Intra-beam scattering studies for low emittance at BAPS

The target parameters of modern ultra-low emittance storage ring light sources are entering into a regime where intra-beam scattering (IBS) becomes important and, in the case of the Beijing Advanced Photon Source (BAPS), which is being designed at the Institute of High Energy Physics (IHEP), even a limitation for achieving the desired emittances in both transverse planes at the diffraction limit for X-ray wavelengths (≈10 pm). Due to the low emittance, the IBS effect will be very strong. Accurate calculations are needed to check if the design goal (ε_h+ε_v=20 pm) can be reached. In this paper, we present the results of numerical simulation studies of the IBS effect on a BAPS temporary design lattice.     

5-{[(4′-正戊基氧-4-联苯基基)羰基]氧}-1-戊炔的相转变与相结构

采用差示扫描量热(DSC)、一维(1D)广角X射线衍射(WAXD)、热台偏光显微镜(PLM-hotstage)等研究手段对含联苯液晶基元的侧链液晶聚炔单体5-{[(4′-正戊基氧-4-联苯基基)羰基]氧}-1-戊炔(A3EO5)的本体相转变和相结构进行了研究.DSC和1D-WAXD实验结果表明,A3EO5在升温和降温过程中均呈现四个相转变过程,形成双向性液晶.样品从各向同性态降温至室温过程中,首先形成近晶A相,随后进入层内排列具有准长程有序的近晶B相,继续降温将形成层内为正交排列的近晶E相,在此之后样品进入晶相.PLM结果指出样品在各向同性态降温过程中分别形成球状织构、角锥织构和同心圆弧织构.     

同轴线法在小孔径真空元件阻抗测量中的应用北大核心CSCD

粒子加速器中真空元件的阻抗是引起束流不稳定的重要原因。基于储存环的新一代同步辐射光源的设计发射度更小,相应地要求更小的真空盒孔径,进而带来阻抗的显著增加,这就要求在设计阶段对真空元件的阻抗进行准确的评估和优化。阻抗测量是验证阻抗模型准确性的重要手段,而同轴线法是常用的实验室测量方法。对小孔径真空元件同轴线法纵向阻抗测量进行了研究,针对窄带阻抗元件,使用pillbox腔开展了相关的阻抗测量,研究了不同的内导体尺寸对于测量结果的影响,同时基于尾场模拟、散射参数模拟以及本征模模拟对测量结果进行了验证,模拟和测量结果符合很好,并证明原有的内导体导致谐振峰频移的理论分析应用于小孔径元件时存在偏差。此外针对非窄带阻抗元件,对条带冲击磁铁结构进行了同轴线法阻抗测量,研究了内导体对结果的影响,验证了同轴线法测量的有效性。     

Realization of a locally-round beam in an ultimate storage ring using solenoids

"Ultimate" storage rings (USRs), with electron emittance smaller than 100 pm·rad and on the scale of the diffraction limit for hard X-rays in both transverse planes, have the potential to deliver photons with much higher brightness and higher transverse coherence than that projected for the rings currently operational or under construction. Worldwide efforts have been made to design and to build light sources based on USRs. How to obtain a round beam, i.e., a beam with equivalent transverse emittances, is an important topic in USR studies. In this paper, we show that a locally-round beam can be achieved by using a pair of solenoid and anti-solenoid with a circularly polarized undulator located in between. Theoretical analysis and application of this novel method, particularly to one of the Beijing Advanced Photon Source storage ring design having natural emittance of 75 pm·rad, are presented.