北京自由电子激光Wiggler中电子轨迹偏离的改进

提出了一种从实验上确定用于北京自由电子激光(BFEL)装置的Wiggler中NdFeB矩形磁块的轨迹敏感系数β的方法.用β值来表征磁单块在Wiggler中对电子轨迹的贡献,并用此β值对磁块进行挑选,优化组合,可达到改进Wiggler对电子轨迹偏离的目的.     

摆动器场误差对自由电子激光器自发辐射谱的影响

在考虑平面型摆动器（Ｗｉｇｇｌｅｒ）场误差△Ｂ（ｚ）的情况下，求解电子在磁场中运动的洛仑兹（Ｌｏｔｅｎｔｚ）方程，得到场误差对电子横向速度的改变，然后作傅里叶变换即为电子自发辐射谱的改变，并讨论了各种场误差对自由电子激光器自发辐射谱的影响，选择北京自由电子激光器（ＢＦＥＬ）参数，进行模拟，最后确定出各种场误差的可接受条件。     

YBCO超导块的磁浮力及其测量

磁浮力Ｆ是块状ＹＢＣＯ超导体重要的实用参数之一,其数值大小不仅依赖材料自身的性质,而且与测量条件有关．实验结果表明,磁浮力随单畴超导块直径的增加而增大,且明显地受测试用永久磁铁表磁强度Ｂｓ及其分布的影响,最大磁浮力Ｆ０与Ｂ２ｓ成比例．观察到磁浮力随致冷剂温度的升高而降低,随时间对数衰减．另外,磁浮力的测量值还和超导块与永久磁铁的尺寸搭配有关．     

有机超导体κ-(BEDT-TTF)_2Cu(SCN)_2单晶的SHUBNIKOV-DE HAAS效应

测量了有机超导体κ（ＢＥＤＴＴＴＦ）２Ｃｕ（ＳＣＮ）２单晶的Ｘ射线衍射和强磁场下磁阻．样品沿垂直于传导面的晶格常数为１．４９ｎｍ．在１．２Ｋ温度，磁场垂直于传导面的位形下，在６Ｔ以上观测到磁阻振荡，即ＳｈｕｂｎｉｋｏｖｄｅＨａｓ效应．由ＦＦＴ（ＦａｓｔＦｏｕｉｅｒＴｒａｎｓｆｏｒｍａｔｉｏｎ）谱图，我们发现了对应于κ（ＢＥＤＴＴＴＦ）２Ｃｕ（ＳＣＮ）２单晶Ｆｅｒｍｉ面闭合轨道Ｆα频率和开放轨道磁突破频率Ｆβ的存在，Ｆα＝６２０±３０Ｔ，Ｆβ＝４１００±２００Ｔ．     

混合型波荡器的研制

介绍一台１．５ｍ的混合型波荡器（ＵＮＤＵＬＡＴＯＲ）的研制，包括设计、磁块的优化组合、磁场测量系统和磁场调整技术。这台波荡器主要用于中红外自由电子激光的研究，其磁场峰值均方根误差０．５％，磁场导向误差１ｍＴ·ｃｍ，电子轨迹偏离０．０３ｍｍ。     

平行下垂直磁化下多层磁膜巨磁电阻与外磁场关系的唯象理论计算

用Ｃａｍｌｅｙ和Ｂａｒｎａｓ等人的唯象理论方法，计算了相邻铁层间具有反铁磁耦合的的层数较多的Ｆｅ／Ｃｒ多层膜，在外磁场平行和垂直于膜面情况下的磁电阻与外磁场的关系，并与实验结果作了比较，符合得较好。在计算中利用对称性条件，对Ｃａｍｌｅｙ和Ｂａｒｎａｓ等人的理论进行了简化，求出了电子分布函数和磁电阻的显式解。     

平行与垂直磁化下多层磁膜巨磁电阻与外磁场关系的唯象理论计算

用Ｃａｍｌｅｙ和Ｂａｒｎａｓ等人的唯象理论方法，计算了相邻铁层间具有反铁磁耦合的层数较多的Ｆｅ／Ｃｒ多层膜，在外磁场平行和垂直于膜面情况下的磁电阻与外磁场的关系，并与实验结果作了比较，符合得较好。在计算中利用对称性条件，对Ｃａｍｌｅｙ和Ｂａｒｎａｓ等人的理论进行了简化，求出了电子分布函数和磁电阻的显式解。     

磁约束环境下气体激光介质中电子能量分布与电子输运系数的理论研究

引进磁作用的Ｂｏｌｔｚｍａｎｎ输运方程应用于一类特殊激励的激光器─—工作在横向磁场下的直流放电气体激光器中的工作介质．以二氧化碳激光器为研究对象，通过数值求解Ｂｏｌｔｚｍａｎｎ方程，研究了磁场对电子能量分布及电子输运系数的影响．通过分析，提出了以磁约束作用提高一般气体激光器效率的设想． 关键词：     

非晶合金Fe_(78)Si_9B_(13)在脉冲电流作用下的单相晶化

对非晶合金Ｆｅ７８Ｓｉ９Ｂ１３进行了超短脉冲电流处理，实现了晶化时αＦｅ（Ｓｉ）单相结构析出．可以认为，脉冲电流作用时，电子运动与非晶中空位型结构缺陷间的周期性排斥效应促进了类金属原子从非晶结构单元中析出，使Ｆｅ（Ｓｉ）原子局部富集，导致基体金属相在较低温度下优先成核．而在空位的定向迁移的同时，将伴随Ｂ原子的扩散，则Ｂ原子局域富集，ＦｅＢ化合物的形核析出就要受到这两个因素的抑制     

有奖征答

有奖征答１．Ａ、Ｂ、Ｃ三个质量相同的木块，已知它们的质量ｍ＝２ｋｇ，墙壁光滑木块不光滑，现被一个与竖直方向成θ＝３７°角的力Ｆ压在墙上而静止．求；（１）Ｂ对Ａ及Ｃ对Ｂ的摩擦力？（２）Ｆ＝？２．如图，Ａ、Ｂ为二质量相同的小球，Ａ用轻绳系住悬挂于Ｏ点，Ｂ...     

大功率电子加速器光学性能的研究

利用在SC程序基础上的改进程序对一种工业用大功率电子加速器的光学系统性能进行了研究.经过优化计算并给出了计算结果.     

CSR实验环电子冷却装置的纵向电子束温度

电子冷却装置中, 电子束纵向温度是计算冷却力的主要参量之一. 当电子与被冷却离子的相对速度很小时, 纵向冷却力与离子速度呈线性关系, 并且线性区域的宽度与电子束纵向温度有关. 通过分析影响电子束纵向温度的主要因素, 得到了兰州重离子冷却储存环实验环(CSRe)电子冷却装置中电子束纵向温度的大小.     

Electron diffraction

T. B. Rymer Methuen, London; Barnes and Noble, New York, 165 pages, 7 plates. £2.50     

电子冷却

本文概述电子冷却原理及其国际现状.This paper briefly describes the principle of electron cooling and the current status.     

Compact Electron Gun for High-Voltage Electron Cooling Systems

Physics of Particles and Nuclei Letters - One way to increase the efficiency of electron cooling is to increase the electron density in the beam reference frame. As a rule, with an increase in the...     

Electron crystallization

The arguments leading to the concept of an electron crystal in the low density regime of ‘jellium’ are reviewed. Ground-state properties discussed include estimates of the critical density at which the transition to a crystalline state takes place, and then in the low density regime the dielectric function, pair function and momentum distribution are dealt with. The magnetic character of the ground state as a function of density is also considered.

The low-lying excitations of the Wigner electron crystal are phonon-like and hence the low temperature specific heat obeys a T ³ law. Defect models are considered in order to throw further light on the character of excited states.

Finally experimental conditions favourable for electron crystallization are briefly considered.     

Electron Conductance and Lifetimes in a Ballistic Electron Waveguide

Ballistic electron waveguides are open quantum systems that can be formed at very low temperatures at a GaAs/AlGaAs interface. Dissipation due to electron–phonon and electron–electron interactions in these systems is negligible. Although the electrons only interact with the walls of the waveguide, they can have a complicated spectrum including both positive energy bound states and quasibound states which appear as complex energy poles of the scattering S-matrix or energy Green's function. The quasibound states can give rise to zeros in the waveguide conductance as the energy of the electrons is varied. The width of the conduction zeros is determined by the lifetimes of the quasibound states. The complex energy spectrum associated with the quasibound states also governs the survival probability of electrons placed in the waveguide cavities.     

Practical Aspects of Copper Ion-Based Double Electron Electron Resonance Distance Measurements

We present experimental conditions that lead to high-quality Cu²⁺-based double electron electron resonance (DEER) data. Such experiments are feasible at temperature of about 20 K, and sample concentrations in the range of 0.15–1.5 mM. By systematically investigating the effects of pulse lengths, we find that observer π pulse lengths of 20–48 ns provide reasonable modulation depths as well as signals. The length of the pump pulse needs to be minimized (16 ns in our case). For a Cu²⁺–Cu²⁺ DEER measurement, the optimal frequency offset is about 100 MHz. For a Cu²⁺–nitroxide DEER measurement, the frequency offset is often varied in the range of 100–500 MHz, to probe orientational selectivity. For both cases, the frequency of the pump pulse should be smaller than the observer pulse in order to obtain a larger modulation depth.     

200kV电子帘加速器的电子束轨迹的计算

采用法国的MAFIA程序计算电场.编制了TRAJ程序,用逐点跟踪计算电子轨迹,得到了束流包络.观察了在高压电场中栅压对束流光学传输的影响,并获得了在不同能量范围内的栅压聚焦作用,为栅压调节提供了理论依据,也为将来对其它规格的电子帘加速器的物理设计积累了十分宝贵的经验.