼光谱在BaTiO_3铁电相变研究中的应用

从理论上讨论了一阶和二阶斯托克斯与反斯托克斯拉曼散射截面的温度依赖关系;在２９３Ｋ至４０１Ｋ的温度范围内,测量了ＢａＴｉＯ３单晶斯托克斯和反斯托克斯过程的偏振拉曼光谱;通过对ＢａＴｉＯ３单晶斯托克斯和反斯托克斯拉曼光谱的综合分析,证实在Ｘ（ＺＺ）Ｙ几何配置下测量到的位于２７５和５１４ｃｍ－１处的强峰为一阶拉曼光谱。此结果支持了ＢａＴｉＯ３铁电相变机制的有序—无序模型。     

低反轰多腔热阴极微波电子枪物理设计

 为了开展基于自由电子激光的紧凑型太赫兹源技术研究,获得高品质（强流、低能散、低发射度）电子束,提出了一个低反轰双路微波馈入多腔热阴极微波电子枪的设计方案。用两路独立微波馈入激励微波电子枪,一路由首腔馈入激励首腔和实现阴极表面建场引出电子,另一路由后续腔馈入并通过腔间耦合激励各腔。两路微波互不耦合,通过移相器实现首腔和第2腔之间的相移连续可调。理论模拟结果表明:在一个射频周期内,热阴极微波电子枪的电子反轰功率约8 kW,平均反轰功率仅为1.2 W（重复频率25 Hz和脉宽6 μs）。