用于激光驱动质子束测量的腔式束流位置探测器模拟研究

根据激光驱动质子束流低发射度、短脉冲、单束团低电量的性质,研究腔式束流位置探测器(BPM)测量激光加速器产生的质子束团横向位置的可行性问题。针对质子束团的大横向分布和发散角问题,推导了其通过腔式BPM的输出信号,结果表明该信号与集中从束团对称中心、倾斜一定角度通过的束流产生的输出信号相同。依据上述原理,使用CST软件进行了腔式BPM的设计和仿真,确定了矩形谐振腔波导耦合的方案。讨论了该方案的腔式BPM对于激光加速束流的适用性和不同激光驱动质子束流参数的分辨率,并针对PW级激光加速系统进行了分辨率估算。     

速调管放大器大漂移管尺寸输入腔的3维分析与模拟

设计了3种耦合孔结构的大漂移管输入腔,分析比较了其冷腔场分布以及直流电子束通过输入腔间隙后的束流调制情况.计算结果表明:在工作模式下,开单扇形耦合孔和环形孔比开双扇形耦合孔的间隙场均匀;在大尺寸漂移管条件下,采用环形耦合孔输入腔的品质因数比单扇形耦合孔输入腔的小,环形耦合孔输入腔与微波注入波导匹配较好;在相同注入微波功...     

微波电子枪外回路耦合度计算与实验研究

在热阴极微波电子枪的研制中, 为设计微波腔链与波导的耦合孔, 应用Derun Li等提出的``能量方法'进行模拟计算. 使用MAFIA计算微波电子枪第3腔与外回路馈电波导之间的耦合度, 从而设计连接波导与腔链的耦合孔, 使两者之间的耦合度满足需要. 该方法的计算结果与实验测量值的差别在10%—30%之间,满足 实际加工要求. 说明其对于驻波加速腔链与外回路耦合的设计计算是相当有效的.     

非均匀加速结构腔间耦合系数模拟计算

电子直线加速器的聚束段对于会聚入射电子相位,提高电子直线加速器出射束流性能起着至为关键的作用. 而准确计算聚束段腔间耦合系数又是设计聚束段耦合孔几何结构的关键. 本文利用电磁场计算软件MAFIA的特征值计算模块E模块, 分别计算出单腔频率, 双腔腔链的两个本征频率,从而得到聚束段腔间耦合系数. 采用该方法,可以设计聚束段腔间耦合孔的几何参数. 与实验结果的对照表明, 这是一种非常有效的非均匀加速结构腔间耦合孔设计方法.     

可调电子束注入器调配调谐结构的设计及分析

驻波谐振腔是基于直线加速器的束流注入器的基本构造元件,其大功率微波馈入一般选用矩形波导耦合器,但它会引起场不对称和谐振频率的漂移,也难以针对不同流强的束流灵活调节耦合度。建立了带有调配杆的耦合器的等效电路模型,在理论分析的基础上,给出了杆的最佳位置。此外,在耦合器的对称方向插入调谐杆用于补偿结构改变及加工安装等外部因素造成的频率漂移,并使用 CST MICROWAVE STUDIO 的三维电磁仿真给出了两个杆的尺寸和调整范围。联合调整的仿真结果表明,在谐振频率保持稳定的情况下,不同流强的束流均达到临界耦合状态,从而避免了耦合器失配引起的反射功率风险,并减少了由于较小耦合孔引起的场不对称。     

基于自由电子激光的小型太赫兹源初步设计

介绍了基于自由电子激光的太赫兹源的研究情况,提出了一种小型自由电子激光太赫兹源设计方案.采用独立调谐双腔热阴极微波电子枪,不需要α-磁铁及其他束团压缩装置,能够达到所需的束流品质,达到减小系统尺寸的目的.加速结构采用对称输入耦合器和同轴吸收负载输出耦合器,减少加速器的横向尺寸.采用混合永磁型波荡器,孔耦合输出的稳定球面光学谐振腔.介绍了该方案的初步设计和仿真计算.     

可调电子束注入器调配调谐结构的设计及分析（英文）

驻波谐振腔是基于直线加速器的束流注入器的基本构造元件，其大功率微波馈入一般选用矩形波导耦合器，但它会引起场不对称和谐振频率的漂移，也难以针对不同流强的束流灵活调节耦合度。建立了带有调配杆的耦合器的等效电路模型，在理论分析的基础上，给出了杆的最佳位置。此外，在耦合器的对称方向插入调谐杆用于补偿结构改变及加工安装等外部因素造成的频率漂移，并使用CST MICROWAVE STUDIO的三维电磁仿真给出了两个杆的尺寸和调整范围。联合调整的仿真结果表明，在谐振频率保持稳定的情况下，不同流强的束流均达到临界耦合状态，从而避免了耦合器失配引起的反射功率风险，并减少了由于较小耦合孔引起的场不对称。     

SESRI 300 MeV同步加速器注入线的传输效率与接受效率

为了完成SESRI300MeV同步加速器的束流调试,使用Tracewin软件和加速腔电磁场分布文件建立了该加速器注入线从离子源出口到注入点的全尺寸模型,在多粒子模式下计算了两种典型粒子束(质子、²⁰⁹Bi³²⁺)在不同状态下的加速传输,得到了注入线上束流相空间的变化过程和注入线的传输效率与接受效率.研究结果表明,300 MeV同步加速器注入线在加速不同荷质比的离子束流时,电磁场参数设置基本与荷质比成反比.束流的接受效率主要由射频四极加速腔出口发射度决定,质子束和重离子束的接受效率差别较大.在射频四极加速腔出口发射度为0.1πmm·mrad时,²⁰⁹Bi³²⁺束接收效率达到92.13%,质子束的接收效率为68.18%.分析束流传输过程表明,当横向发射度过大时,束流会因为纵向能散展宽和相位展宽而无法被最终接受.在现有配置下,质子束存在横向聚焦力不够、接受效率较低的问题.通过额外增加2个四极铁能够将质子束的接受效率由68.18%提升至83.61%.     

中国散裂中子源直线射频功率源系统的研制

中国散裂中子源加速器质子束流加速能量为1.6 GeV,重复频率为25 Hz,撞击固体金属靶产生散射中子,一期工程的打靶束流功率为100 kW。直线加速器的设计束流流强为15 mA,输出能量为81 MeV。射频加速和聚束系统包括一台射频四极场加速器、中能束流传输线的两个聚束器、四节漂移管直线加速器加速腔和直线-环束流传输线的一个散束器,与之相对应,共有8个单元在线运行的射频功率源为其提供所需的射频功率。目前,直线射频功率源系统预研项目已全部完成,各项性能参数均已达到设计指标,当前正处在批产安装调试阶段。151013     

环形加速器中产生局部斜四极磁场的若干方法

本文研究了环形加速器中产生局部斜四极磁场的若干方法.它用来探索消除束流横向运动耦合所需要的斜四极磁场合适的方位和量值.并以BEPC为例,给出计算的结果.     

Use of multimode cavities with equidistant spectrum for increasing the energy accumulation rate of particles in linear supercolliders

We propose a new accelerating structure for teraelectronvolt linear electron–positron colliders [1–4]. The structure is based on acceleration of a sequence of particle bunches (accelerated beam) by means of a periodic system of quasioptical cavities. Each cavity is operated at several eigenmodes with equidistant frequencies which are excited by a drive beam bunched with the same spatial period as the accelerated beam. The accelerating field represents a time-periodic sequence of narrow peaks separated by wide intervals of a field close to zero. This makes it possible to significantly decrease the effective time of exposure of the structure surface by ultrahigh microwave fields compared with the single-frequency structure. To maximize filling of the structure by accelerating-field regions and minimize ohmic losses, we suggest using a set of modes with a nonzero number of longitudinal variations strictly proportional to the frequencies of these modes. Such modes are able to provide long effective interaction of the total microwave field with a bunch of particles passing across the cavity. In this way, the acceleration gradient averaged over the structure length can be increased. A variant of the accelerating structure which is based on two-mirror cavities with small curvature of the mirrors is proposed. Such cavities can provide approximate frequency equidistance of a large number of modes with nonzero longitudinal variations.     

感应加速腔横向阻抗模拟计算

束腔相互作用导致的束流崩溃不稳定性 (BBU)将严重地恶化束品质 ,而加速腔横向阻抗反映了这种相互作用的强弱。用 MAFIA程序对三种不同的感应加速的腔横向阻抗进行了模拟计算。计算结果与采用脉冲双线法测量的结果反映了相同的物理性质。     

强流直线感应加速腔微波特性

 介绍了确定不同加速间隙形状和设计结构的强流直线感应加速腔微波特性的方法,即确定频域中加速腔横向阻抗值的方法,包括数值模拟和实验测试。 横向阻抗测试实验中采用了两种测试方法:一种为同轴线束流模拟法,另一种为对加速腔形状因子的测试。实验中测试了3种不同的腔型,并和数值模拟结果进行了比较。两种横向阻抗的测试方法所得结果都与计算结果基本符合,从测试过程的繁简程度和多次实验结果的重复性来看,对于强流直线感应加速腔来说,形状因子值测试方法优于双芯同轴线束流模拟法。实验测试和数值模拟结果显示,确定直线感应加速腔横向阻抗值,测试实验和数值模拟是相辅相成的,缺一不可。     

Optimization of the three-dimensional electric f ield in IH-DTL

The tuning process of the three-dimensional electric field near the beam axis is very important in the optimization of the Interdigital H-mode Drift Tube Linac (IH-DTL). The tuning of the longitudinal field distribution, the Kilpatrik (Kp) factor, and the transverse dipole field have been discussed in detail, combined with the radio-frequency tuning process of the 53.667 MHz short IH-DTL cavity, which was designed to accelerate ²³⁸U³⁴⁺ from 0.143 MeV/u to 0.289 MeV/u in the SSC-Linac injector project at the Institute of Modern Physics. The flatness criterion and the tube tuning method are discussed in order to meet the beam dynamics requirements. In the tube tuning process, the energy gain error in the cells should be reduced to less than ±2%, and the Kp factor should be reduced to 1.6. The transverse dipole field and the method that uses a "plunger" to dismiss this dipole field are evaluated. The experience gained from the first cavity optimization benefits the tuning process of the three remaining IH-DTL cavities in the SSC-Linac project.     

双共焦波导结构二次谐波太赫兹回旋管谐振腔设计

准光共焦波导具有功率容量大、模式密度低的特点,能够有效地减少模式竞争对回旋管互作用的影响,有利于高次谐波太赫兹回旋管的设计.为提高太赫兹准光回旋管的互作用效率,在共焦柱面波导的基础上,研究了一种新型高频互作用结构——双共焦波导结构,设计了一种330 GHz二次谐波双共焦结构回旋管谐振腔并对其进行了理论分析和粒子模拟.研究结果表明,双共焦谐振腔中的高阶模式能够与高次电子回旋谐波发生稳定的相互作用,并且没有模式竞争现象,具备工作在太赫兹波段的潜力.相比普通共焦波导谐振腔,双共焦谐振腔能够增强准光回旋管的注波互作用强度,提高回旋管的输出功率和工作效率.此外,结果还表明双共焦波导中的电磁波模式是一种由两个独立的共焦波导模式叠加而成的混合模式.利用这种混合模式有望实现太赫兹回旋管的单注双频工作,为新型太赫兹辐射源的研究提供了新的途径.     

Different optical properties in different periodic slot cavity geometrical morphologies

In this paper,optical properties of two-dimensional periodic annular slot cavity arrays in hexagonal close-packing on a silica substrate are theoretically characterized by finite difference time domain(FDTD) simulation method.By simulating reflectance spectra,electric field distribution,and charge distribution,we confirm that multiple cylindrical surface plasmon resonances can be excited in annular inclined slot cavities by linearly polarized light,in which the four reflectance dips are attributed to Fabry–Perot cavity resonances in the coaxial cavity.A coaxial waveguide mode TE11 will exist in these annular cavities,and the wavelengths of these reflectance dips are effectively tailored by changing the geometrical pattern of slot cavity and the dielectric materials filled in the cavities.These resonant wavelengths are localized in annular cavities with large electric field enhancement and dissipate gradually due to metal loss.The formation of an absorption peak can be explained from the aspect of phase matching conditions.We observed that the proposed structure can be tuned over the broad spectral range of 600–4000 nm by changing the outer and inner radii of the annular gaps,gap surface topography.Meanwhile,different lengths of the cavity may cause the shift of resonance dips.Also,we study the field enhancement at different vertical locations of the slit.In addition,dielectric materials filling in the annular gaps will result in a shift of the resonance wavelengths,which make the annular cavities good candidates for refractive index sensors.The refractive index sensitivity of annular cavities can also be tuned by the geometry size and the media around the cavity.Annular cavities with novel applications can be implied as surface enhanced Raman spectra substrates,refractive index sensors,nano-lasers,and optical trappers.     

Axisymmetric Waves in Re-Entrant Cavities

We employ a well-established method to determine the dispersion properties of transverse magnetic and transverse electric waves in re-entrant cavities. We assume that the waveguide structure consists of a large number of identical cavities in order that the Floquet theorem could be applied to describe the electromagnetic field in an empty cylinder. Furthermore, we describe the electromagnetic field in each cavity region by an eigenfunction expansion for standing waves. Inferring boundary conditions leads to a system of two infinite sets of equations, which is solved numerically by truncation. A numerical code has been developed to calculate the dispersion relation and the electromagnetic field components. Numerical results are presented for several waveguide geometries, including the case of the real gyrotron beam-tunnel geometry. A comparison with already established codes is made.     

The development of a superconducting traveling wave accelerating cavity with high gradient

The required accelerating gradient in the ILC project is over 30 MeV/m [1]. For current technology, the maximum accelerating gradient in superconducting (SC) structures is limited mainly by the value of the surface RF magnetic field. In order to increase the gradient, the RF magnetic field is distributed homogeneously over the cavity surface (low-loss structure), and coupling to the beam is improved by introducing aperture and cell shape (re-entrant structure). These features allow gradients in excess of 56 MeV/m to be obtained for a single-cell cavity. Further improvement of the coupling to the beam may be achieved by using a traveling wave (TW) SC structure with small phase advance per cell. Calculations show that an additional gradient increase by up to 46% is possible if a π/2 TW SC structure is used. However, a TW SC structure requires a SC feedback waveguide to return the few GW of circulating RF power from the structure output back to the structure input. We discuss variants of the superconducting traveling wave ring (STWR) with one and two feeding couplers. The text was submitted by the authors in English.     

环形狭缝腔阵列光学特性的研究

设计了一种六角密排的二维环形纳米腔阵列结构, 利用时域有限差分算法对该结构的光学特性进行了探究. 仿真结果表明, 在线性偏振光入射时, 环形腔内可以形成多重圆柱形表面等离激元谐振, 谐振波长的个数和大小与环形腔的结构参数相关. 根据透、反射光谱, 电场矢量的模式分布及截面电荷密度的分布, 谐振波长处形成圆柱形表面等离激元, 谐振波长处入射光能量大部分在环形腔内损耗, 此时反射率为极小值, 环形腔内的电场增强效应为极大值(光强增强可达1065倍). 谐振波长与环形腔的结构参数(狭缝内径、狭缝外径、膜厚、环境介质折射率、金属的材质)相关, 通过调节结构参数, 谐振波长在350–2000 nm范围内可调. 通过对比相同结构参数的单个环形腔和环形腔阵列的仿真结果, 周期排布对环形腔内的圆柱形表面等离激元吸收峰位置影响不明显. 该结构反射光谱对入射光电矢量偏振方向不敏感. 谐振波长的可调控性对于表面拉曼增强和表面等离激元共振传感器的设计与优化具有指导性意义, 且应用于折射率传感器时灵敏度可达1850 nm/RIU.     

横向运动对驻波加速管电子反轰的影响

驻波加速管的电子反轰除和各种纵向运动因素有关外,还和横向运动因素有关。本文分析了横向运动因素对电子反轰的影响,指出由于横向运动,最终作反向运动的电子只有一部分能反轰到电子枪阴极表面,本文给出了计算反轰束流包络、反轰率、反轰电流及反轰功率的方法。