EicC对撞光学设计

EicC是中国科学院近代物理研究所计划建造的中国电子-离子对撞机装置,该对撞机质心能位于20 GeV附近,是研究海夸克的最佳能量窗口,同时还可研究胶子和价夸克。EicC对撞粒子为高极化率质子和电子束团,质子环pRing采用八字环设计方案,可以更好地保持极化质子束团极化率,电子环eRing采用跑道形环设计方案,可以更好地利用隧道空间。该装置电子束流能量中心值为3.5 GeV,电子束RMS发射度为水平方向60 nm·rad,垂直方向60 nm·rad,对撞点b函数为水平方向0.4 m,垂直方向0.12 m;质子束流能量中心值20 GeV,质子束RMS发射度为水平方向300 nm·rad,垂直方向180 nm·rad,对撞点b函数为水平方向0.08 m,垂直方向0.04 m,设计亮度2×1033 cm–2s–1。EicC采用双对撞区非对称光学设计,通过对EicC不同色品补偿方案的研究,最终确定了弧区加短直线节共同补偿的色品补偿方案;通过研究对撞点处b函数以及对撞点间相移对动力学孔径的影响,最终得到pRing动力学孔径大于8 s(s为束团RMS尺寸)、eRing动力学孔径大于20 s,满足大于束团尺寸6 s的要求。     

双平面多圈注入模拟优化程序TPIS的初步开发与验证

为满足短时间内达到高累积流强要求,HIAF/BRing采用了一种新的注入方法--双平面相空间多圈注入。该注入方法与传统单平面多圈注入方法不同,而且在国际上是首次在实际项目中采用,尚无实际运行经验。因此,对注入过程进行程序模拟研究是验证双平面多圈注入方案可行性的必要手段。为详细模拟研究BRing双平面多圈注入过程,并克服已有程序跟踪速度较慢且注入参数修改不便的缺点,本文根据双平面多圈注入的特点,建立了双平面多圈注入模型,编写了双平面多圈注入模拟优化程序TPIS（Two-Planemultiturn Injection Simulation）。通过与ORBIT程序模拟结果对比,验证了TPIS程序模拟双平面多圈注入过程的正确性。在此基础上,在TPIS程序中加入了粒子群优化算法,并对BRing注入参数进行了优化。结果表明,TPIS程序可以对注入参数进行有效优化,经过优化后,束流损失减少了28%,最终剩余累积粒子数满足BRing的流强设计指标要求,进一步验证了双平面多圈注入设计的可行性。     

HIAF-BRing束团合并过程中的束流负载效应模拟

强流重离子加速器HIAF-BRing在加速完成后进行束团合并，为研究BRing中的束流负载效应对束团合并的影响，对238U35+束流进行了粒子跟踪模拟。模拟结果显示，在束团合并过程中，束流负载效应引起束团长度和束团中心位置的振荡，导致束流动量分散和束团长度的增长。束团合并过程中尾场电压以及不同束团间尾场的耦合导致的势阱畸变，是引起束团长度和束团中心振荡及束流发射度增长的原因。为了降低束流负载效应的影响，采用多谐波前馈系统进行补偿，达到了补偿束团合并过程中的束流负载效应的目的，从而确保了BRing中引出束流的品质，同时根据模拟结果确定了前馈系统需要覆盖的频率范围和需要补偿的最大尾场电压。     

IH型漂移管直线加速器的束流动力学研究（英文）

为了提高兰州重离子加速器冷却储存环（HIRFL-CSR）的运行效率、改善加速器输出束流品质,并实现几个加速装置分时供束,提高整个重离子加速装置的利用率,特为（HIRFL-CSR）增建一台新的注入器--CSRLINAC。在108.48 MHz的RFQ之后的CSR-LINAC主加速段,主要由一台108.48 MHz和两台216.96 MHz的IH型漂移管直线加速器组成,用于加速荷质比为1/8.5~1/3之间的重离子,其最大的束流流强为3 mA,并将粒子从0.3 MeV/u加速到3.71 MeV/u。运用KONUS动力学原理,在满足设计指标的情况下,首先利用TraceWin程序进行中能束线MEBT设计,后针对高频腔体设计和束流匹配的基本参数的系列讨论,特别是对CSR-LINAC的中能束流匹配线、参数选择和IH型KONUS结构的漂移管直线加速器进行设计模拟优化。最终得出,在保证腔体设计指标和95.3%的传输效率的情况下,该紧凑型直线加速结构经过三个腔体的加速后,束流的纵向归一化均方根发射度增长仅有25%;同时发现,当流强达到3 mA时,存在空间电荷效应,导致其纵向相宽增长约25%,最大横向包络也存在16.5%的涨落。In order to improve the operation efficiency of the Cooling Storage Ring of Heavy Ion Research Facility in Lanzhou (HIRFL-CSR), a heavy ion linac (linear accelerator) was proposed and designed as a new injector for HIRFL-CSR. Following the 108.48 MHz Radio-Frequency Quadrupole (RFQ), three tanks in total with Interdigital H-mode drift tube linac (IH-DTL) structure are installed to boost the beam energy from 0.3 to 3.71 MeV/u, and the beam current of ions with charge-to-mass ratio from 1/8.5 to 1/3 can reach to 3 mA. The first tank operatesat the same frequency as the RFQ, and the rest two operate at 216.96 MHz. The “Combined Zero-Degree Synchronous Particle Structure” (KONUS) beam dynamics was used in the beam dynamics design. The overview of the physics design on the main accelerating components, including RF design and beam dynamics design are introduced in this paper. The optimized structure design, fabrication status and simulation results are presented in this contribution. It shows that under the condition of assurance of 95.3% transmission efficiency, the normalized rms emittance is about 25%. When the beam current is up to 3 mA, owing to the space charge effect, the increase of longitudinal phase spread and transverse envelope are about 25% and 16.3%, respectively.     

BRing中电荷交换引起的束流损失分布模拟计算

在强流重离子加速器运行中,带电粒子与真空管道中的残余气体分子相互作用发生的电荷交换反应是影响重离子束流寿命的关键因素。这种电荷交换过程导致的束流损失将解吸出真空管壁上吸附的气体分子,进而引起真空压力的动态变化,将严重影响加速器的稳定运行和最终束流引出流强。中国科学院近代物理研究所将在广东省惠州市建造的强流重离子加速器装置（High Intensity heavy-ion AcceleratorFacility,简称HIAF）利用增强器（Booster Ring,简称BRing）提供束流流强高达2×1011 ppp的238U35+用于核物理及原子物理等实验研究。对强流重离子加速器BRing中238U35+束流发生电荷交换反应,损失一个电子成为238U36+的过程进行了追踪模拟,计算得到了U36+损失前的运动径迹和全环粒子损失位置分布,模拟结果显示U36+受到色散元件的影响,将集中损失在位于二极磁铁后的漂移节区域中。基于模拟结果,在束流损失位置处设计安装由低解吸率材料制作的准直器,优化设计后的准直效率高达95%以上;并模拟计算了有无准直器时真空压力和束流流强的变化,安装准直器后BRing的平均真空度变化小于10%,将确保BRing加速器的稳定运行。During heavy ion accelerator operation, the charge exchange effect between ions and residual gas molecules is the key factor to influence beam lifetime. The charge exchange process has ions lost on the wall and leads to a dynamical vacuum change, which will seriously affect the accelerator operation and reduce the extraction beam intensity. The Institute of Modern Physics' future project, called High Intensity heavy ion Accelerator Facility (HIAF), will be built in Huizhou city, Guangdong Province, China. The Booster Ring (BRing) will provide 2×11 ppp 238U35+ for nuclear physics experiments. This article studies the track of particle U36+ before impacting on the wall, which is the reference particle U35+ losing one electron, and gets the U36+ loss distribution along the BRing. The simulation result shows that U36+ will be influenced seriously by dispersion elements, and will be lost in the drift sections after the dipoles. Collimators made out of materials with low desorption will be installed in the particles lost positions. The collimator efficiency after optimization can be larger than 95%. It also shows BRing average pressure change and beam intensity change between collimators on and off. The result points out that the BRing average pressure change will be less than 10% with collimators on, which makes BRing operate stably.     

Effect of In_x Ga_(1-x )N “continuously graded” buffer layer on InGaN epilayer grown by metalorganic chemical vapor deposition

In this paper we report on the effect of an In x Ga1-x N continuously graded buffer layer on an InGaN epilayer grown on a GaN template.In our experiment,three types of buffer layers including constant composition,continuously graded composition,and the combination of constant and continuously graded composition are used.Surface morphologies,crystalline quality,indium incorporations,and relaxation degrees of InGaN epilayers with different buffer layers are investigated.It is found that the In x Ga1-x N continuously graded buffer layer is effective to improve the surface morphology,crystalline quality,and the indium incorporation of the InGaN epilayer.These superior characteristics of the continuously graded buffer layer can be attributed to the sufficient strain release and the reduction of dislocations.     

Effect of InxGal-xN ＂continuously graded＂ buffer layer on InGaN epilayer grown by metalorganic chemical vapor deposition

In this paper we report on the effect of an lnxGal xN continuously graded buffer layer on an InGaN epilayer grown on a GaN template. In our experiment, three types of buffer layers including constant composition, continuously graded composition, and the combination of constant and continuously graded composition are used. Surface morphologies, crystalline quality, indium incorporations, and relaxation degrees of InGaN epilayers with different buffer layers are investigated. It is found that the InxGa1-xN continuously graded buffer layer is effective to improve the surface morphology, crystalline quality, and the indium incorporation of the InGaN epilayer. These superior characteristics of the continuously graded buffer layer can be attributed to the sufficient strain release and the reduction of dislocations.     

化学实验教学中的测量不确定度

在化学实验教学实践中由于误差分析的角度和方法不同,显著影响了实验数据和结果的表达和比较.实验结果和误差分析采用测量不确定度表达方式,可克服传统误差理论的弊端,有效提高实验数据分析效率.通过介绍大学化学实验教学中测量不确定度的由来、意义和评定要领,完成一个评定实例,以期扩展测量不确定度评定方法在化学实验教学中的应用范围,推动新知识在化学实验教学中的普及.     

Peptide backbone-copper ring structure: A molecular insight into copper-induced amyloid toxicity

Copper ions can promote amyloid diseases that are associated with amyloid peptides, such as type 2 diabetes (T2D), Alzheimer's disease (AD), Parkinson's disease (PD), and amyotrophic lateral sclerosis (ALS). However, the underlying molecular mechanism remains obscure. Here we present that Cu²⁺ is able to specifically bind to the backbone of T2D-related human islet amyloid polypeptide (hIAPP) by forming a ring structure, which causes the reduction of Cu²⁺ to Cu⁺ to produce reactive oxygen species (ROS) and the modulation of hIAPP aggregation. Nuclear magnetic resonance spectroscopy showed that Cu²⁺ bound to the backbone of a turn region, His18—Ser21, which is critical for hIAPP aggregation. Ab initio calculations and x-ray absorption fine structure analyses revealed that Cu²⁺ simultaneously bound with both the amide nitrogen and carbonyl oxygen on the peptide backbone, resulting in a ring structure, and causing the reduction of Cu²⁺ to Cu⁺ to form a hIAPP-Cu⁺ complex. 2',7'-dichlorodihydrofluorescin diacetate fluorescence measurements further indicated that this complex led to enhanced ROS levels in rat insulinoma cells. Additionally, thioflavin T fluorescence and atomic force microscopy measurements denoted that the backbone-Cu ring structure largely modulated hIAPP aggregation, including the inhibition of hIAPP fibrillation and the promotion of peptide oligomerization. These findings shed new light on the molecular mechanism of Cu²⁺-induced amyloid toxicity involving both the enhancement of ROS and the modulation of hIAPP aggregation.     

Influence of Si doping on the structural and optical properties of InGaN epilayers

Influences of the Si doping on the structural and optical properties of the InGaN epilayers are investigated in detail by means of high-resolution X-ray diffraction （HRXRD）, photolumimescence （PL）, scanning electron microscope （SEM）, and atomic force microscopy （AFM）. It is found that the Si doping may improve the surface morphology and crystal quality of the InGaN film and meanwhile it can also enhance the emission efficiency by increasing the electron concentration in the InGaN and suppressing tile formation of V-defects, which act as nonradiative recombination centers in the InGaN, and it is proposed that the former plays a more important role in enhancing the emission efficiency in the InGaN.