超二代微光像增强器Na2KSb(Cs)多碱光电阴极荧光谱研究

利用785 nm波长激光作为激发源,测量了超二代微光像增强器Na2 KSb (Cs)多碱光电阴极的荧光谱.试验中发现该荧光谱不是一条光滑的高斯型曲线,而是一条在高斯型荧光谱上叠加了一定频率间隔小锯齿峰的曲线.经实验验证和理论分析证明该荧光谱上的小锯齿峰是一种干涉条纹,与超二代微光像增强器的结构有关.干涉条纹之间的间距与...     

Study of the THGEM detector with a reflective CsI photocathode

The THGEM detector without and with a CsI has been tested successfully. The optimal parame- ters of THGEM have been determined from eight samples. The UV photoelectric effect of the CsI photocathode is observed. The changing tendency related to the extraction efficiency (ε<,extr>) versus the extraction electric field is measured, and several electric fields influencing the anode current are adjusted to adapt to the THGEM detector with a reflective CsI photocathode.     

Bunch length measurement at Tsinghua Thomson scattering X-ray source

The length of electron beam from a photocathode RF gun is determined by a spectrometer, according to the relative energy spread induced by the bunch length during the acceleration in a linac. For a photocathode RF gun, different laser injected phase and beam charge are studied. The compression is changed for the different laser phases, as from 10° to 30°, and the bunch length is lengthened due to the strong longitudinal space charge force, caused by the increased charge.     

反射式负电子亲和势GaN光电阴极的光电发射及稳定性研究

利用在线多信息紫外光电阴极激活评估系统,测试了真空室内两个GaN 光电阴极Cs,O激活后及衰减6 h和18 h后补Cs的光谱响应特性曲线和量子效率曲线;并绘制了光纤光源波长为300 nm的光电阴极响应电流衰减变化曲线.实验结果证明,GaN 光电阴极较GaAs阴极具有更好的稳定性,量子效率可保持相对稳定达10 h,然后缓慢衰减,衰减速率较窄禁带半导体材料低得多.补Cs后光电流最大值较刚激活完有16.8%的增长,这充分证明阴极表面量子效率衰减的原因是Cs的脱附,而不是O的吸附.这些现象可由双偶极层模型来解释, 关键词： 光学 光电阴极 量子效率 稳定性     

GaAs光电阴极激活时Cs的吸附效率研究

从NEA GaAs光电阴极的激活光电流曲线发现,当系统真空度不很高时,在首次Cs激活阶段,表面掺杂浓度较低的阴极材料,其光电流产生需要的时间也较长.同时,随着系统真空度的提高,这种时间上的差异又变得不再明显.该现象表明,Cs原子在阴极表面的吸附效率同表面层掺杂浓度以及系统真空度之间有直接的联系.为定量分析这种关系,本文根据实验数据建立了Cs在阴极表面吸附效率的数学模型,利用该模型仿真的结果同实验现象非常符合.该研究对进一步开展变掺杂阴极结构设计和制备工艺研究具有重要的价值和意义. 关键词： GaAs光电阴极 吸附效率 真空度 表面掺杂浓度     

Study of the THGEM detector with a reflective CsI photocathode

The THGEM detector without and with a CsI has been tested successfully. The optimal parameters of THGEM have been determined from eight samples. The UV photoelectric effect of the CsI photocathode is observed. The changing tendency related to the extraction efficiency (ε_extr) versus the extraction electric field is measured, and several electric fields influencing the anode current are adjusted to adapt to the THGEM detector with a reflective CsI photocathode.     

Self-adjointness of unbounded tridiagonal operators and spectra of their finite truncations

This paper addresses two different but related questions regarding an unbounded symmetric tridiagonal operator: its self-adjointness and the approximation of its spectrum by the eigenvalues of its finite truncations. The sufficient conditions given in both cases improve and generalize previously known results. It turns out that, not only self-adjointness helps to study limit points of eigenvalues of truncated operators, but the analysis of such limit points is a key help to prove self-adjointness. Several examples show the advantages of these new results compared with previous ones. Besides, an application to the theory of continued fractions is pointed out.     

序半群的阿基米德半群的半格分解

本文通过一个序半群S上的一些二元关系以及它的理想的根集的性质该序半群是阿基米德半群的半格,特别地是阿基米德半群的链的刻划,证明了S是阿基米德链当且仅当S是准素的.通过序半群的m-系的概念,证明了S的任意半素理想是含它的所有素理想的交,并通过该结论,证明了S是阿基米德半群的链当且仅当S是阿基米德半群的半格且S的所有素理想关于集包含关系构成链.作为应用,该结论在一般的半群（没有序）[1]中也成立.     

Emittance measurement & optimization for the photocathode RF gun with laser profile shaping

The Laser Undulator Compact X-ray source(LUCX) is a test bench for a compact high brightness X-ray generator,based on inverse Compton Scattering at KEK,which requires high intensity multi-bunch trains with low transverse emittance.A photocathode RF gun with emittance compensation solenoid is used as an electron source.Much endeavor has been made to increase the beam intensity in the multi-bunch trains.The cavity of the RF gun is tuned into an unbalanced field in order to reduce space charge effects,so that the field gradient on the cathode surface is relatively higher when the forward RF power into gun cavity is not high enough.A laser profile shaper is employed to convert the driving laser profile from Gaussian into uniform.In this research we seek to find the optimized operational conditions for the decrease of the transverse emittance.With the uniform driving laser and the unbalanced RF gun,the RMS transverse emittance of a 1 nC bunch has been improved effectively from 5.46 πmm.mrad to 3.66 πmm.mrad.     

北京大学高平均流强光阴极电子枪驱动激光系统

DC-SC超导光阴极注入器将直流光阴极电子枪和超导加速腔结合在一起,其特点之一是适合于提供高平均流强电子束.文中介绍了直流光阴极电子枪的驱动激光系统的研制.该驱动激光系统的主机为瑞士TBP公司的GE-100-XHP型激光器,是采用可饱和吸收镜技术的被动锁模激光器,其工作晶体为Nd:YVO₄,输出波长为1064nm,脉冲重复频率为81.25MHz,平均功率10W.该驱动激光系统配套的CLX-1100同步控制器可以将激光脉冲与射频参考信号严格锁定,随机抖动不大于1ps.根据使用要求,作者研制了高效的激光倍频器,获得了大于1W的266nm紫外激光.同时,激光到光阴极的传输设计中,采用了傅立叶光学技术,在紫外激光功率650mW左右的条件下,从自行研制的Cs₂Te光阴极上实现了大于500μA的光电流引出