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.     

一种低能散RFQ加速器的物理设计

讨论了脉冲束注入、逐步增加同步相位、减小电极调制系数和极间电压等降低RFQ加速器能散的途径, 并在此基础上设计了一台能散为0.6%的RFQ加速器. 该加速器用于加速器质谱对¹⁴C, ¹³C, ²C 3种 离子的传输有很强的选择性, 有利于降低测量本底、简化装置.     

Design of medium energy beam transport line between the RFQ and the Linac in the radioactive ion beam facility at VECC,Kolkata

The design of a medium energy beam transport (MEBT) line comprising of a re-buncher and four quadrupoles, two upstream and the other two downstream of the re-buncher, has been presented. The design was done to ensure almost 100% transport of heavy-ion beams of about 99 keV/u energy from RFQ having a q/A not less than 1/14 through the re-buncher and then through IH Linac of about 0.6 m length in which beam would be accelerated to about 185 keV/u. The re-buncher has been designed to operate at 37.8 MHz, the resonating frequency of both the RFQ and the IH Linac. The entire beam line has been installed and recently O⁵⁺ beam from RFQ has been transported through the re-buncher and subsequently accelerated in the IH Linac successfully.     

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.     

Progress in the beam commissioning of separated function RFQ accelerator

Separated Function RFQ (SFRFQ) was proposed as a post accelerator of RFQ to accelerate heavy ions at low frequency. It introduces gap accelerating in the quadrupole electrodes, and therefore it has higher accelerating efficiency than the conventional RFQ accelerator. The first SFRFQ prototype cavity has been specially designed and constructed as a post accelerator to accelerate O+ beam from 1.03 MeV to 1.64 MeV. Based on accomplishment of low power measurement and high power test, the beam commissioning was carried out to verify its feasibility. The measured energy gain per cell of SFRFQ is 45 keV, which is about 60% higher than that of Peking University Integral Split Ring (ISR) RFQ.     

The design of a radio frequency quadrupole LINAC for the RIB project at VECC Kolkata

A radio frequency quadrupole LINAC has been designed for the VECC-RIB project for an input beam energy of 1.0 keV/u and q/A≥1/16. The output energy will be about 90 keV/u for a 3.4 m long, 35 MHz structure. A half-scale cold model of the RFQ has been fabricated and tested for rf structure design study. The beam dynamics and rf-structure design along with the results of the cold model tests 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.     

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.     

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.     

Beam life time studies and design optimization of the Ultra-low energy Storage Ring

The Ultra-low energy electrostatic Storage Ring (USR) at the future Facility for Low-energy Antiproton and Ion Research (FLAIR) will provide cooled beams of antiprotons in the energy range between 300 keV down to 20 keV. Based on the original design concept developed in 2005, the USR has been completely redesigned over the past few years by the QUASAR Group. The ring structure is now based on a ’split achromat’ lattice. This ensures compact ring dimensions of 10 m × 10 m, whilst allowing both, in-ring experiments with gas jet targets and studies with extracted beams. In the USR, a wide range of beam parameters shall be provided, ranging from very short pulses in the nanosecond regime to a coasting beam. In addition, a combined fast and slow extraction scheme will be featured that allows for providing external experiments with cooled beams of different time structure. Detailed investigations into the dynamics of low energy beams, including studies into the long term beam dynamics and ion kinetics, beam life time, equilibrium momentum spread and equilibrium lateral spread during collisions with an internal target were carried out. This required the development of new simulation tools to further the understanding of beam storage with electrostatic fields. In addition, studies into beam diagnostics methods for the monitoring of ultra-low energy ions at beam intensities less than 10 ⁶ were carried out. This includes instrumentation for the early commissioning of the machine, as well as for later operation with antiprotons. In this paper, on overview of the technical design of the USR is given with emphasis on two of the most important operating modes, long term beam dynamics and the design of the beam diagnostics system.     

Study of separated function radio frequency quadrupoles accelerator

SFRFQ (Separated Function Radio Frequency Quadrupoles) accelerator is a new post accelerator of RFQ (Radio Frequency Quadrupoles) type, which has been developed since the beginning of the 1990s at Peking University. In order to demonstrate the possibility of the SFRFQ, a prototype cavity has been designed.A special dynamics design method has been proposed to avoid the sparking problem and decrease the energy spread at the exit of SFRFQ. It consists of two aspects: the asymmetry structure design for transverse focusing and the inner buncher design for longitudinal bunching. This allows the improvement of the beam properties without increasing the cavity length. The simulation results show that the energy spread can be substantially reduced by using the inner buncher in the SFRFQ structure.     

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.     

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.     

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%.     

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 study of RFQ for CADS with a 3D space-charge-effect

The ADS (accelerator driven subcritical system) project was proposed by the Chinese Academy of Sciences. The initial proton beams delivered from an electron cyclotron resonance ion source can be effectively accelerated by 162.5 MHz 4.2 m long room temperature radio-frequency-quadrupoles (RFQ) operating in CW mode. To test the feasibility of this physical design, a new Fortran code for RFQ beam dynamics study, which is space charge dominated, was developed. This program is based on Particle-In-Cell (PIC) technique in the time domain. Using the RFQ structure designed for the CADS project, the beam dynamics behavior is performed. The well-known simulation code TRACK is used for benchmarks. The results given by these two codes show good agreements. Numerical techniques as well as the results of beam dynamics studies are presented in this paper.     

RFQ加速器同时加速同荷质比正负离子的实验研究

阐述了利用北京大学26MHz 300keV整体分离环高频四极场(ISR RFQ)加速器同时加速同荷质比正负离子的研究结果.分别用O⁺和O^－离子的连续束以及脉冲束同时注入,均实现了RFQ加速器对同荷质比正负离子的同时加速.用快靶测得的经RFQ腔同时加速后形成的O⁺及O^－离子微脉冲束与预想的正负氧离子微脉冲束相位关系完全一致.证实了同时加速时得到的氧离子束总和明显高于单加速一种离子时得到的氧离子束.在国际上首次实现了用RFQ加速器同时加速同荷质比的正负离子.     

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.     

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.