GaAs极化电子源激活的yo-yo过程研究

通过对GaAs晶体产生极化电子束流的实验过程研究,着重对yo-yo过程中不同的实验参数对产生极化束流以及束流稳定情况的影响进行了分析,为获得稳定而持久的极化电流提供了有力的实验支持,并讨论了极化电流强度的可控性. 关键词： GaAs晶体 极化电子束 yo-yo过程 激活     

BEPC束流极化与极化仪的研究

简要介绍了在北京正负电子对撞机（ＢＥＰＣ）上实现束流极化的必要性与可能性，以及束流极化度测量的原理与方法，还简要描述了利用一条同步辐射管道测量ＢＥＰＣ电子束流极化度的测试系统方案设计以及正在开展的实验工作。     

BEPC束流极化与极化仪的研究

简要介绍了在北京正负电子对撞机(BEPC)上实现束流极化的必要性与可能性,以及束流极化度测量的原理与方法,还简要描述了利用一条同步辐射管道测量BEPC电子束流极化度的测试系统方案设计以及正在开展的实验工作.     

95MeV/u的12C炮弹产生的二次束流强度研究

使用GANIL双消色差谱仪LISE,系统研究了95MeV/u的¹²C束流轰击铍、铜和金靶所产生的二次束流强度.实验结果和程序LISE及INTENSITY的计算结果作了比较.结果表明:对于β稳定线附近的二次束流,由程序LISE及INTENSITY计算得到的二次束流强度峰值和实验结果基本相符.但对于远离β稳定线的二次束流,计算结果高于实验值.产生二次束流的最佳靶厚相应于束流在靶子中损失大约30%的能量.铍靶产生的二次束流强度高于其余两种靶子.     

JAERI和KEK联合项目中的中能束流传输线及其升级设计

中能束流传输线(MEBT)在日本质子加速器研究设施(J-PARC)中对控制束流损失起到非常关键的作用. 中能传输线已经成功设计和建造, 并进行了束流实验. 简要介绍了中能传输线及其束流实验的结果. 为进一步减少和消除传输线中的束流切割器的上升和下降过程中产生的不稳定粒子, 以满足更高流强下的束损要求, 给出了一个带有反束流切割器的中能传输线的升级设计, 该设计已被用作该项目的备用方案. 升级设计的中能传输线要完成三个任务：完成从RFQ到DTL的束流相空间匹配; 利用束流切割器把束流切割成注入快循环时所需要的束流结构, 以及利用反束流切割器把束流切割器上升和下降时间段产生的部分偏转的不稳定粒子作用回DTL的相空间接收度内, 以减少和避免粒子丢失. 在该中能传输线中, RF偏转器被用来作为束流切割器和反束流切割器. RF偏转器是中能传输线中最关键的部件, 进一步讨论了RF偏转器作为反束流切割器的优化设计. 也给出了该传输线的动力学分析的结果.     

高能重离子超边缘碰撞中极化光致反应

本文旨在对近期高能重离子超边缘碰撞中光致产生过程的研究做一个简要综述.相对论性重离子激发的超强电磁场可以被近似认为是一束极高亮度的等效相干光子束流.本文主要讨论两类等效光子参与的高能产生过程:准实光子融合产生轻子对即Breit-Wheeler过程,以及等效光子与原子核内的胶子物质相互作用导致的矢量介子衍射产生过程.这两类过程是研究重离子超边缘碰撞的传统课题,本文主要侧重于讨论碰撞参数依赖效应与末态软光子重求和效应.另一方面,最近一系列研究揭示了相对论重离子所激发的准实光子是高度线性极化的,其极化方向平行于光子横动量方向;并指出可以通过重离子超边缘碰撞中轻子对产生过程的cos 4?方位角不对称来测量光子的线偏振度.这一理论预言随后被SATR合作组的测量所证实.伴随这一新的理论与实验进展,线性极化光子束流同时也给我们提供了一种新颖的实验手段,用来研究量子色动力学唯象学.如线偏振准实光子可导致矢量介子衍射产生过程的各种方位角不对称,通过研究这些方位角不对称可以让我们更深入地理解高能散射过程的双缝干涉效应、库仑-核反应的干涉过程,以及抽取光子维格纳函数等.本文将详述这些效应并讨论未来的理论与实...     

CSRm束流径向和轴向振荡的耦合

 介绍了由于磁铁的安装误差和螺线管的存在而造成的束流径向和轴向的耦合，以及耦合对束流稳定的影响。结合CSRm结构的典型参数分析得出：二极磁铁和四极磁铁在纵向角安装偏差为-0.5~0.5 mrad；有螺线管存在的情况下，工作点落在和共振线时，将导致束流不稳定而大量损失，落在差共振线时，束流稳定。通过模拟计算发现：螺线管产生的耦合远大于磁铁的纵向角安装偏差产生的耦合。     

CSRm束流径向和轴向振荡的耦合

介绍了由于磁铁的安装误差和螺线管的存在而造成的束流径向和轴向的耦合，以及耦合对束流稳定的影响。结合CSRm结构的典型参数分析得出:二极磁铁和四极磁铁在纵向角安装偏差为-0.5~0.5 mrad；有螺线管存在的情况下，工作点落在和共振线时，将导致束流不稳定而大量损失，落在差共振线时，束流稳定。通过模拟计算发现:螺线管产生的耦合远大于磁铁的纵向角安装偏差产生的耦合。     

强激光驱动高能极化正负电子束与偏振伽马射线的研究进展

高能自旋极化正负电子束与偏振伽马射线在高能物理、实验室天体物理与核物理等领域有十分重要的应用.近年来随着超短超强激光脉冲技术的快速发展,利用强激光与物质相互作用的非线性康普顿散射和多光子Breit-Wheeler过程为制备高极化度、高束流密度的高能极化粒子束提供了新的可能.本文对基于强激光产生高能极化正负电子束与偏振伽马射线的研究成果进行简要回顾,并介绍了这些方法的基本物理原理和主要结果.     

Al2O3:Cr荧光屏Fen+束流面分布诊断

为满足加速器束流诊断的特殊要求，对束流面分布诊断方法进行了研究，建立了一套基于荧光屏的离子束流面分布测量装置。采用Fen+(n=5~12)离子束流对测量装置进行了实验检验，结果表明，在几十至上百nA量级束流强度Fen+离子束的轰击下，面分布图像产生了饱和现象。进一步的实验结果表明，饱和现象是由荧光屏发光的光强过强造成的，采用特别研制的具有光强衰减和滤波功能的成像光路可以解决光强饱和的问题。在低束流条件下，面分布图像的灰度值与束流强度呈近似的线性关系，对这种线性关系产生的原因进行了具体的分析。     

Drive and Curiosity: What Fuels the Passion,by Istvan Hargittai

A beam of electrons may have the spins of the individual electrons preferentially polarized in a specified direction. The resulting state of polarization of the electron beam is described by a polarization vector p. This polarization vector is affected in direction and magnitude by macroscopic electric and magnetic fields. The relevance of this to precise measurement of the electronic g-factor, end to the problems of handling polarized beams (as in accelerating systems), is discussed. Some spinsensitive interactions, and various methods of producing intense highly polarized electron beams, are described. In a final paragreph an outline is given of the mathematical formalism used in describing polarization phenomene.     

Intense pulses of polarized electrons produced by Fano effect

A pulsed polarized electron source using the Fano effect on cesium is described in detail. A frequency doubled dye laser producing 2 mJ/pulse at 305 nm is used as the source of circularly polarized light. The light beam interacts with an array of 20 atomic beams. The atomic beam oven operates in a closed cycle thereby increasing running time by a factor of 30. Intensities of 3×10⁹ e ^?/0.5 μs with a polarization of 90% have been routinely obtained.     

Mono-energetic GeV electrons from ionization in a radially polarized laser beam

Fields of a radially polarized laser beam developed recently [Y. I. Salamin, Opt. Lett.31, 2619 (2006)] are employed to show that electrons produced by atomic ionization near the focus may be accelerated to GeV energies. Conditions for producing a mono-energetic and well-collimated electron beam are discussed.     

Elektronen-Spinpolarisation bei der Photoionisation unpolarisierter Cäsiumatome mit zirkularpolarisiertem Licht

Photoelectrons ejected from cesium atoms by circularly polarized light of certain wavelengths are highly spinpolarized according to Fano's theory. Measurements of the spinpolarization of photoelectrons along the wavelength spectrum are reported. The highest degree of spinpolarization obtained experimentally is 100%. Our results reveal a small deviation from the theoretically predicted spinpolarization. Apart from giving information on the influence of spin-orbit interaction on the photoionization process, the Fano-effect turns out to be a simple and efficient method for producing polarized electron beams. Though not designed as a polarized electron source, our present apparatus yields a beam of 0.3·10^?10 Ampere with a polarization of 81 ± 3% when a broad unfiltered spectral band is irradiated.     

Experimental study on the activation process of GaAs spin—polarized electron source

GaAs spin-polarized electron source is a new kind of electron source, where the GaAs semiconductor crystal is used as a photocathode under the irradiation of helicity light. In this paper the activation process of the GaAs spin-polarized electron source is unvestigated experimentally in detail, during which the negative electron affinity of the photo cathode should be achieved more carefully by absorbing the caesium and oxygen on the surface of the GaAs crystal under ultrahigh vacuum conditions. Besides the different activation processes, the important physical parameters are studied to achieve the optimum activation results. At the same time the stability and lifetime of the polarized electron beam are explored for future experiments. Some important experimental data have been acquired.     

Axially magnetized electron–positron and electron plasma competition on the self focusing of intense laser beam

The spot-size evolution of circularly polarized intense laser beam propagating through the axially magnetized electron–positron (EP) and electron plasmas is discussed, in mildly relativistic and weakly non-linear (a² ? 1) regime. The non-linear current density source terms are obtained by making used of the perturbative technique. The variational principle approach method is applied to the solution of the non-linear Schrodinger wave equation. It is shown that the laser beam spot size decreases for the left and increases for the right handed polarized beams with increasing the external magnetic field, owing to the beam passages inside the electron plasma. Furthermore, it is revealed that the self focusing property strongly enhanced in the EP plasma in comparison to the electron plasma. Moreover, self focusing of linearly polarized laser beam is investigated for EP plasma by superposition of the right and left circularly polarized beams.     

金属中逆法拉第效应的经典理论

研究电子在圆偏振光驱动下的经典动力学问题以及金属中逆法拉第效应(IFE)的经典微观机制.得到电子在圆偏振光驱动下的一个解,表明其运动轨道是螺旋线.忽略电子与磁场的相互作用,电子作绕平行于其初速度的轴、横截面为椭圆的螺旋线运动,产生了一个平行于其初速度、方向由圆偏振光的手征性决定的磁矩.磁矩的统计结果与Hertel从电子气整体出发得到的结果一致.     

Electron acceleration to GeV energy by a radially polarized laser

We present a relativistic single particle simulation of vacuum acceleration of an electron by a high-intensity radially polarized laser beam. The inherent complete symmetry of radially polarized laser beam leads to improvement in the trapping and acceleration of an electron so that an electron can be accelerated to the level of GeV. In addition, the external magnetic field further enhances the electron acceleration. Hence, an electron of ultrahigh energy was observed. The strong correlation between final electron energy and scattering angle is discussed.     

Spin-dependent hot electron transport in Co/Cu thin films

Hot-electron transport in Co/Cu/Co trilayer films has been studied in the energy range from 1.0 to 2.0 eV using ballistic electron magnetic microscopy. Both the spin-dependent attenuation lengths of Co and the cumulative polarizing effects of spin-dependent tunneling and transmission across a Co/Cu interface have been determined. For very thin (a few A) Co layers, the latter effects result in a weakly majority-spin polarized electron beam above approximately 1.3 eV and a minority-spin polarized beam below approximately 1.2 eV. For thicker Co layers the transmitted beam is always majority-spin polarized.