抑制超短电子脉冲展宽的补偿方法

 提出了一种有效的利用补偿元件抑制空间电荷效应所致脉冲展宽的方法。此元件为一轴对称的圆柱形空腔,金属侧壁和供脉冲输出的端面金属栅网接地以保持0电位,供脉冲进入空腔的端面小孔的内壁涂导电层并施以正电位,通过选择此端面的介电常数分布而在此端面上形成特定的电位分布。如此形成的补偿元件内部电场能够在不引入附加电子能量弥散的基础上,在空点电荷效应所致脉冲展宽极为严重的纵向和横向这两个主要方向上,均能够有效地抑制空间电荷效应,从而起到补偿电子脉冲展宽的作用。     

氟聚合物压电驻极体的压电性及其电荷的动态行为

描述了一种可控微结构的多孔聚合物压电功能膜的制备方法,讨论了采用该工艺制备的聚四氟乙烯(PTFE)和全氟乙丙烯共聚物(FEP)复合膜压电驻极体的压电性能及其热稳定性.通过等温压电系数衰减和短路热刺激放电(TSD)方法,研究了氟聚合物复合膜压电活性热稳定性改善的根源,以及脱阱电荷输运和复合的特性.结果表明,这类氟聚合物压电驻极体膜的准静态压电系数d₃₃可高达2200pC/N;压电系数d₃₃的压强特性在直到20kPa的压强范围内呈现良好的 关键词： 氟聚合物 压电驻极体 热稳定性 电荷动态特性     

开路光伏空间孤子的动态行为

从理论上研究了开路情况下一维光伏空间孤子的时间演化过程.采用数值方法,通过研究有无背景光辐照下光伏空间亮(暗)孤子的含时空间电荷场,分别得到了光伏空间亮(暗)孤子的孤子波形强度微分方程.在此基础上研究了开路情况下通过增加均匀背景光辐照强度对光伏空间孤子及其半峰全宽的影响.结果显示,通过增加均匀背景光辐照强度,光伏空间孤子随时间的演化过程比没有均匀背景光时加快的倍数为均匀背景光强与暗辐照光强之比.光伏空间孤子的半峰全宽达到稳态所需的时间随孤子峰值强度和暗辐照与均匀背景光强度之和的比值的增大而变短.     

CSNS-II双谐波加速研究

The Rapid Cycling Synchrotron （RCS） of the China Spallation Neutron Source （CSNS） complex is designed to provide 1.56×10^13 protons per pulse （ppp） during the initial stage, and it is upgradeable to 3.12× 10^13 ppp during the second stage and 6.24× 10^13 ppp during the ultimate stage. The high beam intensity in the RCS requires alleviation of space charge effects to reduce beam losses, which is key in such high beam power accelerators. With higher intensities in the upgrading phases, a dual-harmonic RF system is planned to produce flat-topped bunches that are useful to reduce the space charge effects. We have studied different schemes to apply the dual-harmonic acceleration in CSNS-Ⅱ, and have calculated the main parameters of the RF svstems, which are presented in this Darter.     

PIC mode simulation of solenoid collimation channel

A new SSC （Separated Sector Cyclotron）-Linac is being designed to serve as an injector for the SSC at the HIRFL （Heavy Ion Research Facility Lanzhou）. The beam intensity at the LEBT （Low Energy Beam Transport） for the heavy ions after the selection is typically low and the space charge effects are inconspicuous. The space charge effects become obvious when the beam current increases to a few hundred microamperes. The emittance growth deriving from the space charge effects may be particularly troublesome for the following linac and cyclotron. An optical system containing three solenoids has been designed for the LEBT to limit the beam emittance and to avoid the unnecessary beam loss in the cyclotron, as well as for the purpose of immunizing the LEBT emittance growth due to the space charge effects. The results of the PIC （Particle- In-Cell） mode simulation illustrate that this channel could limit the beam emittance growth and increase the beam brightness.     

A Particle-in-cell scheme of the RFQ in the SSC-Linac

A 52 MHz Radio Frequency Quadrupole （RFQ） linear accelerator （linac） is designed to serve as an initial structure for the SSC-Linac system （injector into Separated Sector Cyclotron）.The designed injection and output energy are 3.5 keV/u and 143 keV/u,respectively.The beam dynamics in this RFQ have been studied using a three-dimensional Particle-In-Cell （PIC） code BEAMPATH.Simulation results show that this RFQ structure is characterized by stable values of beam transmission effciency （at least 95%） for both zerocurrent mode and the space charge dominated regime.The beam accelerated in the RFQ has good quality in both transverse and longitudinal directions,and could easily be accepted by Drift Tube Linac （DTL）.The effect of the vane error and that of the space charge on the beam parameters have been studied as well to define the engineering tolerance for RFQ vane machining and alignment.     

激光加速质子束空间电荷力研究（英文）

激光加速器可以输出具有独特品质的质子束,例如μm尺寸、ps脉冲长度和高峰值电流。强流粒子束的空间电荷力效应较强,对面向应用的束流传输提出了挑战。通过二维PIC模拟研究了激光加速后与质子速度接近的电子的影响。采用椭球模型估算空间电荷力的影响,比较不同电荷分布的差异。结果表明每束团质子数超过10¹⁰后空间电荷力显著影响质子束传输,甚至严重破坏束流品质。空间电荷力的影响在20 ps后显著减弱,离开靶约1.2 mm。