四轩型RFQ加速腔高频特性的数值模拟与实验研究

为设计一个高负载因子、高流强的RFQ加速器，使用三维电磁场计算程序MAFIA对加速腔的高频特性进行了模拟计算. 本文主要研究RFQ支撑板高度、宽度、间距、电极形状等结构参数对高频腔体高频特性的影响，根据RFQ加速器的比分路阻抗以及电磁场分布的要求，对RFQ的结构参数进行优化设计，然后根据模拟计算结果加工冷模，进行冷模测量并将测量结果与计算结果加以比较.     

RFQ的束流动力学设计研究

本文评述了RFQ直线加速器对于加速低β粒子的重要优越性。给出了它的近轴区内高频电场的分布及粒子运动方程。叙述了束流的俘获效率及纵向相空间分布对于RFQ参数及注入能量的依赖关系。给出了750keV质子RFQ加速器的动力学设计研究。     

强流四杆型RFQ加速腔水冷系统的设计和数值模拟

为了研制一个强中子发生器，北京大学重离子物理研究所设计了一台高负载因子、高流强的RFQ加速器. 本文讨论了RFQ加速腔水冷系统的设计，使用有限元软件ANSYS对水冷系统进行了分析. 使用MAFIA模拟计算得到的功率密度，并将其作为ANSYS水冷模型的边界条件. 因为MAFIA程序和ANSYS程序分网方法的不同，使用一个程序来将MAFIA的结果导入到ANSYS模型中，从而建立起了RFQ加速腔的热分析模型. 通过这个热分析模型分析并检验了水冷系统的设计，确定了水冷系统的结构. 模拟计算结果表明：使用目前设计的这套水冷系统，能够使RFQ加速器工作在适宜的温度下以及长时间稳定的运行.     

分段共振耦合BFQ的调谐与测量

对一长度为3m的分段共振耦合RFQ冷模进行了多次调谐和测量，得到了RF电场平整度好于4％的场分布；解决了分段共振耦合RFQ调谐时捐合单元处RF电场分布出现的台阶问题；确定了分段共振耦合RFQ的调谐步骤。     

中国散裂中子源RFQ的热分析

射频四级场(RFQ)加速器的水冷具有以下两种功用: 首先它可以把射频场发热带走, 维持RFQ腔的热稳定性及限制RFQ强体形变幅度; 其次, 当RFQ失谐时, 它还可以用来进行RFQ的调谐, 而同时又基本不影响RFQ的射频场分布. 由于RFQ粒子的传输效率对射频场的分布极其敏感, 在RFQ的运行中不再采用传统的用调谐器对RFQ进行调谐的方法. 本文通过热分析, 确定了RFQ加速器的水冷管道的数量和布局及最佳工作水温; 确定了RFQ失谐时, 如何利用水温变化来对RFQ进行调谐的方法.     

750 keV射频四极注入器射频结构的优化

 设计了750 keV,201.25 MHz的RFQ注入器的射频结构,对四杆型RFQ结构进行了简要的理论分析,在束流动力学设计的基础上,对射频结构进行了优化。研究了四杆型RFQ结构中支撑板高度、宽度、厚度、间距、形状、外腔体半径等因素对射频特性的影响,进行了优化设计并给出了主要的结构参数及射频特性的设计结果。优化设计得到的四杆型RFQ腔体长度126 cm,在极间电压80 kV时,峰值功率损耗为115.95 kW,二极场因子为1.004,电场沿轴向分布比较均匀,偏差小于3.5%,满足了物理需求。     

分段共振耦合RFQ场调谐方法研究

强流质子加速器需要采用分段共振耦合RFQ作为其低能加速结构,为减少束流损失,RFQ加速器必须达到所要求的场分布.针对共振耦合结构的特殊性,在RFQ传输线模型的理论基础上,在一台RFQ冷模型上进行了场调谐的实验研究,获得了满意的实验结果.同时,也验证了作者用LabVIEW编写的RFQ场调谐程序的正确性.     

四杆与四翼型RFQ内的二极场研究

RFQ (射频四极透镜) 是直线加速器中最重要的前级聚焦加速结构，其工作模式下束流孔中的电场四极对称性是保证束流品质及加速效率的关键。为了解决其各自存在的工作模式下四极场的不对称问题，分别对四杆型RFQ 和四翼型RFQ 的结构和模式谐振特性做了研究。针对四翼型RFQ，模拟显示双端口对称耦合的方式从抵消二极模式和提高结构对称性两方面来达到削弱工作模式下的场分布中二极量的目的，对一个1 m段四翼RFQ 模型腔的测量证实了双端口对称耦合抵消腔内二极模式的有效性；针对四杆型RFQ 的二极场，以SSC-Linac 项目的RFQ 为原型，利用三维模拟计算软件CST-MWS 进行模拟，通过改进支撑板的结构并调整参数，完全地消除了工作模式下的极间二极场，且理论上此种改进方法对支撑板结构的四杆型RFQ 均有效。Radio Frequency Quadruple(RFQ) is the most important front-end acceleration structure in linear accelerators.It can focus and accelerate beam in longitudinal and transversal direction, simultaneously. Symmetric of electric field in acceleration aperture is very important for the beam dynamics. To an idea RFQ, there is only quadruple electric field in the acceleration aperture. The dipole field in aperture is harmful and need be as small as possible. The methods to reduce it are studied in a four-rod RFQ and a four-vane RFQ in the article ndependently. To a four-vane RFQ, the symmetrical double-port couplers are employed to counteract the neighboring dipole modes. The availability is confirmed by the simulation with the 3-D Finite Element tool, CST-MWS. And it is also observed by measuring a model-cavity with a symmetrical double-port couplers. To a four-rod RFQ, a new structure of stems is proposed to reduce the dipole mode.Taking the RFQ for the SSC-LINAC project as example, the dipole mode contributions to the electric filed is completely eliminated by selecting stem’s parameters carefully. It is confirmed by the simulation of CST-MWS. heoretically, this method is independent with the frequency of an RFQ and serves for all RFQs with 4-rod or 4-wane structure.     

分离作用射频四极场加速器的结构和工艺设计

 介绍了北京大学分离作用射频四极场(RFQ)加速器的结构特点,包括膜片式电极、支撑环式电极支撑系统、水冷系统、调谐系统及其工艺实现;介绍了基于该分离作用RFQ加速腔进行的调谐测试、高功率实验和束流实验。结果表明:调谐系统的频率调节范围及品质因数完全满足实验要求;分离作用RFQ加速腔的输入功率可以达到33 kW以上,满足高功率下稳定运行的条件;在束流实验中,把1.03 MeV的O⁺入射束流加速到1.65 MeV,半高宽能散小于3%。加速器结构满足物理设计要求,加速系统运行稳定。     

RFQ加速器的束流动力学和高频结构

本文描述了RFQ加速器的特点.说明了束流动力学设计研究对于形成这些特点的贡献.给出了它的五个设计极限.综述了近10年来国内外在RFQ束流动力学和高频结构方面的若干主要发展.     

CSR-LINAC IH-RFQ的高频电磁设计

中国科学院近代物理研究所在CSR-LINAC项目中设计了一台108.48 MHz的IH型RFQ直线加速器。该RFQ可以将质荷比为3~7的离子从4 keV/u加速到300 keV/u。在完成束流动力学设计的基础上,主要针对RFQ腔体的高频电磁设计展开了研究,同时利用了电磁场仿真和束流动力学模拟来研究腔体的四极场不平整度和二极场及其动力学影响。未经调谐的情况下,腔体的谐振频率为108.15 MHz,腔体空载品质因子Q₀为5 910,腔体功耗为123 kW。通过在支撑板两端增加底切的设计,将腔体的四极场不平整度由-21%~ 12%优化至±2.5%,满足了束流动力学要求。腔体的二极场为-3%~ -2.2%,使得束流在垂直方向小幅振荡,RFQ的垂直方向接受度减小5%。为了保证功率馈入时反射较小,将耦合器设置在临界耦合状态,耦合面积为940 mm2。为了补偿腔体的频率偏差和漂移,设计了调谐量分别为707和132 kHz的固定调谐器和可动调谐器。The 108.48 MHz IH type RFQ for CSR-LINAC project is under design at Institute of Modern Physics, Chinese Academy of Sciences. This RFQ can accelerate heavy ions with mass to charge ratio of 3~7 from 4 keV/u to 300 keV/u. According to the beam dynamics requirement, the RF structure design has been finished. The quadrupole field unflatness and dipole field of the cavity were studied by electromagnetic simulation and beam dynamics simulation. The frequency of the cavity without tuning is 108.15 MHz, the Q₀ of the cavity is 5910, and the RF power loss is 123 kW. The quadrupole field unflatness of ±2.5%,which was -21%~12% before optimizing, is achieved to meet dynamics requirement through the undercuts in cavity supporters. The dipole field of -3%~ -2.2% causes the oscillation of the beam center and acceptance reduction of 5%. The power coupler must be in critical coupling state with the coupling area of 940 mm2 for minimum reflection coefficient. The tuners, consist of coarse and fine tuners with frequency shift of 707 and 132 kHz respectively, is used for tuning of frequency deviation of the cavity.     

强流RFQ的稳定性设计研究

对强流RFQ耦合间隙的确定、二极模稳定杆的设计进行了详细的研究和讨论.利用现有的RFQ冷模,进行了本征模频率的测量、场分布的调试和测量、二极模稳定杆的试验.并通过与模拟结果的比较,验证了模拟程序在RFQ腔体设计中的可靠性.同时,对影响RFQ稳定性设计的物理进行了有益的探讨.     

耦合腔链等效电路模型计算加速管场分布

介绍利用耦合腔链等效电路模型计算加速管场分布的原理和方法. 把加速腔链等效为谐振电路, 通过求解回路方程组, 并引入分流阻抗等物理参数, 可计算加速腔链整管的电磁场幅值和相位分布. 这一计算方法对加速管动力学设计和加速管几何参数设计有很好的指导意义, 并在16MeV返波加速管设计调试过程中得到了应用和验证.     

离子源注入型IH加速腔冷测与调谐

离子源注入型IH加速器有望发展成为一种紧凑型低功耗离子加速器,为有效验证该加速结构的束流俘获效率,中国工程物理研究院流体物理研究所设计了一套将质子束从0.04 MeV加速到2.0 MeV的IH加速腔。目前已经完成了该腔的腔体加工,开展了高频参数冷测及腔体调谐研究。通过漂移管调谐和电感调谐,减小了腔体的频率误差和加速电压分布误差。模拟计算实测电场下腔体的束流俘获效率,由调谐前的16%提高到调谐后的34%。冷测调谐结果表明,该加速腔的各项参数达到设计值,具备进行功率测试和束流测试的条件。     

Lorentz detuning and tuning system study of 3+1/2cell DC-SC photo-injector for PKU-FEL

A 3+1/2cell DC-SC photo-injector for PKU-FEL facility is under development, which is an upgrade design of the successful 1+1/2cell DC-SC photo-injector. The Lorentz detuning and tuning structure for the 3+1/2cell superconducting cavity is presented in this paper. The Lorentz force detuning coefficient is 7.2 Hz/(MV/m)2 with double stiffening rings for the half cell and single stiffening rings between the adjacent TESLA cells. With the special stiffening structure, the 3+1/2cell whole cavity needs only one tuner. The influences of the tuning on frequency shift, field flatness and average gradient are discussed in this paper. The simulation results show that the stiffening rings' design is successful.     

Diode laser extended cavity for broad-range fast ramping

A novel design for an extended-cavity diode laser is presented. The cavity contains an electro-optic prism for synchronous tuning of the cavity length and the grating's incident angle. A simple analysis of the cavity is presented. Experimental results are reported that show mode-hop-free tuning over more than 10 GHz with high linearity and reproducibility. To the authors' knowledge, this is the first demonstration of mode-hop-free tuning of an extended cavity over several free spectral intervals with an electro-optic crystal.     

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.     

基于滑模极值搜索的SSC-LINAC RFQ调谐系统设计与测试

将滑模极值搜索算法引入基于腔体反射信号的SSC-LINAC射频四极场加速器(Radio Frequency Quadrupole, RFQ)腔体频率稳定系统设计中,结合Lyapunov稳定性理论和SSC-LINAC RFQ高频系统的特点,对滑模极值搜索算法的控制增益和参考信号进行改进;通过求解微分方程,得到腔体反射信号关于时间和调谐杆位置的函数。通过软件仿真和设计硬件系统,对基于滑模极值搜索算法的调谐过程进行仿真与实际测试,结果显示,所设计的频率稳定系统能够在较短时间内实现SSC-LINAC RFQ腔体功率自动馈入过程且频率稳定度满足设计指标要求,通过了长时间稳定性试验。证明了将滑模极值搜索算法应用于高频谐振腔调谐工作的可行性。