真空盒对二极铁场均匀性影响的研究

通过计算机模拟计算与实验相结合, 讨论了真空盒磁导率对二极磁铁磁场分布的影响. 结果表明当真空盒磁导率μ_r≠1时, 真空盒将影响磁铁磁场分布, 在磁场均匀性要求很高时, 必须考虑真空盒的材料与尺寸对磁场均匀性的影响.     

二极铁均匀场修正

HI-13串列加速器升级工程中的ISOL高质量分辨谱仪要求20000的质量分辨率, 分析磁铁磁场均匀性要求好于1×10-5。 要达到这样高的磁场均匀性, 必须对磁铁进行垫补。 介绍了二极铁表面线圈垫补均匀场的设计方法和制作工艺, 并且基于现有的一块C型二极铁对表面线圈垫补均匀场的方法进行了实验研究。 实验结果表明, 采用表面线圈垫补后, 场均匀性提高了一个数量级, 积分场的均匀性从5×10-4提高到3×10-5。 The mass resolving power of ISOL’s spectrometer for Beijing Radioactive Ion beam Facilities project is 20000, which requires the field uniformity of the magnet better than 1×10-5. To achieve such a high uniformity field,field optimize is indispensable. This paper presents the design method,manufacture techniques and experiment results of surface coils,which are set on pole face of a dipole to improve the magnetic field homogeneity. The integral field uniformity with surface coil is optimized to 3×10-5 from 5×10-4,which is improved roughly an order of magnitude.     

CR环二极磁铁的磁场优化

FAIR项目中的CR环二极磁铁对磁场积分场的误差分布要求很高,通过削斜与加载镜像板的方法是优化磁场的主要方法,文中介绍了对二极磁铁优化方法和对它的处理方法.利用削斜的方法来改变二极磁铁积分场的误差分布,通过复杂的削斜,已将其高场的误差分布优化到±2×10-4.加镜像板的方法主要适合高场,而对低场的调节不明显.另外处理方法的选取对结果的影响也很大,文中对两种方法作了比较.优化模拟计算软件采用的是专门的磁场计算工具OPERA.     

轴向二极场MWECR－CVD系统等离子体特性的实验研究

本实验设计了永磁非对称轴向二极场ＭＷＥＣＲ－ＣＶＤ系统，并对系统的等离子体特性进行了研究，获得了等离子体空间分布的图像以及气压对等离子体参数的影响。     

偶极场扰动与冷却效应对同步运动的影响

在同步加速器特别是冷却存储环中,偶极场扰动和冷却效应将会对粒子的Betatron振荡和同步振荡产生影响。 叙述了偶极场扰动对粒子同步运动的影响与高频相位调制等效, 重点研究了偶极场扰动与冷却效应同时存在的情况对粒子的同步运动产生的影响。 在经典力学框架内把粒子的同步运动方程化为广义的摆方程, 然后利用Melnikov方法对系统的稳定性进行了分析, 讨论了系统进入Smale马蹄混沌的物理意义,并导出了系统稳定的临界条件。根据稳定性判据, 给出了系统稳定性所需要的偶极场扰动的高频相位调制幅度和冷却系数的限制条件。 结果表明, 系统的稳定性与它的参数有关, 只需适当调节这些参数, 混沌便可原则上控制或避免。 The Betatron oscillation and the synchrotron oscillation for the particles are effected by the dipole field perturbation and the cooling effect. Both effects are considered in the paper and the synchrotron motion equation of the particle in the synchroton is reduced to the general pendulum equation in the classical mechanics frame. The stabilities of the system caused by dipole field perturbation and cooling are analyzed by using Melnikov method. The thresholds entered a Smale horseshoe chaos are derived in detail and the stability conditions for the system caused by dipole field perturbation and cooling are dicussed. The results show that the critical condition or the stability thresholds are related to the system parameters. The chaos or an instability can be avoided or controlled in principle by regulating some parameters of the system.     

Observation of the Dipole Blockade Effect in Detecting Rydberg Atoms by the Selective Field Ionization Method

The dipole blockade effect at laser excitation of mesoscopic ensembles of Rydberg atoms lies in the fact that the excitation of one atom to a Rydberg state blocks the excitation of other atoms due to the shift in the collective energy levels of interacting Rydberg atoms. It is used to obtain the entangled qubit states based on single neutral atoms in optical traps. In this paper, we present our experimental results on the observation of the dipole blockade for mesoscopic ensembles of 1–5 atoms when they are detected by the selective field ionization method. We have investigated the spectra of the three-photon laser excitation 5S1/2 → 5P3/2 → 6S1/2 → nP3/2 of cold Rydberg Rb atoms in a magneto-optical trap. We have found that for mesoscopic ensembles this method allows only a partial dipole blockage to be observed. This is most likely related to the presence of parasitic electric fields reducing the interaction energy of Rydberg atoms, the decrease in the probability of detecting high states, and the strong angular dependence of the interaction energy of Rydberg atoms in a single interaction volume.     

CSR二极磁铁积分磁场测量系统

介绍了兰州重离子加速器冷却储存环(HIRFL CSR)积分磁场测量系统以及积分测量的基本原理和数据处理方法,对测量结果的分析表明整个系统运行可靠稳定,可用于CSR磁铁的积分测量.This article presents the basic principle of dipole integral magnetic field measurement . The integral coil which has the same radius with the dipole magnets was used to measure the integral magnetic field of different magnets in Cooler Storage Ring(HIRFL CSR). The article also generally introduced the software and hardware systems of the automatic measurement device. According to the repetitive experiments, a suit of better measurement got to be summarized. On the other hand, the article recommends the...     

Collisionless Plasma Expansion in the Presence of a Dipole Magnetic Field

The collisionless interaction of an expanding high–energy plasma cloud with a magnetized background plasma in the presence of a dipole magnetic field is examined in the framework of a 2D3V hybrid (kinetic ions and massless fluid electrons) model. The retardation of the plasma cloud and the dynamics of the perturbed electromagnetic fields and the background plasma are studied for high Alfvén–Mach numbers using the particle–in–cellmethod. It is shown that the plasma cloud expands excluding the ambient magnetic field and the background plasma to form a diamagnetic cavity which is accompanied by the generation of a collisionless shock wave. The energy exchange between the plasma cloud and the background plasma is also studied and qualitative agreement with the analytical model suggested previously is obtained (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

CR环二极磁铁的磁场优化

FAIR项目中的CR环二极磁铁对磁场积分场的误差分布要求很高, 通过削斜与加载镜像板的方法是优化磁场的主要方法, 文中介绍了对二极磁铁优化方法和对它的处理方法. 利用削斜的方法来改变二极磁铁积分场的误差分布, 通过复杂的削斜, 已将其高场的误差分布优化到±2×10^－4. 加镜像板的方法主要适合高场, 而对低场的调节不明显. 另外处理方法的选取对结果的影响也很大, 文中对两种方法作了比较. 优化模拟计算软件采用的是专门的磁场计算工具OPERA.     

四杆与四翼型RFQ内的二极场研究

RFQ (射频四极透镜) 是直线加速器中最重要的前级聚焦加速结构,其工作模式下束流孔中的电场四极对称性是保证束流品质及加速效率的关键。为了解决其各自存在的工作模式下四极场的不对称问题,分别对四杆型RFQ 和四翼型RFQ 的结构和模式谐振特性做了研究。针对四翼型RFQ,模拟显示双端口对称耦合的方式从抵消二极模式和提高结构对称性两方面来达到削弱工作模式下的场分布中二极量的目的,对一个1 m段四翼RFQ 模型腔的测量证实了双端口对称耦合抵消腔内二极模式的有效性;针对四杆型RFQ 的二极场,以SSC-Linac 项目的RFQ 为原型,利用三维模拟计算软件CST-MWS 进行模拟,通过改进支撑板的结构并调整参数,完全地消除了工作模式下的极间二极场,且理论上此种改进方法对支撑板结构的四杆型RFQ 均有效。Radio Frequency Quadruple(RFQ) is the most important front-end acceleration structure in linear accelerators.It can focus and accelerate beam in longitudinal and transversal direction, simultaneously. Symmetric of electric field in acceleration aperture is very important for the beam dynamics. To an idea RFQ, there is only quadruple electric field in the acceleration aperture. The dipole field in aperture is harmful and need be as small as possible. The methods to reduce it are studied in a four-rod RFQ and a four-vane RFQ in the article ndependently. To a four-vane RFQ, the symmetrical double-port couplers are employed to counteract the neighboring dipole modes. The availability is confirmed by the simulation with the 3-D Finite Element tool, CST-MWS. And it is also observed by measuring a model-cavity with a symmetrical double-port couplers. To a four-rod RFQ, a new structure of stems is proposed to reduce the dipole mode.Taking the RFQ for the SSC-LINAC project as example, the dipole mode contributions to the electric filed is completely eliminated by selecting stem’s parameters carefully. It is confirmed by the simulation of CST-MWS. heoretically, this method is independent with the frequency of an RFQ and serves for all RFQs with 4-rod or 4-wane structure.