Electron cloud interaction with high energy positive beams are believed responsible for various undesirable effects such as vacuum degradation, collective beam instability and even beam loss in high power proton circu...Electron cloud interaction with high energy positive beams are believed responsible for various undesirable effects such as vacuum degradation, collective beam instability and even beam loss in high power proton circular accelerators. An important uncertainty in predicting electron cloud instability lies in the detailed processes of the generation and accumulation of the electron cloud. The simulation on the build-up of electron cloud is necessary to further studies on beam instability caused by electron clouds. The China Spallation Neutron Source （CSNS） is an intense proton accelerator facility now being built, whose accelerator complex includes two main parts： an H-linac and a rapid cycling synchrotron （RCS）. The RCS accumulates the 80 MeV proton beam and accelerates it to 1.6 GeV with a repetition rate of 25 Hz. During beam injection with lower energy, the emerging electron cloud may cause serious instability and beam loss on the vacuum pipe. A simulation code has been developed to simulate the build-up, distribution and density of electron cloud in CSNS/RCS.展开更多
In order to meet the requirements of the Circular Electron Positron Collider(CEPC),a 650-MHz 2-cell superconducting cavity was proposed and designed.In this study,we show the progress in the cavity design for the CEPC...In order to meet the requirements of the Circular Electron Positron Collider(CEPC),a 650-MHz 2-cell superconducting cavity was proposed and designed.In this study,we show the progress in the cavity design for the CEPC.The radio frequency and mechanical designs are ready for the first design version,called CEPC-V1.A cryomodule,which consists of two 650-MHz 2-cell cavities,was scheduled the last year.Therefore,prototypes of the 2-cell cavity based on this design were fabricated and tested the following year.The vertical test results show that multipacting(MP)exists from 10 to 19 MV/m.This will increase the operational risk of the CEPC,while the continuous-wave operation for the 650-MHz cavity is 19.7 MV/m.Two trapped modes were also found,which exist because of the identical half-cell design.Therefore,a few improvements regarding MP and more efficient extraction of higher-order mode power are discussed.A new type of cavity design,called CEPC-V2,is also discussed in this paper.展开更多
An RF power coupler is one of the key components in a superconducting （SC） linac. It provides RF power to the SC cavity and interconnects different temperature layers （1.8 K, 4.2 K, 70 K and 300 K）. The TTF-Ⅲ cou...An RF power coupler is one of the key components in a superconducting （SC） linac. It provides RF power to the SC cavity and interconnects different temperature layers （1.8 K, 4.2 K, 70 K and 300 K）. The TTF-Ⅲ coupler is one of the most promising candidates for the High Energy （HE） linac of Project X, but it cannot meet the average power requirements because of the relatively high temperature rise on the warm inner conductor, so some design modifications will be required. In this paper, we describe our simulation studies on the copper coating thickness on the warm inner conductor with RRR values of 10 and 100. Our purpose is to rebalance the dynamic and static loads, and finally lower the temperature rise along tbe warm inner conductor. In addition, to get stronger coupling, better power handling and less multipacting probability, one new cold part design was proposed using a 60 mm coaxial line; the corresponding multipacting simulation studies have also been investigated.展开更多
Modeling multipacting to steady state saturation is of interest in determining the performance of the micro-pulse electron gun. In this paper, a novel method is proposed to calculate the multipacting resonance param- ...Modeling multipacting to steady state saturation is of interest in determining the performance of the micro-pulse electron gun. In this paper, a novel method is proposed to calculate the multipacting resonance param- eters for the gun. This method works well, and the 2-D simulation results suggest that steady state saturation can be achieved in the gun. After saturation the transition from two-surface multipacting to single-surface multipacting occurred, and an extensive range of electron emission time is a suggested way to avoid this kind of transition.展开更多
Since the tapered quarter wave resonator （QWR） cavity is proven to have a much lower peak surface magnetic field in the short plate and a lower peak surface electric field near the beam tube compared with the straig...Since the tapered quarter wave resonator （QWR） cavity is proven to have a much lower peak surface magnetic field in the short plate and a lower peak surface electric field near the beam tube compared with the straight outer conductor QWR, it has been recommended for the separated sector cyclotron linac injector system in the heavy ion research facility in Lanzhou. This paper is focused on the multipacting （MP） analysis for the tapered QWR with a frequency of 80.5 MHz and beta of 0.085. Using the Analyst program, MP bands can be simulated and analyzed with the Particle Tracking module to identify potential problems in the cavity design. This paper will present the simulation results of MP for the tapered QWR cavity.展开更多
A novel parallel plate model is proposed that divides the electron cloud into three parts at saturation, and it is studied in detail using both an analytical approach and particle-in-cell （PIC） code simulations. As ...A novel parallel plate model is proposed that divides the electron cloud into three parts at saturation, and it is studied in detail using both an analytical approach and particle-in-cell （PIC） code simulations. As one part of the electron cloud, ribbons modes are suggested by tracking the trajectory of individual particles, and the aim of this mode form is to simplify the progress of the multipacting effect in the parallel plate so as to be eliminated by optimizing RF parameters. The micro-pulse electron gun （MPG） has demonstrated the potential to address the need for high peak and average current electron beams, hence studying the multipacting in MPG is essential. On the basis of studying multipacting in the parallel plate, it is clear that increasing the cavity voltage is of interest in yielding high quality beams in the gun.展开更多
During the design process, multipacting effect has been taken into consideration using a 2D simulation code MultiPac and all of the corners are rounded to suppress the multipacting effect in the pill-box cavity. Howev...During the design process, multipacting effect has been taken into consideration using a 2D simulation code MultiPac and all of the corners are rounded to suppress the multipacting effect in the pill-box cavity. However, unexpected multipacting effect prevents the increase of the input power when the magnetic field of focusing coils is added after adequate conditioning and a novel method is adopted to suppress it by introducing extra coils to counteract the field. This paper focuses on the simulation of multipacting effect in different magnetic field configurations. The experimental observations and simulation results of multipacting effect are presented and details of the multipacting process are also analyzed.展开更多
A number of superconducting cavities of axis-symmetric geometry have been considered to study the effect in order to achieve the desired performance. It is shown that the multipacting effect is strongly dependent on t...A number of superconducting cavities of axis-symmetric geometry have been considered to study the effect in order to achieve the desired performance. It is shown that the multipacting effect is strongly dependent on the condition of the RF surface and can be suppressed with reconsideration of the geometry. The simulation result is compared with the result of the semi-analytical model in the end.展开更多
This paper presents the first phase of design, analysis, and simulation for the klystron coaxial radio frequency（RF）output window. This study is motivated by 800 kW continuous wave（CW）, 650 MHz klystrons for the f...This paper presents the first phase of design, analysis, and simulation for the klystron coaxial radio frequency（RF）output window. This study is motivated by 800 kW continuous wave（CW）, 650 MHz klystrons for the future plan of circular electron–positron collider（CEPC） project. The RF window which is used in the klystron output section has a function to separate the klystron from the inner vacuum side to the outside, and high RF power propagates through the window with small power dissipation. Therefore, the window is a key component for the high power klystron. However, it is vulnerable to the high thermal stress and multipacting, so this paper presents the window design and analysis for these problems. The microwave design has been performed by using the computer simulation technology（CST） microwave studio and the return loss of the window has been established to be less than-90 d B. The multipacting simulation of the window has been carried out using MultiPac and CST particles studio. Through the multipacting analysis, it is shown that with thin coating of TiN, the multipacting effect has been suppressed effectively on the ceramic surface. The thermal analysis is carried out using ANSYS code and the temperature of alumina ceramic is lower than 310 K with water cooling.The design result successfully meets the requirement of the CEPC 650 MHz klystron. The manufacturing and high power test plan are also described in this paper.展开更多
The simulation and analysis for electron multipacting phenomenon in a low β spoke superconducting cavity in ADS proton accelerator are proposed. Using both CST and Track3P codes, the electron multipacting calculation...The simulation and analysis for electron multipacting phenomenon in a low β spoke superconducting cavity in ADS proton accelerator are proposed. Using both CST and Track3P codes, the electron multipacting calculation for β=0.12 spoke superconducting cavity is implemented. The methods of multipacting calculation on both codes are studied and described. With the comparison between the calculation results and the cavity vertical test result, the accuracy and reliability of different codes on calculating multipacting are analyzed. Multipacting calculation can help to understand the results of vertical test and also can help to do the optimization in cavity design.展开更多
In the China ADS（CIADS） proton accelerator, multipacting is an issue of concern for the superconducting cavities. The parallel codes Omega3 P and Track3 P, developed at SLAC under the support of the DOE Sci DAC prog...In the China ADS（CIADS） proton accelerator, multipacting is an issue of concern for the superconducting cavities. The parallel codes Omega3 P and Track3 P, developed at SLAC under the support of the DOE Sci DAC program, have been used to calculate the electromagnetic field distribution and to analyze the multipacting barriers of such cavities. In this paper, two types of 162.5 MHz half wave resonator cavities, HWR-010（cylinder type with β of 0.10） and HWR-015（taper type with β of 0.15） have been analyzed, and the results of the multipacting analyses show that the resonant electrons occur at different regions with different accelerating gradients. The two-point 1st order multipacting on the short plate has also been researched and discussed.展开更多
Peking University is designing a new SRF gun that is composed of a quarter wave resonator （QWR） and an elliptical cavity. Compared to the elliptical cavity, the QWR is sufficiently compact at the same frequency and...Peking University is designing a new SRF gun that is composed of a quarter wave resonator （QWR） and an elliptical cavity. Compared to the elliptical cavity, the QWR is sufficiently compact at the same frequency and its electric field is quasi-DC. The RF parameters are determined by optimization of QWR cavity structure and the possible multipacting locations are analyzed by 2D MP simulation. The simulation results show that multipacting is not a critical issue for our optimized cavity structure.展开更多
Compact accelerator-based neutron source facilities are garnering attention and play an important and expanding role in material and engineering sciences,as well as in neutron science education and training.Neutrons a...Compact accelerator-based neutron source facilities are garnering attention and play an important and expanding role in material and engineering sciences,as well as in neutron science education and training.Neutrons are produced by bombarding a low-energy proton beam onto a beryllium or lithium target.In such an acceleratorbased neutron source,a radio frequency quadrupole(RFQ)is usually utilized to accelerate a high-intensity proton beam to a few MeV.This study mainly covers the highfrequency structure design optimizations of a 4-vane RFQ with pi-mode stabilizer loops(PISLs)and its RF stability analysis.A 176 MHz RFQ accelerator is designed to operate at a 10%duty factor and could accelerate an80 mA proton beam from 65 keV to 2.5 MeV within a length of 5.3 m.The adoption of PISLs ensures high RF stability,eases the operation of the accelerator,and implies less stringent alignment and machining tolerances.展开更多
Purpose In order to increase CSNS beam power from 100 to 500 kW,the linac injection energy needs to be increased from 80 to 300 MeV.The combined layout of superconducting spoke cavities and elliptical cavities will be...Purpose In order to increase CSNS beam power from 100 to 500 kW,the linac injection energy needs to be increased from 80 to 300 MeV.The combined layout of superconducting spoke cavities and elliptical cavities will be adopted to accelerate H−beam to 300 MeV.In this paper,a compact single spoke cavity withΦ50-mm beam aperture was proposed,with the RF performance of the spoke cavity optimized to Ep/Eacc<5,Bp/Eacc<9,as well as the good multipacting behavior.Methods CST Microwave Studio was used to optimize the RF performance(Epeak/Eacc,Bpeak/Eacc,R/Q)with cavity geometry parameters.After electromagnetic design was finished,multipacting behavior was studied with CST Particle Studio module,and cavity shape modification was made to get a reasonable<SEY>value.Results The simulation got optimum results of Epeak/Eacc=4.97 and Bpeak/Eacc=8.42 mT/(MV/m),and the<SEY>max is 1.52 at Eacc=7.74 MV/m.Conclusion A 648 MHzβg=0.4 single spoke cavity with beam apertureΦ50 mm was proposed in the paper.This compact cavity may be a very promising option for CSNS linac upgrading.In addition to the optimization of the RF parameters,the multipacting behavior of the cavity is also studied,and cavity shape is optimized to reduce<SEY>value.展开更多
基金Supported by National Natural Science Foundation of China(11275221,11175193)
文摘Electron cloud interaction with high energy positive beams are believed responsible for various undesirable effects such as vacuum degradation, collective beam instability and even beam loss in high power proton circular accelerators. An important uncertainty in predicting electron cloud instability lies in the detailed processes of the generation and accumulation of the electron cloud. The simulation on the build-up of electron cloud is necessary to further studies on beam instability caused by electron clouds. The China Spallation Neutron Source （CSNS） is an intense proton accelerator facility now being built, whose accelerator complex includes two main parts： an H-linac and a rapid cycling synchrotron （RCS）. The RCS accumulates the 80 MeV proton beam and accelerates it to 1.6 GeV with a repetition rate of 25 Hz. During beam injection with lower energy, the emerging electron cloud may cause serious instability and beam loss on the vacuum pipe. A simulation code has been developed to simulate the build-up, distribution and density of electron cloud in CSNS/RCS.
基金supported by the National Key Programme for S&T Research and Development(No.2016YFA0400400)
文摘In order to meet the requirements of the Circular Electron Positron Collider(CEPC),a 650-MHz 2-cell superconducting cavity was proposed and designed.In this study,we show the progress in the cavity design for the CEPC.The radio frequency and mechanical designs are ready for the first design version,called CEPC-V1.A cryomodule,which consists of two 650-MHz 2-cell cavities,was scheduled the last year.Therefore,prototypes of the 2-cell cavity based on this design were fabricated and tested the following year.The vertical test results show that multipacting(MP)exists from 10 to 19 MV/m.This will increase the operational risk of the CEPC,while the continuous-wave operation for the 650-MHz cavity is 19.7 MV/m.Two trapped modes were also found,which exist because of the identical half-cell design.Therefore,a few improvements regarding MP and more efficient extraction of higher-order mode power are discussed.A new type of cavity design,called CEPC-V2,is also discussed in this paper.
文摘An RF power coupler is one of the key components in a superconducting （SC） linac. It provides RF power to the SC cavity and interconnects different temperature layers （1.8 K, 4.2 K, 70 K and 300 K）. The TTF-Ⅲ coupler is one of the most promising candidates for the High Energy （HE） linac of Project X, but it cannot meet the average power requirements because of the relatively high temperature rise on the warm inner conductor, so some design modifications will be required. In this paper, we describe our simulation studies on the copper coating thickness on the warm inner conductor with RRR values of 10 and 100. Our purpose is to rebalance the dynamic and static loads, and finally lower the temperature rise along tbe warm inner conductor. In addition, to get stronger coupling, better power handling and less multipacting probability, one new cold part design was proposed using a 60 mm coaxial line; the corresponding multipacting simulation studies have also been investigated.
基金Supported by National Basic Research Program of China(973 Program)(2011CB808300)National Natural Science Foundation of China(10935011)
文摘Modeling multipacting to steady state saturation is of interest in determining the performance of the micro-pulse electron gun. In this paper, a novel method is proposed to calculate the multipacting resonance param- eters for the gun. This method works well, and the 2-D simulation results suggest that steady state saturation can be achieved in the gun. After saturation the transition from two-surface multipacting to single-surface multipacting occurred, and an extensive range of electron emission time is a suggested way to avoid this kind of transition.
基金Supported by National Nature Science Foundation of China(91026001)
文摘Since the tapered quarter wave resonator （QWR） cavity is proven to have a much lower peak surface magnetic field in the short plate and a lower peak surface electric field near the beam tube compared with the straight outer conductor QWR, it has been recommended for the separated sector cyclotron linac injector system in the heavy ion research facility in Lanzhou. This paper is focused on the multipacting （MP） analysis for the tapered QWR with a frequency of 80.5 MHz and beta of 0.085. Using the Analyst program, MP bands can be simulated and analyzed with the Particle Tracking module to identify potential problems in the cavity design. This paper will present the simulation results of MP for the tapered QWR cavity.
基金Supported by National Basic Research Program of China(973 Program)(2011CB808300)National Natural Science Foundation of China(10935011)
文摘A novel parallel plate model is proposed that divides the electron cloud into three parts at saturation, and it is studied in detail using both an analytical approach and particle-in-cell （PIC） code simulations. As one part of the electron cloud, ribbons modes are suggested by tracking the trajectory of individual particles, and the aim of this mode form is to simplify the progress of the multipacting effect in the parallel plate so as to be eliminated by optimizing RF parameters. The micro-pulse electron gun （MPG） has demonstrated the potential to address the need for high peak and average current electron beams, hence studying the multipacting in MPG is essential. On the basis of studying multipacting in the parallel plate, it is clear that increasing the cavity voltage is of interest in yielding high quality beams in the gun.
文摘During the design process, multipacting effect has been taken into consideration using a 2D simulation code MultiPac and all of the corners are rounded to suppress the multipacting effect in the pill-box cavity. However, unexpected multipacting effect prevents the increase of the input power when the magnetic field of focusing coils is added after adequate conditioning and a novel method is adopted to suppress it by introducing extra coils to counteract the field. This paper focuses on the simulation of multipacting effect in different magnetic field configurations. The experimental observations and simulation results of multipacting effect are presented and details of the multipacting process are also analyzed.
文摘A number of superconducting cavities of axis-symmetric geometry have been considered to study the effect in order to achieve the desired performance. It is shown that the multipacting effect is strongly dependent on the condition of the RF surface and can be suppressed with reconsideration of the geometry. The simulation result is compared with the result of the semi-analytical model in the end.
基金Project supported by Yifang Wang’s Science Studio of the Ten Thousand Talents Project,China
文摘This paper presents the first phase of design, analysis, and simulation for the klystron coaxial radio frequency（RF）output window. This study is motivated by 800 kW continuous wave（CW）, 650 MHz klystrons for the future plan of circular electron–positron collider（CEPC） project. The RF window which is used in the klystron output section has a function to separate the klystron from the inner vacuum side to the outside, and high RF power propagates through the window with small power dissipation. Therefore, the window is a key component for the high power klystron. However, it is vulnerable to the high thermal stress and multipacting, so this paper presents the window design and analysis for these problems. The microwave design has been performed by using the computer simulation technology（CST） microwave studio and the return loss of the window has been established to be less than-90 d B. The multipacting simulation of the window has been carried out using MultiPac and CST particles studio. Through the multipacting analysis, it is shown that with thin coating of TiN, the multipacting effect has been suppressed effectively on the ceramic surface. The thermal analysis is carried out using ANSYS code and the temperature of alumina ceramic is lower than 310 K with water cooling.The design result successfully meets the requirement of the CEPC 650 MHz klystron. The manufacturing and high power test plan are also described in this paper.
文摘The simulation and analysis for electron multipacting phenomenon in a low β spoke superconducting cavity in ADS proton accelerator are proposed. Using both CST and Track3P codes, the electron multipacting calculation for β=0.12 spoke superconducting cavity is implemented. The methods of multipacting calculation on both codes are studied and described. With the comparison between the calculation results and the cavity vertical test result, the accuracy and reliability of different codes on calculating multipacting are analyzed. Multipacting calculation can help to understand the results of vertical test and also can help to do the optimization in cavity design.
基金Supported by National Natural Science Foundation(11221064,91026001)
文摘In the China ADS（CIADS） proton accelerator, multipacting is an issue of concern for the superconducting cavities. The parallel codes Omega3 P and Track3 P, developed at SLAC under the support of the DOE Sci DAC program, have been used to calculate the electromagnetic field distribution and to analyze the multipacting barriers of such cavities. In this paper, two types of 162.5 MHz half wave resonator cavities, HWR-010（cylinder type with β of 0.10） and HWR-015（taper type with β of 0.15） have been analyzed, and the results of the multipacting analyses show that the resonant electrons occur at different regions with different accelerating gradients. The two-point 1st order multipacting on the short plate has also been researched and discussed.
基金Supported by National Basic Research Project(2011CB808302)National Natural Science Funds(11075007)
文摘Peking University is designing a new SRF gun that is composed of a quarter wave resonator （QWR） and an elliptical cavity. Compared to the elliptical cavity, the QWR is sufficiently compact at the same frequency and its electric field is quasi-DC. The RF parameters are determined by optimization of QWR cavity structure and the possible multipacting locations are analyzed by 2D MP simulation. The simulation results show that multipacting is not a critical issue for our optimized cavity structure.
文摘Compact accelerator-based neutron source facilities are garnering attention and play an important and expanding role in material and engineering sciences,as well as in neutron science education and training.Neutrons are produced by bombarding a low-energy proton beam onto a beryllium or lithium target.In such an acceleratorbased neutron source,a radio frequency quadrupole(RFQ)is usually utilized to accelerate a high-intensity proton beam to a few MeV.This study mainly covers the highfrequency structure design optimizations of a 4-vane RFQ with pi-mode stabilizer loops(PISLs)and its RF stability analysis.A 176 MHz RFQ accelerator is designed to operate at a 10%duty factor and could accelerate an80 mA proton beam from 65 keV to 2.5 MeV within a length of 5.3 m.The adoption of PISLs ensures high RF stability,eases the operation of the accelerator,and implies less stringent alignment and machining tolerances.
基金the China Spallation Neutron Source project—the National Science Foundation of China(Grant No.11575289)State Key Laboratory of Particle Detection and Electronics(Institute of High Energy Physics,CAS and University of Science and Technology of China)and Key Laboratory of Particle Acceleration Physics andTechnology(Institute of High Energy Physics,CAS).
文摘Purpose In order to increase CSNS beam power from 100 to 500 kW,the linac injection energy needs to be increased from 80 to 300 MeV.The combined layout of superconducting spoke cavities and elliptical cavities will be adopted to accelerate H−beam to 300 MeV.In this paper,a compact single spoke cavity withΦ50-mm beam aperture was proposed,with the RF performance of the spoke cavity optimized to Ep/Eacc<5,Bp/Eacc<9,as well as the good multipacting behavior.Methods CST Microwave Studio was used to optimize the RF performance(Epeak/Eacc,Bpeak/Eacc,R/Q)with cavity geometry parameters.After electromagnetic design was finished,multipacting behavior was studied with CST Particle Studio module,and cavity shape modification was made to get a reasonable<SEY>value.Results The simulation got optimum results of Epeak/Eacc=4.97 and Bpeak/Eacc=8.42 mT/(MV/m),and the<SEY>max is 1.52 at Eacc=7.74 MV/m.Conclusion A 648 MHzβg=0.4 single spoke cavity with beam apertureΦ50 mm was proposed in the paper.This compact cavity may be a very promising option for CSNS linac upgrading.In addition to the optimization of the RF parameters,the multipacting behavior of the cavity is also studied,and cavity shape is optimized to reduce<SEY>value.
