Study of radiation background at the north crossing point of the BEPCⅡ in collision mode

Understanding the radiation background at the north crossing point (NCP) in the tunnel of BEPCII is crucial for the performance safety of the High Purity Germanium (HPGe) detector, and in turn of great significance for long-term stable running of the energy measurement system. Therefore, as the first step, a NaI(Tl) detector is constructed to continuously measure the radiation level of photons as background for future experiments. Furthermore, gamma and neutron dosimeters are utilized to explore the radiation distribution in the vicinity of the NCP where the HPGe detector will be located. Synthesizing all obtained information, the shielding for neutron irradiation is studied based on model-dependent theoretical analysis.     

北京自由电子激光最近进展──实现饱和振荡

北京自由电子激光(BFEL)装置于1993年底在10.68μm处实现了饱和振荡.输出激光能量为3mJ,饱和平顶宽度2μs.对应饱和振荡平均功率为210kW(宏脉冲),峰值功率约为20MW,比自发辐射高8个量级,单程小讯号净增益为24%,转换效率为0.45%,与理论预期结果相符.光束质量接近衍射极限.目前装置可工作于9-11μm.     

用电光采样法测量相对论电子束团长度

 介绍了电光采样法测量电子束束团长度的实验原理和装置,理论分析并模拟计算了被测电子束团库仑场分布、ZnTe晶体的电光效应与束团电场的关系,并利用琼斯矩阵法分析了探测光通过电光晶体时在束团电场作用下的偏振变化、测量信号与束团长度的关系等。分析表明：测量中应使束团库仑场垂直于ZnTe的［001］方向,探测光偏振方向与ZnTe晶体y″轴成45°或者135°夹角,1/4波片快轴与探测光偏振方向夹角应取45°,这时平衡探测器输出信号与束团库仑场Eb成正比。1/4波片的作用是将电光晶体的工作点从非线性段移到线性段,平衡探测的作用是简化信号与Eb的关系,并提高信噪比。为实际测量应用提供参考。     

利用脉冲负反馈压缩准分子激光脉冲

分析了准分子激光脉冲在放大过程中的展宽现象。将饱和开关技术应用于放电泵浦激光器放大腔的放大压缩,发展了脉冲负反馈饱和压缩技术。利用该技术在天光一号系统前端LPX-150激光器上成功获得能量100 mJ、脉宽10 ns的脉冲输出,其空间分布均匀性保持在3%以内。这证明该技术可与无阶梯诱导非相干技术联合使用,在保证光束均匀性基础上进行脉冲压缩。     

BXERL photo-injector based on a 217 MHz normal conducting RF gun

The Beijing X-ray Energy Recovery Linac (BXERL) test facility is proposed in Institute of High Physics (IHEP). In this proposal, the main linac requires the injector to provide an electron beam with 5 MeV energy and 10 mA average current. An injector based on DC gun technology is the first candidate electron source for BXERL. However, the field emission in the DC gun cavity makes it much more difficult to increase the high voltage to more than 500 kV. Another technology based on a 217 MHz normal conducting RF gun is proposed as the backup injector for this test facility. We have designed this RF gun with 2D SUPERFISH code and 3D MICROWAVE STUDIO code. In this paper, we present the optimized design of the gun cavity, the gun RF parameters and the set-up of the whole injector system. The detailed beam dynamics have been done and the simulation results show that the injector can generate electron bunches with RMS normalized emittance 1.0 uppi mmcdotmrad, bunch length 0.77 mm, beam energy 5.0 MeV and energy spread 0.60%.     

Beam energy measurement system at BEPCⅡ

The beam energy measurement system at BEPCII is composed of there parts： laser source and optics system, laser-electron interaction system and High Purity Germanium （HPGe） detector system. The special components and construction of each part are introduced, especially about radiation background measurement in the storage ring, which is of great importance for the safe commissioning of HPGe detector.     

电光采样(EOS)法测量超短电子束束团长度中的模拟计算与误差分析

随着高能物理的发?高能量正负电子对撞机,射线自由电子激光器,先进的同步光源等,都需要产生高流强超短脉冲的相对论电子束团.于是,亚皮秒电子束束团诊断成为加速器物理新发展的关键技术,电子束长度的监测是其中的一部分.电光采样(EOS)法测量超短电子束团长度有非侵入、非破坏、实时测量的特点,具有较好的应用前景.本文介绍该方法的原理,通过模拟计算分析电子束束团与探测光间距、电子束电场与电光晶体晶轴夹角、探测光偏振方向与电光晶体晶轴夹角等实验参数与束团长度测量的关系,做系统误差分析,对实际实验有指导意义.     

用于光阴极的光纤激光研制实验

为获得高亮度低发射度的电子束,研制高重复频率高平均功率的光阴极驱动激光系统非常关键。利用光纤激光技术,设计了100 MHz和1.3GHz的激光系统。激光系统为全光纤结构,采用了掺镱光子晶体光纤作为放大器增益介质。在初步验证实验中,红外激光输出27 W,倍频后绿光达到6 W。     

强流目标的DC-SRF-II光阴极驱动激光系统设计

为推动北京大学超导加速器实验装置不断向强流目标迈进,提出100 W红外高重频光阴极驱动激光的设计方案,主放大器采用先进的光子晶体增益光纤,保证输出光束的质量。对激光系统中的关键问题,如各部分功率指标、脉冲展宽和压缩、激光耦合等进行了设计,并且考虑了激光的非线性影响。为实现强流加速器开机运行所必备的诊断模式,也提出了对于高重频激光进行两级选频的独特设计方案。将高速的SOA光开关和低速的声光调制器相结合,产生宏脉冲结构的输出激光,从而实现加速器在诊断模式下的运行。     

Measurement of radiation dose at the north interaction point of BEPCⅡ

The technique details for measuring radiation dose are expounded. The results of gamma and neutron radiation levels are presented and the corresponding radiation shielding is discussed based on the simplified estimation. In addition, the photon radiation level move as background for future experiments is measured by a NaI（T1） detector.