Preliminary design and simulation of a 162.5 MHz high- intensity proton RFQ for an accelerator driven system

A new procedure for the design and simulation of a Radio Frequency Quadrupole (RFQ) accelerator has been developed at the Argonne National Laboratory. This procedure is integrated with the beam dynamics design code DESRFQ and the simulation code TRACK, which are based on three-dimensional field calculations and the particle-in-cell mode beam dynamics simulations. This procedure has been applied to the development of a 162.5 MHz CW RFQ which is capable of delivering a 10 mA proton beam for the Accelerator Driven System (ADS) of the CAS. The simulation results show that this RFQ structure is characterized by the stable values of the beam acceleration efficiency for both the zero current beam and space charge dominated beam. For an average beam current of 10 mA, there is no transverse rms emittance growth, the longitudinal rms emittance at the exit of RFQ is low enough and there is no halo formation. The beam accelerated in the RFQ could be accepted easily and smoothly by the following super-conducting linear accelerator.     

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 efficiency(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.     

SSC-LINAC重离子RFQ动力学模拟与研究

采用多粒子跟踪程序BEAMPATH 对SSC-LINAC 重离子RFQ 直线加速器进行动力学模拟,分别对RFQ 的接受度、高频特性、束流稳定性、空间电荷效应等进行了分析。该RFQ具有很大的纵向接受度,有利于束流在RFQ中的传输;高频特性研究表明,翼间电压设定在理论值以上时,该RFQ都能保持较好的束流特性;束流稳定性分析结果表明,该RFQ具有很大的束流失配容忍度;空间电荷效应研究表明,当束流强度低于0.5 mA时,束流传输不受影响。综合研究结果表明,53.667 MHz重离子RFQ具有较好的动力学特性,满足SSC-LINAC直线加速器的设计要求。The RFQ beam dynamics of a heavy ion linac was investigated in this paper and the BEAMPATH code was employed in this study. The main research was focused on the beam performances depending on longitudinal acceptance, RF properties, beam instability and space charge effect. The RFQ has large longitudinal acceptance in design, which brings the beam performances well. In the RF parameter study, the beam can keep good transmission in the acceleration even the vane voltage is larger than the theoretical value. It is also shown that the RFQ has a large robustness for the mismatch of the input beam by the analysis of the beam instability.Furthermore, the beam evolution is independent on the space charge effect when the beam current is less than 0.5 emA. The preliminary analysis of the beam dynamics shows that the 53.667 MHz heavy ion RFQ has a promising performance, which meets the requirements of SSC-LINAC.     

Preliminary design and simulation of a 162.5 MHz high-intensity proton RFQ for an accelerator driven system

A new procedure for the design and simulation of a Radio Frequency Quadrupole (RFQ) accelerator has been developed at the Argonne National Laboratory. This procedure is integrated with the beam dynamics design code DESRFQ and the simulation code TRACK, which are based on three-dimensional field calculations and the particle-in-cell mode beam dynamics simulations. This procedure has been applied to the development of a 162.5 MHz CW RFQ which is capable of delivering a 10 mA proton beam for the Accelerator Driven System (ADS) of the CAS. The simulation results show that this RFQ structure is characterized by the stable values of the beam acceleration efficiency for both the zero current beam and space charge dominated beam. For an average beam current of 10 mA, there is no transverse rms emittance growth, the longitudinal rms emittance at the exit of RFQ is low enough and there is no halo formation. The beam accelerated in the RFQ could be accepted easily and smoothly by the following super-conducting linear accelerator.     

Beam Dynamics Design of a 50 mA D~+ RFQ

A new 973 project was proposed by Peking University and Institute of Modern Physics of Chinese Academy of Sciences recently.The project requires a 50 mA,162.5 MHz,cw mode radio frequency quadrupole(RFQ)to accelerate the D~+ to 1 MeV.In a high-current linear accelerator,the strong space charge effect causes the growth of envelope and emittance along with heavy beam losses.In the beam dynamics design of this RFQ,beam envelope mismatching is discussed and a matching dynamics method is proposed to minimize the envelope and emittance growth.The influence of limiting current on the beam transmission is discussed and used in the optimization of transverse and longitudinal parameters.After the optimization,the beam transmission efficiency reaches higher than 98%.     

Power test of the separated function RFQ accelerator

The progress of the Separated Function RFQ (SFRFQ) accelerator, which can raise the field gradient of acceleration while maintaining the transverse focusing power sufficient for high current beam, is presented. In order to demonstrate the feasibilities of the novel accelerator, a prototype cavity was designed and constructed. Correspondingly, a code SFRFQCODEV1.0 was developed specially for cavity design and beam dynamics simulation. The prototype cavity will be verified as a post-accelerator for ISR RFQ-1000 (Integral Split Ring RFQ) and accelerate O+ from 1 MeV to 1.6 MeV. To inject a higher current oxygen beam for the prototype cavity, the beam current of ISR RFQ-1000 was upgraded to 2 mA. The status of high power and beam test preparation for the prototype cavity are presented in this paper.     

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.     

A particle-in-cell mode beam dynamics simulation of medium energy beam transport for the SSC-Linac

A new linear accelerator system, called the SSC-Linac injector, is being designed at HIRFL (the heavy ion research facility of Lanzhou). As part of the SSC-Linac, the medium energy beam transport (MEBT) consists of seven magnetic quadrupoles, a re-buncher and a diagnose box. The total length of this segment is about 1.75 m. The beam dynamics simulation in MEBT has been studied using the TRACK 3D particle-in-cell code, and the simulation result shows that the beam accelerated from the radio frequency quadrupole (RFQ) matches well with the acceptance of the following drift tube linac (DTL) in both the transverse and longitudinal phase spaces, and that most of the particles can be captured by the final sector focusing cyclotron for further acceleration. The longitudinal emittance of the RFQ and the longitudinal acceptance of the DTL was calculated in detail, and a multi-particle beam dynamics simulation from the ion source to the end of the DTL was done to verify the original design.     

整体分离环RFQ加速器的研究

阐述了北京大学整体分离环高频四极场（ＩＳＲＲＦＱ）加速器研究所取得的研究成果．分别论述了２６ＭＨｚ３００ｋｅＶＩＳＲＲＦＱ加速器结构、束流动力学设计、高频控制系统、束流试验装置及束流试验；分析了其对Ｎ＋、Ｏ＋、Ｏ－束流试验的研究结果；简述了２６ＭＨｚ１ＭｅＶＲＦＱ加速器束流动力学、加速腔设计及目前的进展 The status of the ISR RFQ accelerators in Peking University is described. The structure of ISR RFQ accelerator, beam dynamics calculation results by PARMTEQ, RF systems, beam transport lines and the beam test evolutions of a 26 MHz 300 keV ISR RFQ accelerator are also presented, respectively. The beam test results for N +, O +, O - particles are analyzed in detail. At last, the development of 1 MeV 26 MHz ISR RFQ accelerator is introduced briefly.     

Power test of the separated function RFQ accelerator

The progress of the Separated Function RFQ (SFRFQ) accelerator, which can raise the field gradient of acceleration while maintaining the transverse focusing power sufficient for high current beam, is presented. In order to demonstrate the feasibilities of the novel accelerator, a prototype cavity was designed and constructed. Correspondingly, a code SFRFQCODEV1.0 was developed specially for cavity design and beam dynamics simulation. The prototype cavity will be verified as a post-accelerator for ISR RFQ-1000 (Integral Split Ring RFQ) and     

Particle-in-cell mode beam dynamics simulation of the low energy beam transport for the SSC-linac injector

A new SSC-linac system (injector into separated sector cyclotron) is being designed in the HIRFL (heavy ion research facility of Lanzhou). As part of SSC-Linac, the LEBT (low energy beam transport) consists of seven solenoids, four quadrupoles, a bending magnet and an extra multi-harmonic buncher. The total length of this segment is about 7 meters. The beam dynamics in this LEBT has been studied using three-dimensional PIC (particle-in-cell) code BEAMPATH. The simulation results show that the continuous beam from the ion source is first well analyzed by a charge-to-mass selection system, and the beam of the selected charge-to-mass ratio is then efficiently pre-bunched by a multi-harmonic buncher and optimally matched into the RFQ (radio frequency quadrupole) for further acceleration. The principles and effects of the solenoid collimation channel are discussed, and it could limit the beam emittance by changing the aperture size.     

Design studies of a high-current radiofrequency quadrupole for accelerator-driven systems programme

A 3 MeV, 30 mA radiofrequency quadrupole (RFQ) accelerator has been designed for the low-energy high-intensity proton accelerator (LEHIPA) project at BARC, India. The beam and cavity dynamics studies were performed using the computer codes LIDOS, TOUTATIS, SUPERFISH and CST microwave studio. We have followed the conventional design technique with slight modifications and compared that with the equipartitioned (EP) type of design. The sensitivity of the RFQ to the variation of input beam Twiss-Courant parameters and emittance has also been studied. In this article we discuss both design strategies and the details of the 3D cavity simulation studies.     

APTR质子同步加速器RFQ直线注入器的优化设计

为实现质子治疗装置的国产化和小型化,基于已完成安装调试的上海先进质子治疗装置(APTR),开展质子治疗注入器系统的升级设计研究,利用PARMTEQM设计软件和快聚束策略,针对APTR同步加速器RFQ直线注入器进行动力学设计模拟。RFQ工作频率为325 MHz,流强18 mA,对从离子源引出的低能质子束流进行匹配俘获、横向聚焦、纵向聚束和预加速,引出能量为3.0 MeV。通过优化预注入器RFQ动力学设计方案和极头参数,有效避免参数共振,减小束流损失,使其整体传输效率达到98.0%,在水平和垂直方向上的发射度增长分别为1.2%和3.3%,出口束流满足下一级腔体的注入需求,开展设计模拟验证和相关冗余度分析,为质子同步加速器的治疗设备和直线注入系统提供参照依据。     

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.     

973 RFQ 水冷调谐系统(英文)

由于束流的传输效率对射频四极场加速器(RFQ) 中射频场的分布极其敏感,所以在RFQ 的运行过程中不再采用传统的调谐器调谐RFQ。水冷调谐的方法基本上不影响RFQ 射频场的分布,所以适用于RFQ 的调谐。中国科学院高能物理研究所为C-ADS、CSNS 预研RFQ 项目开发建造了一套水冷调谐系统,使用RF 相位差作为控制量进行RFQ 水冷调谐,相位差的控制精度达到了1°运行结果显示该系统满足了RFQ 的调谐需求。介绍了该系统的水冷系统、调谐控制系统和一些运行经验。Since the beam transmission of a Radio Frequency Quadrupole(RFQ) Accelerator is very sensitive to the field profile, the ordinary frequency tuning method by the local movable tuner is no more adopted in an RFQ operation. The tuning method by controlling cooling water temperature is widely adopted to tune the RFQ due to the less affect on the RFQ field profile. A Resonance Control Cooling System (RCCS) is developed and commissioned for the 973 RFQ,which is a R&D project for C-ADS and CSNS RFQ at IHEP. This system adopts the RF phase difference as control variable to tune the RFQ. The control accuracy of the RF phase difference is about 1°. The running of the 973 RFQ shows that the RCCS works very well and fully satisfies the operation requirement of the RFQ. In this paper, the water skid, resonance control system of the RCCS and the operation experiences will be presented.     

IH型漂移管直线加速器的束流动力学研究（英文）

为了提高兰州重离子加速器冷却储存环（HIRFL-CSR）的运行效率、改善加速器输出束流品质,并实现几个加速装置分时供束,提高整个重离子加速装置的利用率,特为（HIRFL-CSR）增建一台新的注入器--CSRLINAC。在108.48 MHz的RFQ之后的CSR-LINAC主加速段,主要由一台108.48 MHz和两台216.96 MHz的IH型漂移管直线加速器组成,用于加速荷质比为1/8.5~1/3之间的重离子,其最大的束流流强为3 mA,并将粒子从0.3 MeV/u加速到3.71 MeV/u。运用KONUS动力学原理,在满足设计指标的情况下,首先利用TraceWin程序进行中能束线MEBT设计,后针对高频腔体设计和束流匹配的基本参数的系列讨论,特别是对CSR-LINAC的中能束流匹配线、参数选择和IH型KONUS结构的漂移管直线加速器进行设计模拟优化。最终得出,在保证腔体设计指标和95.3%的传输效率的情况下,该紧凑型直线加速结构经过三个腔体的加速后,束流的纵向归一化均方根发射度增长仅有25%;同时发现,当流强达到3 mA时,存在空间电荷效应,导致其纵向相宽增长约25%,最大横向包络也存在16.5%的涨落。In order to improve the operation efficiency of the Cooling Storage Ring of Heavy Ion Research Facility in Lanzhou (HIRFL-CSR), a heavy ion linac (linear accelerator) was proposed and designed as a new injector for HIRFL-CSR. Following the 108.48 MHz Radio-Frequency Quadrupole (RFQ), three tanks in total with Interdigital H-mode drift tube linac (IH-DTL) structure are installed to boost the beam energy from 0.3 to 3.71 MeV/u, and the beam current of ions with charge-to-mass ratio from 1/8.5 to 1/3 can reach to 3 mA. The first tank operatesat the same frequency as the RFQ, and the rest two operate at 216.96 MHz. The “Combined Zero-Degree Synchronous Particle Structure” (KONUS) beam dynamics was used in the beam dynamics design. The overview of the physics design on the main accelerating components, including RF design and beam dynamics design are introduced in this paper. The optimized structure design, fabrication status and simulation results are presented in this contribution. It shows that under the condition of assurance of 95.3% transmission efficiency, the normalized rms emittance is about 25%. When the beam current is up to 3 mA, owing to the space charge effect, the increase of longitudinal phase spread and transverse envelope are about 25% and 16.3%, respectively.     

Numerical optimization and multi-particle dynamics simulation of the radial matching section of the RFQ

The ABC code is an optimization program for the development of matching channels and dynamical matchers in radio frequency quadrupole (RFQ) structures, and a new approach to this code to define the geometry of the radial matching section of the RFQ has been developed. This approach is based on the application of the numerical optimization step by step. This optimization is intended to search for the initial matching condition of a beam, the optimization of parameters of a cell of the channel on given characteristic parameters and traces of a beam in linear channels in both forward and backward directions. To further verify the results of the optimization, multi-particle beam dynamics simulations have been carried out using the BEAMPATH and TRACK codes. The result of the beam dynamics simulation shows that the optimization result of the ABC code is reasonable and this approach provides an opportunity to redesign the structure of the radial matching section of the RFQ.     

Studies on RFQ accelerators and its applications

Development activities of Radio Frequency Quadrupole (RFQ) accelerators in China are presented.A 1 MeV O~+ RFQ and a 3.5 MeV ADS proton RFQ have been constructed.A novel separated function RFQ is under beam test, a 2 MeV D~+ RFQ is under construction and a CSNS RFQ is going to be constructed.The RFQ dynamics and the simultaneous dual beam acceleration with positive and negative ions were investigated and related codes were developed.The applications of RFQ will be further promoted in China.     

Beam dynamics and RF design of trapezoidal IH-RFQ with low energy spread

Beam dynamics and RF design have been performed of a new type trapezoidal IH-RFQ operating at 104 MHz for acceleration of ¹⁴C⁺ in the framework of RFQ based ¹⁴C AMS facility at Peking University. Low energy spread RFQ beam dynamics design was approached by the method of internal discrete bunching. ¹⁴C⁺ will be accelerated from 40 keV to 500 keV with the length of about 1.1 m. The designed transmission efficiency is better than 95% and the energy spread is as low as 0.6%. Combining the beam dynamics design, a trapezoidal IH-RFQ structure was proposed, which can be cooled more easily and has better mechanical performance than traditional RFQ. Electromagnetic field distribution was simulated by using CST Microwave Studio (MWS). The specific shunt impedance and the quality factor were optimized primarily.     

Beam dynamics and RF design of trapezoidal IH-RFQ with low energy spread

Beam dynamics and RF design have been performed of a new type trapezoidal IH-RFQ operating at 104 MHz for acceleration of 14C+ in the framework of RFQ based 14C AMS facility at Peking University. Low energy spread RFQ beam dynamics design was approached by the method of internal discrete bunching. 14C+ will be accelerated from 40 keV to 500 keV with the length of about 1.1 m. The designed transmission efficiency is better than 95% and the energy spread is as low as 0.6%. Combining the beam dynamics design, a trapezoidal IH-RFQ structure was proposed, which can be cooled more easily and has better mechanical performance than traditional RFQ. Electromagnetic field distribution was simulated by using CST Microwave Studio (MWS). The specific shunt impedance and the quality factor were optimized primarily.