100-femtosecond MeV electron source for ultrafast electron diffraction

A near-relativistic 100-fs MeV electron beam is developed by using a photocathode rf gun for revealing the hidden ultrafast dynamics of intricate molecular and atomic processes in materials through experimentation of ultrafast time-resolved electron diffraction (UED). The transverse and longitudinal dynamics of femtosecond electron beam in the rf gun were studied theoretically by particle simulation. The growths of the emittance, bunch length and energy spread due to the rf and space charge effects were investigated by changing the laser parameters, field gradient and electron charge. The theoretical studies indicate that a 100-fs MeV electron beam with the transverse emittance of 0.1 mm mrad and the relative energy spread of 10⁻³–10⁻⁴ at bunch charge of 0.1–2 pC (10⁶–10⁷ electrons per pulse) is achievable for UED, in which the intensity is three orders of magnitude higher than that produced by the conventional dc or pulsed guns.     

A Control Simulation Method of High-Speed Trains on Railway Network with Irregular Influence

Based on the discrete time method, an effective movement control model is designed for a group of high-speed trains on a rail network. The purpose of the model is to investigate the specific traffic characteristics of high-speed trains under the interruption of stochastic irregular events. In the model, the high-speed rail traffic system is supposed to be equipped with the moving-block signalling system to guarantee maximum traversing capacity of the railway. To keep the safety of trains' movements, some operational strategies are proposed to control the movements of trains in the model, including traction operation, braking operation, and entering-station operation. The numerical simulations show that the designed model can well describe the
movements of high-speed trains on the rail network. The research results can provide the useful information not only for investigating the propagation features of relevant delays under the irregular disturbance but also for rerouting and rescheduling trains on the rail network.     

冰弹丸高速发射方法研究

冰弹丸的高速发射技术是认识冰弹丸高速撞击靶板损伤效应的瓶颈技术。利用二级轻气炮作为发射装置,采用液氮杜瓦制冷系统实现温度控制,选择铝质膜片对气压进行控制,利用高速摄像机对冰弹丸的完整性进行观测,并利用丝网测速仪对弹丸速度进行测量,实现了对冰弹丸的高速发射。通过实验验证了该方法的可行性,得到了完整冰弹丸在1516m/s下撞击铝合金靶板的实验结果。     

感应耦合等离子体中和枪的电子引出特性研究

给出了一种感应耦合等离子体源的设计,用于等离子体中和枪装置。通过实验方法研究等离子体源的电子引出特性,并结合理论分析了等离子体密度随射频功率的变化关系。研究结果表明等离子体源的电子引出特性与放电腔内气压有关联性,E?H模式转换中电子密度的变化与负载的电感值相关。研究成果对等离子体中和枪的发展有重要的参考价值。     

第三介质作用下坡道对轮轨黏着特性影响

利用JD-1轮轨模拟试验机,通过设计坡道试验夹具实现了不同坡道接触条件的轮轨模拟试验,研究了第三介质条件下坡度对轮轨界面黏着特性的影响规律.结果表明:在干态、水介质和防冻液介质条件下,上下坡道工况的轮轨黏着系数均低于平直轨道工况;随坡道坡度的增加,黏着系数呈下降趋势且下坡道的黏着系数下降更为明显;与水介质相比较,轮轨界面存在防冻液时更容易引起低黏着现象;上坡道工况下,随速度和轴重的增加轮轨界面黏着系数呈略微下降的趋势.     

工艺参数对高铁轴承外圈端面成形质量的影响

为了实现高铁轴承外圈的精确成形, 应用ABAQUS有限元软件, 对不同工艺参数下的冷辗扩轧制过程进行了有限元模拟, 得到了工艺参数对高铁轴承外圈成形质量的影响规律为: 较大的驱动辊转速和芯辊直线进给速度有利于坯料上端面的成形, 较小的轧制比获得的坯料上端面成形质量较好.     

飞秒激光高精细加工柴油机喷油嘴倒锥孔法

利用飞秒激光加工热效应小、高精细、对材料无选择性等特点,针对柴油发动机高压共轨系统中关键零件——喷油嘴偶件喷油孔的加工需求,设计了一种利用三光楔扫描的飞秒激光加工装置,并进行了喷油嘴倒锥孔加工工艺研究.采用微孔三座标测量机(测量准确度1.2μm)对倒锥孔尺寸准确度进行检测,通过喷油嘴高压液体流量试验台(测量准确度±0.1%)对批量制孔后的油嘴进行了流量测试,结果表明:所设计装置加工的油嘴性能可以满足欧V排放法规的应用要求,对提升汽车制造业水平及柴油车排放标准具有重要意义.     

Preliminary design and multipacting simulation of a SRF quarter wave electron gun at Peking University

Peking University is designing a new SRF gun that is composed of a quarter wave resonator （QWR） and an elliptical cavity. Compared to the elliptical cavity, the QWR is sufficiently compact at the same frequency and its electric field is quasi-DC. The RF parameters are determined by optimization of QWR cavity structure and the possible multipacting locations are analyzed by 2D MP simulation. The simulation results show that multipacting is not a critical issue for our optimized cavity structure.     

Preliminary design and multipacting simulation of a SRF quarter wave electron gun at Peking University

Peking University is designing a new SRF gun that is composed of a quarter wave resonator (QWR) and an elliptical cavity. Compared to the elliptical cavity, the QWR is sufficiently compact at the same frequency and its electric field is quasi-DC. The RF parameters are determined by optimization of QWR cavity structure and the possible multipacting locations are analyzed by 2D MP simulation. The simulation results show that multipacting is not a critical issue for our optimized cavity structure.     

Design of an electron gun for terahertz radiation source

An EC-ITC(External-Cathode Independently Tunable Cells) RF gun was employed with the aim of obtaining short-pulse bunches with high peak current for a terahertz radiation source. A gridded DC gun plays a key role as the external injecting electron source of the ITC RF gun, the performance of which determines the beam quality in the injector and transport line. In order to make the beam well compressed in the ITC RF gun, the energy of the electrons acquired from the gridded DC gun should be 15 keV at most. A proper structure of the gridded gun with double-anode is shown to overcome the strong space- charge force on the cathode, which is able to generate 6 μs beam with 4.5 A current successfully.