10 MeV同轴腔电子加速器辐射屏蔽设计

中国科学院近代物理研究所自主研制了一台同轴腔电子加速器,能产生10 MeV,10 mA的辐照电子束,建成后有望成为我国首台国产化的花瓣形电子辐照加速器。为保证该装置运行时的辐射安全,为今后同类型装置的辐射屏蔽设计提供参考,对该加速器开展了辐射屏蔽研究。首先结合装置的使用情况给出了一种地上为主机室地下为辐照室的半地下机房结构,然后采用蒙卡程序FLUKA计算了相关墙体的厚度。在蒙卡计算中,基于同轴腔加速器的束流损失特点,建立了适用于该类型装置的蒙卡源项输入模型,充分考虑了决定辐射场的主要束损点,同时设置相对简单。结果表明:在设定的屏蔽外剂量率目标下,以普通混凝土作为屏蔽材料,主机室的侧墙、顶板和辐照室顶板的厚度分别需要160～220,110～150,150 cm。     

ILC正电子源靶接触热传导冷却技术的初步研究

国际直线对撞机（ILC）正电子靶沉积的热功率将超过20 kW,传统的冷却方式已无法满足要求。美国Argonne国家实验室提出了摩擦接触热传导冷却的方法。根据Argonne实验室的研究方案,设计了一种旋转摩擦接触冷却的简化装置,根据热传导理论,结合ANSYS软件模拟了旋转冷却过程中的温度分布,理论上验证了方法的可行性。按照模拟的参数和结果,进行了摩擦接触热传导冷却实验,通过实验结果和数据分析证实了,低温区（20℃~50℃）有良好的冷却效应,初步验证了摩擦接触热传导冷却方案的有效性。A new scheme that cooling international Linear Collider (ILC) positron source target by touching thermal conduction (TTC) is presented by Argonne National Laboratory (ANL).Recent results of simulation for cooling the iron targets with 300 and 450 W heat reservoir by ANSYS and experiment of cooling the iron target with 300 and 450 W friction heat reservoir at Institute of Modern Physics (IMP),Chinese Academy of Sciences (CAS),have proved that the TTC has good cooling effect in low temperature zone (20℃~50℃),and preliminarily verified the feasibility of TTC for cooling the ILC positron source target.     

基于混合Copula模型的投资组合风险分析

金融市场或股票之间的相关关系变化灵活多样,针对现实中往往需要考虑的是多个市场、股票的结构,采用Mixture-Copula模型来分析多元市场的相关性结构,进而构建了Multivariate-GARCH-Mixture-Copula,模型,并选取2002年1月1日至2011年12月31日上证工业指数、商业指数、地产指数三个行业指数序列的2425组数据利用该模型进行实证分析.分析表明,Multivariate-GARCH-Mixture-Copula模型能有效地应用于实际金融市场潜在结构的分析,对投资组合的风险研究有一定的参考意义.     

用观察法求二阶变系数齐线性方程的非零特解

主要用观察法求二阶变系数齐线性方程的非零特解.首先推广了欧拉方程和另外一个关于求非零特解的结论,其次在已有结果的情形外增添一些可用观察法求特解的情形.     

Areal density and spatial resolution of high energy electron radiography

Ultrafast imaging tools are of great importance for determining the dynamic density distribution in high energy density(HED) matter. In this work, we designed a high energy electron radiography(HEER) system based on a linear electron accelerator to evaluate its capability for imaging HED matter. 40 MeV electron beams were used to image an aluminum target to study the density resolution and spatial resolution of HEER. The results demonstrate a spatial resolution of tens of micrometers. The interaction of the beams with the target and the beam transport of the transmitted electrons are further simulated with EGS5 and PARMELA codes, with the results showing good agreement with the experimental resolution.Furthermore, the experiment can be improved by adding an aperture at the Fourier plane.     

高能电子成像暗场成像技术特性研究及改进方案

基于EGS5与PARMELA模拟软件组成的高能电子成像系统，对暗场成像的模拟研究发现，通过调节光阑位置实现的暗场成像结果存在失真现象。针对该失真现象提出的改进方案，消除了暗场成像结果的失真。通过对40 MeV电子透射7~224 μm的铝样品开展的成像模拟结果表明:40 MeV高能电子暗场成像技术在铝样品厚度小于25 μm情况下具有明显的面密度分辨优势，且空间分辨率达到μm量级，非常适用于高能量密度物质诊断。     

325 MHz微波栅控高压型热阴极电子枪的设计研究

高重复频率、高平均流强的电子枪具有十分广泛的应用。设计了一台束团重复频率为325 MHz在CW模式工作的微波栅控高压型热阴极电子枪,并详细论述了该类型微波栅控电子枪的实验原理。在该类型电子枪的设计中,首先需要利用仿真模拟软件EGUN、POISSON（PoissonSuperfish）、GPT（General Particle Tracer）完成300 kV直流高压电子枪的结构设计,并进行束流动力学验证计算。为将微波馈入该直流电子枪的阴栅极之间,进行了该微波栅控电子枪的供电系统设计,完成了从射频功率源到同轴热阴极的阻抗匹配方案,设计了一种325 MHz双模式同轴供电器件,并进行了验证与分析。     

单体烃氢同位素测试系统高温热转化装置的研制

研制了单体烃氢同位素在线测试系统(GC-TC-IRMS)中的高温热转化装置(TC).该装置主要由高温电热元件、高温裂解管、温控系统等部分组成.实验表明,高温热转化装置控温精度良好(±3 ℃);在1250～1500 ℃之间选择13个温度点,并选用最稳定的烃类化合物CH4,在每个温度点进行反复实验对比(n≥6),甲烷氢同位素值(δDCH4)随反应温度增高逐渐变轻;通过对标准多元气态烃类化合物、标准液态烃类化合物及原油样品测试结果的对比分析,表明所研制的TC具有很好的稳定性与可靠性,δDn-alkane的测试精度优于±2.5‰, 完全达到研究需求.     

ECR离子源外电子注入技术研究

使用电子枪对ECR（Electron Cyclotron Resonance）等离子体注入外电子束是继铝衬弧腔、偏压盘之后，对等离子体电子的额外补充的又一种手段，通过向弧腔中注入一定能量与流强的电子束，以期提高引出束流的流强与电荷态。但由于该方法可控参数繁多，经验积累与报道资料都很少，且设计与操作远不如偏压盘等手段简便，故一直未能得到深入研究。通过以三维仿真软件CST粒子工作室对注入到弧腔电子束的运动轨迹的模拟结果为依据、以18 GHz ECR蒸发冷却源为平台，进行了ECR等离子体注入电子束的实验，结果表明:在一定实验条件下，当注入电子束能量超过1 800 eV时，会产生一种引出的离子束流的激增现象。在这个现象中，脉冲与直流的流强均比未注入电子时要高，束流电荷态向高价方向移动，且可通过控制实验条件来控制这种现象。最后对于这种电子并未通过共振面，却能起到提高电荷态与流强的作用进行了分析与讨论，并认为该现象在改善直流束与脉冲束性能的方面都有着积极的意义。The injection of the electron beam into the ECR (Electron Cyclotron Resonance)plasma by electron gun is a new method for the additional supplementary of the plasma electron, following the aluminum chamber wall and the bias plate, we are expecting for the higher current and charge state of the ion beam with it. However, because of the controllable parameter's variety, the lack of the accumulation of experience and data, and the shortage of convenience in designing and experimental practicing compared by biased disk and other means,it has always not been intensively studied. In this article, we take the 18 GHz ECR Ion Source using evaporative cooling technique as experimental platform, do the experiment of injecting electron into ECR plasma base on the simulation result of the electron beam's path in ECR's chamber by the 3D simulation software CST the particle studio. It shows that a pulsing leap of the current of the extracting ion beam appears when the injecting electron's energy is above 1 800 eV. In the mean time, the top of the pulse and the average current of the ion beam rises, the ionization state moves to a higher level. This phenomenon can be turned on and off by controlling the experimental condition. At the last part of the article, we discuss this improvement of the current and charge state of the ion beam despite of the position's missing between the injection of electron beam and the resonance surface, and hold the opinion that this phenomenon is positive to both pulsed and direct beam.     

Experimental investigation of a pulse line ion accelerator in Lanzhou

In order to put the Pulse Line Ion Accelerator (PLIA) concept to its practical application, a small experimental platform was built. It was found that the actual axial electric field is smaller than the theoretical calculation, so the accelerated ions will enter into the deceleration zone before leaving the helix, which will seriously affect the acceleration process. Based on the improved parameters, the He⁺ with 24 keV is accelerated to 55 keV, and the proof-of-principle experiment is completed on this platform.