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 new compact structure for a high intensity low-energy heavy-ion accelerator

A new compact accelerating structure named Hybrid RFQ is proposed to accelerate a high-intensity low-energy heavy ion beam in HISCL （High Intensive heavy ion SuperConducting Linear accelerator）, which is an injector of HIAF （Heavy Ion Advanced Research Facility）. It is combined by an alternative series of acceleration gaps and RFQ sections. The proposed structure has a high accelerating ability compared with a conventional RFQ and is more compact than traditional DTLs. A Hybrid RFQ is designed to accelerate 238U34＋ from 0.38 MeV/u to 1.33 MeV/u. The operation frequency is described to be 81.25 MHz at CW （continuous wave） mode. The design beam current is 1.0 mA. The results of beam dynamics and RF simulation of the Hybrid RFQ show that the structure has a good performance at the energy range for ion acceleration. The emittance growth is less than 5% in both directions and the RF power is less than 150 kW. In this paper, the results of beam dynamics and RF simulation of the Hybrid RFQ are presented.     

SSC直线注入器RFQ腔体多物理场分析

SSC-LINAC是为兰州重离子研究装置（HIRFL）设计的直线注入器,它将U34+离子加速到1 MeV/u注入到分离扇回旋加速器（SSC）中,为冷却储存环（CSR）提供10 MeV/u的U34+。该注入器可以将SSC引出的重离子流强提高一个量级以上。SSC-LINAC由一个RFQ（Radio Frequency Quadrupole）加速器和4个DTL（drift tube linac）组成,设计频率为53.667 MHz。RFQ工作在连续波模式,设计功率30 kW,如果不能有效地冷却,高频电流在电极表面产生的热量会使RFQ的腔壁和电极发生形变,从而导致腔体频率的漂移以及加速和聚焦电场的改变。因此,为了保证连续波工作的RFQ加速器稳定运行,对水冷模式和通道设计提出了很高的要求。作者用有限元软件ANSYS对RFQ进行高频电磁场、温度场、结构应力的耦合分析,验证了冷却方案设计的可行性和可靠性。Heavy Ion Research Facility at Lanzhou(HIRFL) consists of SFC, SSC, CSRm and CSRe. A new linac injector, which will increase U34+ to 1 MeV/u, is designed for SSC to increase the beam intensity to ten times higher. The new injector, whose frequency is 53.667 MHz, is composed by a RFQ (Radio Frequency Quadrupole) cavity and four DTL(Drift Tube Linac) cavities. The RFQ cavity, whose RF power is 30 kW, is operated at CW(continuous wave) mode. The heat produced by HF (high frequency) electromagnetic will cause deformation of RFQ structure, lead to the resonant frequency shift, and reduce the focusing efficiency of the cavity. An efficient cooling system is necessary to ensure that the RFQ cavity can stably be operated at the nominal frequency. A detailed multi-physics field coupling analysis of RFQ has been finished with 3D finite elements software ANSYS. The result of the analysis shows that the water cooling system can cool the RFQ cavity fully and keep the frequency drift be in a acceptable level.     

Theoretical Design of a 104MHz Ladder Type IH-RFQ Accelerator

Beam dynamics and rf designs of a 104 MHz ladder type IH-RFQ （L-IH-RFQ） accelerator are finished at Peking University for the acceleration of 14C＋ from 40 keV to 500 keV. As a specific feature, the output beam energy spread is as low as 0.6% achieved with the internal discrete bunching method, which makes potential applications of RFQ feasible, such as accelerator mass spectrometry and ion implantation. Tolerances of the beam dynamics design are studied by means of changing the input beam parameters, and the results are quite satisfying. On the other hand, the L-IH-RFQ structure is employed, taking advantage of its mechanical stability and the absence of inter-electrode voltage asymmetry. Radio-frequency properties are studied and optimized for reducing power loss with Microwave Studio （MWS）. Tuning of the field flatness and frequency is investigated in principle.     

Physics design for the C-ADS main linac based on two dif f erent injector design schemes

The China ADS（C-ADS） project proposes to build a 1000 MW Accelerator Driven sub-critical System around 2032. The accelerator will work in CW mode with 10 mA in beam current and 1.5 GeV in final beam energy. The linac is composed of two major sections： the injector section and the main linac section. There are two diferent schemes for the injector section. The Injector-scheme is based on a 325 MHz RFQ and superconducting spoke cavities of the same RF frequency and the Injector-scheme is based on a 162.5 MHz RFQ and superconducting HWR cavities of the same frequency. The main linac design will be diferent for diferent injector choices. The two diferent designs for the main linac have been studied according to the beam characteristics from the diferent injector schemes.     

Latest progress of the RFQ cooler and buncher RFQ1L

The RFQ cooler and buncher RFQ1L is a key device of the SHANS (Spectrometer for Heavy Atoms and Nuclear Structure). The status of the machining and assembly of the central part is introduced, and the structure of the whole RFQ1L system and the preliminary plan for the testing are discussed also.     

200 MHz质子带窗四翼型射频四极场加速器结构模拟研究

根据束流动力学设计方案,使用电磁场计算软件CST Microwave Studio对带窗四翼型射频四极场（RFQ）结构进行了模拟研究,分析了加速腔结构参数对其物理特性的影响,得到了200 MHz质子带窗四翼型RFQ优化结构方案。该结构的比分路阻抗为79.5 km,模式间隔达25.802 MHz。与传统的四翼型RFQ比较结果表明：带窗四翼型RFQ具有较低的工作频率范围、良好的电稳定性以及较高的比分路阻抗。     

Conceptional design of a heavy ion linac injector for HIRFL-CSRm

A room temperature heavy ion linac has been proposed as a new injector of the main Cooler Storage Ring(CSRm) at the Heavy Ion Research Facility in Lanzhou(HIRFL), which is expected to improve the performance of HIRFL. The linac injector can supply heavy ions with a maximum mass to charge ratio of 7 and an injection kinetic energy of 7.272 MeV/u for CSRm; the pulsed beam intensity is 3 emA with the duty factor of 3%. Compared with the present cyclotron injector, the Sector Focusing Cyclotron(SFC), the beam current from linac can be improved by 10–100 times. As the pre-accelerator of the linac, the 108.48 MHz 4-rod Radio Frequency Quadrupole(RFQ) accelerates the ion beam from 4 keV/u to 300 keV/u, which achieves the transmission efficiency of 95.3% with a 3.07 m long vane.The phase advance has been taken into account in the analysis of the error tolerance, and parametric resonances have been carefully avoided by adjusting the structure parameters. Kombinierte Null Grad Struktur Interdigital H-mode Drift Tube Linacs(KONUS IH-DTLs), which follow the RFQ, accelerate ions up to the energy of 7.272 MeV/u for CSRm. The resonance frequency is 108.48 MHz for the first two cavities and 216.96 MHz for the last 5 Drift Tube Linacs(DTLs). The maximum accelerating gradient can reach 4.95 MV/m in a DTL section with the length of17.066 m, and the total pulsed RF power is 2.8 MW. A new strategy, for the determination of resonance frequency,RFQ vane voltage and DTL effective accelerating voltage, is described in detail. The beam dynamics design of the linac will be presented in this paper.     

200MHz质子带窗四翼型射频四极场加速器结构模拟研究

根据束流动力学设计方案,使用电磁场计算软件CST Microwave Studio对带窗四翼型射频四极场(RFQ)结构进行了模拟研究,分析了加速腔结构参数对其物理特性的影响,得到了200MHz质子带窗四翼型RFQ优化结构方案。该结构的比分路阻抗为79.5kΩ·m,模式间隔达25.802MHz。与传统的四翼型RFQ比较结果表明:带窗四翼型RFQ具有较低的工作频率范围、良好的电稳定性以及较高的比分路阻抗。     

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.     

一米长四翼型RFQ调谐研究(英文)

为获取ADS工程中四翼型RFQ加速器在设计、调谐和运行等方面的经验,设计和建造了一台一米长四翼型RFQ加速器。该RFQ的设计频率为162.5 MHz,但是测量结果显示即使没有调谐器时,腔体的频率也为163.7 MHz。为降低腔体频率,使用四线模型理论进行了分析并重新设计了腔体的端板。使用了二极模稳定杆来加大四极频率与相邻二极频率的间隔。最终测量结果显示,在腔体电压分布没有大的波动的情况下腔体频率达到了设计频率。同时,腔体Q值降低了1%,这就要求需要更多的功率注入腔体。使用水对二极模稳定杆进行了冷却,以便腔体能够稳定工作。     

Frequency tuning with RFQ temperature in China ADS Injector Ⅱ

A 162.5 MHz four-vane radio frequency quadruple(RFQ) accelerator has been developed at the Institute of Modern Physics(IMP) for Injector II of the China ADS linac. The RFQ will operate in continuous wave mode at 100 k W. For the designed 10 mA beam, the additional RF power dissipation will induce a very large reflection of power. A water-temperature controlling system will be used to reduce the power reflection by tuning the frequency of the RFQ. The tuning capability of the water temperature is studied under different configurations of cooling water.Simulations and experiment are compared in this paper. The experimental results agree well with simulation using ANSYS. This can be used as a reference to tune the RFQ in beam commissioning.     

Design study of a radio-frequency quadrupole for high-intensity beams

The Rare isotope Accelerator Of Newness(RAON) heavy-ion accelerator has been designed for the Rare Isotope Science Project(RISP) in Korea. The RAON will produce heavy-ion beams from 660-MeV-proton to200-MeV/u-uranium with continuous wave(CW) power of 400 k W to support research in various scientific fields.Its system consists of an ECR ion source, LEBTs with 10 ke V/u, CW RFQ accelerator with 81.25 MHz and 500 ke V/u, a MEBT system, and a SC linac. In detail, the driver linac system consists of a Quarter Wave Resonator(QWR) section with 81.25 MHz and a Half Wave Resonator(HWR) section with 162.5 MHz, Linac-1, and a Spoke Cavity section with 325 MHz, Linac-2. These linacs have been designed to optimize the beam parameters to meet the required design goals. At the same time, a light-heavy ion accelerator with high-intensity beam, such as proton,deuteron, and helium beams, is required for experiments. In this paper, we present the design study of the high intensity RFQ for a deuteron beam with energies from 30 ke V/u to 1.5 MeV/u and currents in the m A range. This system is composed of an Penning Ionization Gauge ion source, short LEBT with a RF deflector, and shared SC Linac. In order to increase acceleration efficiency in a short length with low cost, the 2nd harmonic of 162.5 MHz is applied as the operation frequency in the D~+RFQ design. The D~+RFQ is designed with 4.97 m, 1.52 bravery factor. Since it operates with 2nd harmonic frequency, the beam should be 50% of the duty factor while the cavity should be operated in CW mode, to protect the downstream linac system. We focus on avoiding emittance growth by the space-charge effect and optimizing the RFQ to achieve a high transmission and low emittance growth. Both the RFQ beam dynamics study and RFQ cavity design study for two and three dimensions will be discussed.     

Design of 57.5 MHz CW RFQ structure for the Rare Isotope Accelarator Facility

The Rare Isotope Accelerator (RIA) facility includes a driver LINAC for production of 400 kW CW heavy-ion beams. The initial acceleration of heavy ions delivered from an ECR ion source can be effectively performed by a 57.5 MHz 4 m long RFQ. The principal specifications of the RFQ are: (1) formation of extremely low longitudinal emittance: (2) stable operation over a wide range of voltage for acceleration of various ion species needed for RIA operation; (3) simultaneous acceleration of two-charge states of uranium ions. CW operation of an accelerating structure leads to a number of requirements for the resonators such as high shunt impedance, efficient water cooling of all parts of the resonant cavity, mechanical stability together with precise alignment, reliable rf contacts, a stable operating mode and fine tuning of the resonant frequency during operation. To satisfy these requirements a new resonant structure has been developed. This paper discusses beam dynamics and electrodynamics design of the RFQ cavity, as well as, some aspects of the mechanical design of this low-frequency CW RFQ.     

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.     

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.